Vegetal Waste

32
Review paper Transformation of vegetable waste into value added products: (A) the upgrading concept; (B) practical implementations Gunther Laufenberg a, * , Benno Kunz a , Marianne Nystroem b a Department of Food Technology, University Bonn, Roemerstr. 164, D-53117 Bonn, Germany b Department of Chemical Technology, Lappeenranta University of Technology, Postbox 20, FIN-53851 Lappeenranta, Finland Abstract Waste can contain many reusable substances of high value. Depending on there being an adequate technology this residual matter can be converted into commercial products either as raw material for secondary processes, as operating supplies or as in- gredients of new products. Numerous valuable substances in food production are suitable for separation and recycling at the end of their life cycle, even though present separation and recycling processes are not absolutely cost efficient. In Part A a need statement is visualised––based on a holistic concept of food production––for the vegetable industry, recording occurrence, quantities and utilisation of the residual products. A literature survey, covering more than 160 articles from all over the world, plus our own investigations summarises the latest knowledge in the above-mentioned field and outline prospects for future economic treatment of vegetable ‘co-products’. The main goal of a clean production process is demonstrated by three practical implementations in Part B: 1. Upgrading of vegetable residues for the production of novel types of products: multifunctional food ingredients in fruit juice and bakery goods. 2. Bioconversion via solid-state fermentation: vegetable residues as an exclusive substrate for the generation of fruity food flavours. 3. Conversion of vegetable residues into operating supplies: bioadsorbents for waste water treatment. The investigations are promising with regard to future application in the mentioned industrial branch. The outlined concept can be naturally transferred to several areas of industrial food production. The intentions of this research area are located at the de- velopment of techniques, which fulfil the conditions of environmental protection with costs to a minimum. The prospect of several new niche markets is worthwhile indeed. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Green productivity; Vegetable waste treatment; Clean production; Valuable substances; Bioadsorbents; Upgrading; Recycling; Bioflavours; Multifunctional food ingredient; Review Part A 1. Introduction A thing is right when it tends to preserve the inte- grity, stability and beauty of the biotic community. It is wrong when it tends to do otherwise. (Aldo Leopold) Today’s society, in which there is a great demand for appropriate nutritional standards, is characterized by rising costs and often decreasing availability of raw materials together with much concern about environ- mental pollution. Consequently there is a considerable emphasis on the recovery, recycling and upgrading of wastes. This is particularly valid for the food and food processing industry in which wastes, effluents, residues, and by-products can be recovered and can often be upgraded to higher value and useful products. The food industry produces large volumes of wastes, both solids and liquids, resulting from the production, preparation, and consumption of food. These wastes pose increasing disposal and potentially severe pollution Bioresource Technology 87 (2003) 167–198 * Corresponding author. Tel.: +49-228-734-274; fax: +49-228-734- 429. E-mail address: [email protected] (G. Laufenberg). 0960-8524/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0960-8524(02)00167-0

Transcript of Vegetal Waste

Page 1: Vegetal Waste

Review paper

Transformation of vegetable waste into value added products:

(A) the upgrading concept; (B) practical implementations

G€uunther Laufenberg a,*, Benno Kunz a, Marianne Nystroem b

a Department of Food Technology, University Bonn, Roemerstr. 164, D-53117 Bonn, Germanyb Department of Chemical Technology, Lappeenranta University of Technology, Postbox 20, FIN-53851 Lappeenranta, Finland

Abstract

Waste can contain many reusable substances of high value. Depending on there being an adequate technology this residual

matter can be converted into commercial products either as raw material for secondary processes, as operating supplies or as in-

gredients of new products. Numerous valuable substances in food production are suitable for separation and recycling at the end of

their life cycle, even though present separation and recycling processes are not absolutely cost efficient.

In Part A a need statement is visualised––based on a holistic concept of food production––for the vegetable industry, recording

occurrence, quantities and utilisation of the residual products. A literature survey, covering more than 160 articles from all over the

world, plus our own investigations summarises the latest knowledge in the above-mentioned field and outline prospects for future

economic treatment of vegetable ‘co-products’.

The main goal of a clean production process is demonstrated by three practical implementations in Part B:

1. Upgrading of vegetable residues for the production of novel types of products: multifunctional food ingredients in fruit juice and

bakery goods.

2. Bioconversion via solid-state fermentation: vegetable residues as an exclusive substrate for the generation of fruity food flavours.

3. Conversion of vegetable residues into operating supplies: bioadsorbents for waste water treatment.

The investigations are promising with regard to future application in the mentioned industrial branch. The outlined concept can

be naturally transferred to several areas of industrial food production. The intentions of this research area are located at the de-

velopment of techniques, which fulfil the conditions of environmental protection with costs to a minimum. The prospect of several

new niche markets is worthwhile indeed.

� 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Green productivity; Vegetable waste treatment; Clean production; Valuable substances; Bioadsorbents; Upgrading; Recycling;

Bioflavours; Multifunctional food ingredient; Review

Part A

1. Introduction

A thing is right when it tends to preserve the inte-grity, stability and beauty of the biotic community.

It is wrong when it tends to do otherwise.

(Aldo Leopold)

Today’s society, in which there is a great demand for

appropriate nutritional standards, is characterized by

rising costs and often decreasing availability of rawmaterials together with much concern about environ-

mental pollution. Consequently there is a considerable

emphasis on the recovery, recycling and upgrading of

wastes. This is particularly valid for the food and food

processing industry in which wastes, effluents, residues,

and by-products can be recovered and can often be

upgraded to higher value and useful products.

The food industry produces large volumes of wastes,both solids and liquids, resulting from the production,

preparation, and consumption of food. These wastes

pose increasing disposal and potentially severe pollution

Bioresource Technology 87 (2003) 167–198

*Corresponding author. Tel.: +49-228-734-274; fax: +49-228-734-

429.

E-mail address: [email protected] (G. Laufenberg).

0960-8524/03/$ - see front matter � 2002 Elsevier Science Ltd. All rights reserved.

PII: S0960-8524 (02 )00167-0

Page 2: Vegetal Waste

problems and represent a loss of valuable biomass andnutrients. In the past they often have been dumped or

used without treatment for animal feed or as fertilizers.

In the last few years, however, owing to the increasing

necessity to take into consideration aspects aimed at

preventing pollution of the environment as well as for

economic motives, and the need to conserve energy and

new materials, new methods and policies for waste

handling and treatment have been introduced in therecovery, bioconversion, and utilization of valuable con-

stituents from food processing wastes. Besides their

pollution and hazardous aspects, in many cases, food

processing wastes might have a potential for recycling

raw materials or for conversion into useful products of

higher value as a by-product, or even as raw material for

other industries, or for the use as food or feed/fodder

after biological treatment. Particularly, the bioconver-sion of food processing residues is receiving increased

attention regarding the fact that these residual matters

represent a possible and utilizable resource for conver-

sion to useful products (Martin, 1998, p. 316ff).

1.1. Clean production strategy

Clean production can be considered so far as a strategic

element in manufacturing technology for present and

future products in several industrial branches. Demand is

focused on the development of cost effective technology,

the optimisation of processes including separation steps,alternative processes for the reduction of wastes, optimi-

sation of the use of resources and improvement in pro-

duction efficiency (Paul and Ohlrogge, 1998).

Hence current industrial waste management tech-

niques can be classified into three options: source re-

duction via in-plant modification, waste recovery/recycle

or waste treatment by detoxifying, neutralising or des-

troying the undesirable compounds.The first two options plant modification and waste

recovery/recycle represent the most promising waste

management strategies. Indeed waste recovery is a par-

ticularly attractive option. Significant environmental

and economic benefits can accrue from separating in-

dustrial wastes with the objective of recycling/reusing

these valuable components and/or the bulk of water.

Promising concepts include pervaporation in hybridprocesses (Hausmanns et al., 1999) or the upgrading of

vegetable residues to create a secondary use for the

‘‘waste products’’ (Laufenberg et al., 1999).

It has become apparent that the current practices of

pollution control and waste management cannot com-

pletely meet the increasingly stringent requirements for

the reduction of environmental contamination. There-

fore the manufacturing industry has to include theoptimisation of product-integrated environmental pro-

tection into strategic planning, research and develop-

ment. Beside these strategies green productivity can play

an important role. This paper will report on the occur-rence, quantities and current utilisation routes for solid

vegetable waste, the transformation into value added

products and the practical implementation represented

by three possible applications.

1.2. The ‘‘Holistic concept of food production’’

Present R&D in food technology is unthinkablewithout taking environmental aspects into account. A

responsible management of scarce resources is needed

especially in view of tighter living spaces. Based on these

considerations the holistic concept of food production,

shown in Fig. 1 has been developed. What does it mean?

This approach tries to connect differing goals, such as

highest product quality and safety, highest production

efficiency and the integration of environmental aspectsinto product development and food production. Within

the concept every factor and aspect should be taken into

account in a coherent manner.

The recycling of residues is important to every man-

ufacturing branch and includes high developing poten-

tial. A systematic reduction of product losses and

emissions is profitable under both economical and eco-

logical aspects.Concepts like the differentiation and separate treat-

ment of waste water streams and a task oriented

by-product management support this trend, in this

connection special attention is drawn to the recovery of

valuable substances or product losses and internal pro-

cess water recycling.

A Greenpeace briefing published on the web (Kru-

szewska and Thorpe, 1995) defines clean production in asimilar way.

‘‘The goal of clean production is to fulfil our need

for products in a sustainable way i.e., using re-

newable, non-hazardous materials and energy

Fig. 1. The holistic concept of food production.

168 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 3: Vegetal Waste

efficiently while conserving biodiversity. Clean pro-duction systems are circular and use fewer materials

and less water and energy. Resources flow through

the production–consumption cycle at slower rates.

In the first place, a clean production approach

questions the very need for the product or looks

at how else that need could be satisfied or reduced.

Clean production implements the precautionary

principle––it is a new holistic and integrated ap-proach to environmental issues centred around

the product. This approach recognises that most

of our environmental problems––for example

global warming, toxic pollution, loss of biodiver-

sity––are caused by the way and rate at which we

produce and consume resources. It also acknowl-

edges the need for public participation in political

and economic decision-making.’’

Fig. 2 exhibits suggestions for a sustainable economy,beside the preventative approach waste reduction and

recycling is the other most important goal in future.

1.2.1. Development of clean production processes

The outlined system approach results in an opera-

tional program, which is not defined by technological

areas, but by short, medium and long term goals.

Short term goals

• Waste reduction and recycling of valuable sub-stances, by-products and residues.

• Enlargement and adjustment of existing technology

to the application area in particular (e.g., hybrid pro-

cesses).

Outcome: a reduction of emission and risk.

Medium term goals

• Development and application of new and efficient

production processes.

• Adding value to by-products.

Outcome: higher environmental responsibility for the

companies is accompanied by competitive advantages.

Long term goals

• Step by step implementation of environmentally be-

nign manufacturing.

• Development of ‘innovative’ products.

Outcome: Innovative food products like functional/

designer food will open new market segments and addi-

tionally meet clean/green productivity objectives.

1.2.2. Challenge for the vegetable/beverage industry

Considering the vegetable industry the mentioned

goals could be fulfilled by the usual approaches such

as minimisation, disposal, feeding, fertilisation/compo-sting, closed loop production, or conversion.

At present there are few possibilities for the utilisa-

tion or recycling for most of these wastes, the residues

are thus disposed or fed to animals. Transport costs and

sales problems due to the low quality of the residual

matter have led to alternative utilisation concepts, like

the use as a building material, or conversion concepts

like composting and biogas production. Incineration hasbeen largely investigated but not strongly pursued due

to the low calorific value 1 and high water content. An

electric power station in Nimwegen/NL has recently

started to incinerate 40 t of dried coffee grounds from an

instant coffee production plant. Besides the low ‘‘com-

bustion’’ value, a crucial point for all vegetable residues,

the formation of off-odours, bothering the nearby resi-

dents, appears to be another serious problem (Tages-schau, 1999).

Focused on the feeding concept there are further

problems mentioned in the literature. Not every animal

can take every food/residue. Laufenberg et al. (1996)

described that protein concentrate made of potato fruit

water could only be fed to cattle due to the high po-

tassium content, Clemente et al. (1997) found that olive

cake is not recommended for feeding because of itslow digestibility. Sugarcane bagasse has a high lignin

content of 22%, which forms a protective association

with cellulose, thereby causing low digestibility for ani-

mal foodstuff (Purchase, 1995).

According to a survey of the United States Depart-

ment of Agriculture (USDA) estimating and addressing

America’s Food losses (Scott Kantor et al., 1997), about

50 million US$ annually could be saved alone in solidwaste disposal costs for landfills if 5% of processing,

retail, food service and consumer food losses in 1995

were recovered (total amount of loss was 43:54� 109 kg

that year!).

Fig. 2. Circular structure of a sustainable economy (source: adapted

from Stahel Walter R. The Product-life Institute, Geneva).

1 Energetic utilisation is only recommended if the calorific value is

beyond 11,000 kJ kg�1 waste (Kuper-Theodoritis, 1996), which is even

not the fact for fat-containing residues. It has to be doubted if 18,840

kJ kg�1 olive press cakes (Vlyssides et al., 1999) are profitable. Abu-

Qudais (1996) classified the combustion of olive cake as technically

inefficient and economically unacceptable.

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 169

Page 4: Vegetal Waste

1.2.3. End of pipe solution?

The waste to be treated is already produced, a pre-

cautionary approach is possible to a certain extent, but

beyond that the vegetable industry, and especially bev-

erage industry, will always produce residues. The up-

grading concept tries to add value to the by-products

and residues. This medium term goal results in the cre-

ation of innovative products like

• dietary fibres as matrices for flavours, dyes or anti-

oxidants,

• pectin and gelling agents with defined properties

using synergetic effects,

• designer dietary fibres for application in bread or bev-

erages,

• bioflavours produced by bioconversion of waste

material or smart technology like• effective and low cost bioadsorbents, which can be

easily desorbed or biodegraded after use,

• hybrid processes combining adsorption and mem-

brane processes for an advanced wastewater treat-

ment and internal process water recycle.

Thus the introduced concept is a further step to-

wards environmentally benign manufacturing. Theconcept does not present any immediate patent solu-

tions or recipes, because industrial food production

is an interactive process, which needs to fulfil all

three conditions, quality, efficiency and environmental

protection as aforementioned. The upgrading concept

is a continuing development and research strategy,

keeping in mind this interrelated character of produc-

tion.Instead of just blaming the industry to develop a so

far unknown standby preventative solution for the

waste, the outlined concept tries to combine economical

aspects too. The result is a step by step waste reduction

with simultaneously rising productivity, not obtained by

restrictions but by opportunities, advantages are sum-

marised in Table 1.

Consequently the concept follows a three steps app-roach:

1. Evaluation as state of the art, visualising vegetable

waste in its occurrence, quantities and current utilisa-

tion routes.

2. Introducing the upgrading concept.

3. Technical implementation by three selected examples.

2. Need statement: the vegetable waste situation

2.1. Vegetable waste quantities in several countries

The scale of the problem is illustrated by looking at

the total amounts of waste materials produced by dif-

ferent states. Table 2 is a list of waste quantities men-

tioned in the literature.

2.2. Strategies and utilisation routes: state of the art

Special attention was given to publications, which

focus on ideas beyond fodder/feed and composting/fer-

tilisation.

Not covered in this literature survey are

• liquid vegetable waste streams,• any solid or liquid waste stream related to animal

production, slaughtering, meat and meat product

processing.

Vegetable residues mostly contain considerable

amounts of potentially interesting compounds. Due to

legislation and environmental reasons the industry is

more and more forced to find an alternative use for theresidual matter. The recovery of high value compounds

is an elegant way to reuse waste streams, while being

economically interesting on the other hand. Several fruit

and vegetable residues are listed in Table 3.

In the last decade the interest in the alternative use of

waste streams beyond disposal or fertilisation has in-

creased drastically. Further to rising disposal costs the

economic interest has appeared as well. A new nichemarket for residual matter recently appeared in choco-

late production. After a four years discussion the EC has

dropped the purity law for chocolate. The European

Parliament decided on March 8th 2000, that chocolate

manufacturing industry is allowed to add up to 5% other

fat types besides cocoa fat to their chocolate products

(ZDF.MSNBC, 2000). One of the legalised cocoa butter

substitutes is mango kernel, which contains 12% fat(Nanjundaswamy, 1997).

The utilisation of a waste stream as raw material for

new products needs to be economically attractive as

aforementioned. The selection of high value products

reaches from natural bioflavours over food colours to

biocontrolling agents for food preservation.

A real bulk application for vegetable waste––with

minimised further treatment steps––could be the use as abioadsorbent for the pre-treatment of aromatic waste

waters. Activated carbon being used so far is relatively

expensive. In order to obtain cheaper adsorbents,

Table 1

Advantages for industry and environment

� Closed loop of valuable constituents

� Preservation of resources

� Discovery of niche markets

� Environmental protection combined with

� Reduced waste disposal costs

170 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 5: Vegetal Waste

lignocellulosic materials have been studied. Low cost

and simplicity of the modification methods are also

desirable for applications (Peternele et al., 1999).

Another branch for a further use of vegetable resi-

dues is their availability as a source of potential phyto-chemicals. Olive pomace is used as a nematodes

controlling agent for tomatoes (Rodriguez-Kabana

et al., 1995), citrus waste streams are used in horticulture

(Widmer and Montanari, 1995) and mandarin peel

flavonoids are interesting due to their fungistatic activity

(Chkhikvishvili and Gogiya, 1995) which may be ap-

plied to naturally protect vegetables and fruits from

moulding. The limonoid compounds in citrus peel andseeds have recently been found to have important

pharmacological properties as well as potential in the

use as an insect antifeedant for agricultural crops

(Manthey and Grohmann, 1996).

Despite the studies cited and their potentially prom-

ising results, no systematic investigation on poten-

tial utilisation routes and innovative concepts has

been completed yet. Furthermore mechanisms for im-proved yields of existing recycling strategies are not

known.

The improved utilisation of vegetable waste, outlined

here, should lead to a more efficient use of resources

and less negative environmental impact (Sriroth et al.,

2000).

3. The upgrading concept

Important factor for the upgrading process is the

development of a procedure using technical standard

equipment. Goal of the upgrading is a product with

desired, reproducible properties designed under eco-

nomical and ecological conditions.Most of the vegetable residues consist mainly of

water and cellulose and have a poor microbiological

quality because of numerous spoilage bacteria on the

surface, particularly if stored in the production unit

prior to use; thus they quickly decompose in an un-

controlled way. A pre-treatment step in the form of ino-

culation with lactic acid bacteria may produce a more

stable substrate, which should be dried to further en-hance shelf and storage life. An alternative to the fer-

mentation is the acidification by acids like citric, acetic

or ascorbic acid. For sensorial reasons and because of

Table 2

Waste quantities in different countries (selection)

Country/state Quantity and waste type

Germany, 1997 (Henn, 1998) 380,000 t/a organic waste only from potato, vegetable and fruit processing

1,954,000 t/a spent malt and hops (breweries)

1,800,000 t/a grape pomace (viniculture)

3,000,000 t/a crude fibre residues (sugar production)

100,000 t of wet apple pomace (ffi25,000 t dry apple pomace) remain if 400,000 t

of apples are processed into apple juice (Henn and Kunz, 1996)

Belgium, 1992 (Lucas et al., 1997) 105,000 t/a biowaste (vegetable, garden and fruit waste)

280,000 t/a estimations due to legislation of separate household collection

Thailand, 1993 (Prasertsan and Prasertsan, 1996) palm oil

production

386,930 t/a empty fruit bunches

165,830 t/a palm press fibre

110,550 t/a palm kernel shells

1,000,000 t/a cassava pulp (1994, Sriroth et al., 2000)

Spain, 1997 (Clemente et al., 1997) >250,000 t/a olive pomace

EEC, 1996 (Dronnet et al., 1998a) 14,000,000 t/a sugar beet pulp (dry matter!)

Portugal, 1994 (Carvalheiro et al., 1994) 14,000 t/a tomato pomace

Jordan, 1999 (Haddadin et al., 1999) 36,000 t/a olive pomace

Malaysia, 1996 (Hussein et al., 1996) palm oil production 2,520,000 t/a palm mesocarp fibre

1,440,000 t/a oil palm shells

4,140,000 t/a empty fruit bunches

Australia, 1995 (Tran and Mitchell, 1995) 400,000 t/a pineapple peel

USA 300,000 t/a grape pomace in California only (1994) (Nakata, 1994)

9,525 t/a cranberry pomace (1998) (Zheng and Shetty, 1998)

200,000 t/a almond shells (1997) (Toles et al., 2000)

3,300,000 t/a orange peel in Florida (1994) (Manthey and Grohmann, 1996)

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 171

Page 6: Vegetal Waste

Table 3

Current utilisation concepts for vegetable pomace (selection)

Residual matter/co-product Pre-treatment Results Application/secondary use Reference

Almond shells M: grinding, C: phosphoric acid

pre-treatment, P: heat activation

Superior to commercial carbons in metal

uptake, 85–92% with organic solutions

Op: wastewater treatment, metal and or-

ganics adsorption

Toles et al. (2000)

Apple pomace B: SSF Candida, Sacch., Torula

spp., P: drying

Crude protein three times higher, fat 1.5–2

times higher, vitamin C two times higher,

minerals and fibres content higher

O: ethanol, Ff Joshi and Sandhu (1996)

Apple pomace P: drying, M: powdering Enhanced fibre content in food, Sensorial

tests: moderately liked

Fi: pie filling, oatmeal crackers Carson et al. (1994)

Apple pomace B: degradation of linoleic acid by

intrinsic enzyme system of po-

mace

Better results by adding SO2 and Vitamin C O: flavours, volatile aldehydes for chemical

industry

Almosnino and Belin (1991)

Apple pomace – O: Fine chemicals, polyphenols Lu and Foo (1997)

Apple pomace, Pepper

peels

C: CO2 flavour extraction, frac-

tionated precipitation

Fi: flavour extract Bundschuh et al. (1988), Bund-

schuh et al. (1986)

Apple pomace, cassava

bagasse

M: grinding, B: SSF with 4

Rhizopus strains

Highest flavour production with amaranth

plus mineral precursor and apple/cassava/

soybean

Fi: food flavours Christen et al. (2000)

Apple pomace, spent malt

grain

M, B: SSF with Thamnidium

elegans

Highest product yields with ratio of 3 to 1

(AP to SMG), precursor peanut oil further

improved yield

Fi: food supplement c-linolenic acid,

O: pharmaceutical application

Stredansky et al. (2000)

Apricot seeds B: enzymatic degradation Protein substitute only after degradation of

cyanogenic glycosides

Fi: substitute for marzipan, oil for bitter

almond oil, protein enhancer

Tuncel et al. (1998)

Banana pith waste (banana

stem marrow)

M, P: drying, grinding Parameters: agitation time, adsorbent dos-

age, pH-value, initial conc.

O: dye removal in wastewater treatment Namasivayam and Kanchana

(1992)

Blackcurrant and apple

pomace

C, M, P Fibres (60%) are useful for binding Cd

(>30%) and Pb (>40%). Blackcurrant po-

mace binding capacity was higher than for

apple. Ca binding was low, good for food

application

Fi: dietary fibre in food, nutritional value

and healthy food, binding metals, O: binding

capacities for toxic metals potential for

adsorption?

Borycka and Zuchowski (1998)

Carrot pomace M: grinding, B: SSF lactic acid

hygenisation with L. farciminis

In bread: improved nutritional value, fresh-

ness, water binding capacity, sourdough

functions, positive on porosity

Dietary fibre enhancement in bread, sour-

dough substitute in rye and white bread

Filipini and Hogg (1997)

Carrot pomace Fi: cake, dressings, pickles, Fi: bread Ohsawa et al. (1995), Ohsawa

et al. (1994)

Carrot pomace M, P Development of the upgrading process, good

results for stabilisation of several properties

Fi: multifunctional ingredient in beverages Henn and Kunz (1996), Henn

(1998)

Carrot pomace, citrus

and pineapple peels and

pomace

B: SSF A. niger mass multipli-

cation

Biocontrolling agent against Fusarium oxy-

sporum on muskmelon, especially citrus

pomace (20%)

O: biocontrol agent in cultivation of melons Mukherjee and Sen (1998)

Carrot residue, orange

waste, mango peel and

stone

– Egg size and production enhanced with

carrot and orange, neutral with mango stone

Ff: Layer’s hen diet Zia-ur-Rehman et al. (1994)

Cauliflower leaves, cabbage

leaves

B: 1. cellulolytic degradation by

A. niger, 2. Torulopsis utilis, P: 3.

drying

Protein content rose from 14.5% to 22.6% Ff: cattle and poultry Majid et al. (1995)

Citrus by products and

wastes

M, P Influencing the texture and viscosity of the

beverage

Fi: clouding agent in beverages Sreenath et al. (1995)

172

G.Laufen

berg

etal./Bioreso

urce

Tech

nology87(2003)167–198

Page 7: Vegetal Waste

Citrus peel – Pectin extraction, phytochemicals Fi: stabiliser, thickening agent, gelling agent,

soluble fibre, O: several applications

Widmer and Montanari (1995)

Citrus residues, apple po-

mace, sugar beet pulp

B: enzymatic, cellulolytic and

pectinolytic hydrolysis, micro-

bial conversion

O: Pectin, liquid biofuel, substrate for bio-

conversions

Grohmann and Bothast (1994)

Cocoa pod husk, bean

shells and germ

M, P Pectin and protein extraction, germ oil with

high oleic and linoleic acid content

Fi: stabiliser, thickening agent, gelling agent,

soluble fibre, Ff: protein rich pod husk

Nambudiri and Shivashankar

(1985)

Corncob shreds, wheat

straw, wood chips

M: chopping, B: SSF with

Phaenerochaete chrysosporium

and C. versicolor

Corncob shreds and wheat straw showed 70–

75% adsorption rate for textile dyes. In SSF

both substrates have been degraded and dyes

metabolised. Wood chips did not work for

adsorption nor SSF

Op: bioadsorbents for wastewater treatment,

O: soil conditioner after SSF

Nigam et al. (2000)

Corncobs M, P: drying, pyrolysis, C: ZnCl2as activator

O: general use in wastewater treatment Tsai et al. (1998)

Corncobs and onion skin M, P Cu ion adsorption is lignin and cellulose

dependent, simple modifications necessary,

packed bed investigations

Op: alternative bioadsorbents for wastewater

treatment

Odozi and Emelike (1985),

Hawthorne Costa et al. (1995)

Cranberry processing waste B O: SSF, fungal inoculate production Zheng and Shetty (1998)

Fruit pomace – Investigated new dietary fibre compositions

for the application in food

Fi: health quality improvement by adding

fibre product

Borycka (1996)

Galgal peel (citrus pseudo-

limon)

M: powdering, C: pectin extrac-

tion

Fi: as stabilisers, thickening agent, jellies, etc. Attri and Maini (1996)

Grape pomace M: grinding, P: drying Fi: dietary fibre supplement, insoluble is

major fraction

Valiente et al. (1995)

Grape pomace – Nutritional value improved, physiological

properties influenced

Fi Martin-Carron et al. (1997)

Grape pomace Combination of the antioxiden-

tial potential of polyphenols in

grape pomace with the dietary

fibre matrix

Future idea to use the carrier function of

dietary fibres as a matrix for other techno-

logically useful substances (antioxidants,

flavours, dyes, emulsifiers) plus improvement

in nutritional value (fibre, vitamins)

Both fibre enhancement and antioxidants in

food, carrier idea

Saura-Calixto (1998)

Grape pomace, Carrot po-

mace

M: grinding, P: drying, B: SSF,

UASB reactor

O: substrate in bioreactor UASB, Fi: bread

improver, sourdough substitute, dietary fibre

and b-Carotene enhancer

Lucas et al. (1997)

Hawthorn pulp (Mexican

fruit)

– Pectin extraction Fi: stabiliser, thickening agent, gelling agent,

soluble fibre

Higareda et al. (1995)

Jack fruit, pineapple (skin,

stem, leaf) and mango

waste (skin, kernel)

C, M, P Determination of nutritional value, several

analyses

Fi: possible application as food ingredients Haque et al. (1997)

Lemon peel and pulp, olive,

apple and grape pomace

C, P Interactions of dietary fibres with Fe and Ca O: possible adsorbents, Fi: importance for

human nutrition

Torre et al. (1995)

Mandarin fruit waste C: flavonoid extraction High fungistatic activity towards Phoma

tracheiphila, causing citrus malsecco

O: natural fungicide in citrus fruit cultivation Chkhikvishvili and Gogiya

(1995)

Mango kernel C, M Flour substitute with moderate sensory ac-

ceptability, higher calories and protein

Fi: for biscuits Arogba (1999)

Mango peel – Pectin extraction Fi: stabiliser, thickening agent, gelling agent,

soluble fibre

Srirangarajan and Shrikhade

(1976)

G.Laufen

berg

etal./Bioreso

urce

Tech

nology87(2003)167–198

173

Page 8: Vegetal Waste

Table 3 (continued)

Residual matter/co-product Pre-treatment Results Application/secondary use Reference

Mango peel and stone – 15% pectin in the peel, 20-fold flavour

concentrate can be recovered from peel,

stone kernel is rich source of carbohydrates,

protein and fat (12%).

Fi and O: pectin, Kernel fat: use in soap

manufacturing or as cocoa butter substitute,

potential for the preparation of sweetmakers

Nanjundaswamy (1997)

Oat, corn rice, soybean

hulls; pea pods, wheat and

corn bran

M: peeling, purifying, milling,

P: drying

Fi: Z-trim, a fat replacer and texturizing

agent, lowering the calorie content of food

and fibre enhancer

Inglett (1998)

Oil palm shells M, P: drying, pyrolysis, C:

ZnCl2, CO2, as activators

ZnCl2 0–15% impregnation produces decent

microporous carbons

O: activated carbon for adsorption in

chemical industry

Hussein et al. (1996)

Olive cake P: drying, C: extraction with

hexane

Fat oxidation during drying process, hexane

extraction was on no influence on oxidation

Gomes and Caponio (1997)

Olive cake, sugarcane bag-

asse

B: SSF Lipase can degrade the fat in olive cake O: lipase use in chemical, food and phar-

maceutical industry

Cordova et al. (1998)

Olive oil industry waste – Liquid and solid fractions Vitolo et al. (1998)

Olive pomace In mixtures with several chemi-

cals

Phytotoxic if used as an exclusive substance,

in combination with chemicals potential

nematodes controller

O: nematodes controlling agent for tomato

cultivation, potential phytochemical

Rodriguez-Kabana et al. (1995)

Olive pomace Main component is fibre > 70%.

C: extraction, P: drying, chemi-

cal analysis

Analysis used for possible sec. use: nitrogen

value low, amino acid composition well

balanced (except lysine), soluble sugars and

organic acids

Clemente et al. (1997)

Olive pomace P: drying, M: grinding, B: delig-

nification, saccharification

Degradation of lignin, crude protein en-

hancement from 5.9% to 40.3%

Ff: fodder enhancement Haddadin et al. (1999)

Onion skin M, C Stirred tank and packed bed investigations,

parameters are agitation, pH-value, initial

conc., high adsorption rates with a selectivity

towards the heavy metals

Op: alternative bioadsorbents for wastewater

treatment

Kumar and Dara (1981), Bankar

and Dara (1982)

Onions, cull M, C: extraction Transferable to garlic or fruit waste Fi: onion oil flavour Brose (1993)

Orange and mango skin,

apple pomace, wheat bran

M: grinding, powdering, P: dry-

ing

New technology in dietary fibre production Fi: General application for dietary fibre

enhancement

Larrauri et al. (1999)

Orange peel M: washing followed by leach

liquid treatment, B: pectinolytic

enzyme treatment to recover

soluble solids

Wastewater treatment concept for the pectin

production industry. Material balance de-

veloped

O: pectin wastewater treatment El-Nawawi and Heikal (1996)

Orange peel M, P: cutting, drying, grinding Dye removal with cellulosic material, pa-

rameters: initial conc. of dye important,

particle sizes of adsorbent, pH-value

Op: dye removal in wastewater treatment Namasivayam et al. (1996)

Palm kernel husk M, C Pb is preferably adsorbed to Zn Op: alternative bioadsorbents for wastewater

treatment

Omgbu and Iweanya (1990)

Palm oil mill waste – Quantities and potential usage O: empty fruit bunches for mushroom cul-

tivation, decomposed rest as fertiliser, Op:

palm press fibre for pulp and paper, Op:

palm kernel shell as activated carbon

Prasertsan and Prasertsan (1996)

Peanut and walnut shells – Rich in tannin, possible use in wastewater

treatment

O: heavy metal ions removal in wastewaters Randall et al. (1974)

Peanut skin M, C Stirred tank and packed bed investigations,

two types untreated and treated peanut skin

Op: alternative bioadsorbents for wastewater

treatment

Randall et al. (1975)

174

G.Laufen

berg

etal./Bioreso

urce

Tech

nology87(2003)167–198

Page 9: Vegetal Waste

Pear and kiwi pomace C, M Major analysis of several compounds Fi: sugar source, fibre enhancement insolu-

ble/soluble, pectin

Martin-Cabrejas et al. (1995)

Pineapple cannery waste P: heat treatment, M: centrifu-

gation, B: ethanol fermentation

Continuous fermentation substrate, high

syrup reduces fermenter size, enhances

ethanol production

Op: liquid fuel production Nigam (1999)

Pineapple peel B: SSF Aspergillus foetidus ACM

3996

Substrate is superior to rice or wheat bran,

16.1 g citric acid per 100 g dry waste: 62.4%

yield

Fi: citric acid, O: pharmaceuticals Tran and Mitchell (1995)

Potato peel M, P Baking experiments showed that potato peel

is superior to wheat bran in minerals content,

water holding capacity and lack of phytate

Fi: bread fibre improvement Toma et al. (1979)

Potato starch waste, carrot

pomace

M, P, B Potato fruit water: protein content, peel and

pulp: fibre content, especially soluble frac-

tion, carrot pomace: colour stabilisation,

nutritional value, preservation, viscosity

Fi: multifunctional ingredient in general,

focus on bread and beverages

Laufenberg et al. (1996)

Spent malt B: Ceratocystes fimbriata Good utilisation potential for the formation

of bioflavours even without precursors, sub-

strate screening with several waste types was

done

Fi: general application, O: pharmaceutical

industry

Fischbach et al. (2000)

Sugar beet pulp, cereal

bran

M and P: free ferulic acid from

pectin, B: SSF with two micro-

organisms

1. A. niger to transfer ferulic into vanillic

acid, 2. Pycnoporus cinnabarius into vanillin

Fi: vanillin as a food flavour, O: flavour

compound for chemical use

Asther et al. (1997)

Sugar beet pulp P, C, B Special attention to exploit the hemicellulotic

fraction, gum arabic substitute and fat

replacer has been developed

Fi: dietary fibre, esp. soluble. Two novel

food ingredients were developed, FF: en-

zymes for use in feeds

Broughton et al. (1995a,b)

Sugar beet pulp C: washing with ethanol,

P: drying, M: milling

Coarse (600 lm) and medium (355 lm)

particle sizes showed good cookie properties.

Corn grids gave better colour. In sensory

evaluation cookies with up to 6% sugar beet

were even favoured against plain cookies

Fi: dietary supplement in cookies K€ooksel and €OOzboy (1999)

Sugar beet pulp C, M, P: saponification or pre-

treatment with formaldehyde or

epichlorohydrin

Due to the pre-treatment increasing ion-

exchange capacities and reduced hydration.

Epichlorohydrin treatment seems to be most

efficient, even if sorption/desorption cycles

are suggested

Op: heavy metal removal in wastewater

treatment

Dronnet et al. (1997, 1998a,b)

Sugarcane bagasse, bark

and onion skin

M, C Stirred tank and packed bed investigations,

seven heavy metals tested

Op: alternative bioadsorbents for wastewater

treatment

Kumar and Dara (1982)

Sugarcane bagasse C: lignin extraction Parameters: pH-value, ionic strength, temp. O: heavy metal bioadsorbent for wastewater

treatment

Peternele et al. (1999)

Sugarcane bagasse, pecan

shells

P, P, C: grinding, pyrolysis,

phosphoric acid activation

Comparable efficiency to commercial acti-

vated carbons in decolourisation of raw

sugar

Op: GACs Ahmenda et al. (2000a,b),

Pendyal et al. (1999)

Sunflower heads – Pectin extraction Fi: stabiliser, thickening agent, gelling agent,

soluble fibre

Wang et al. (1997)

Tomato pomace M: grinding, B: fungal cultures,

pure and mixed

Increasing the protein and lignin content,

hence digestibility by micro-organism cul-

tures

Ff: feed stuff or fodder enhancement Carvalheiro et al. (1994)

Tomato skins and seeds P: drying, C: extraction Proteins, minerals, and dyes (lycopenes) Ff, Fi: biocolorants Al-Wandawi et al. (1985)

Urban organic waste B: mesophilic fermentation Volatile fatty acids as possible flavours Fi or O: chemical industry Sans et al. (1995)

G.Laufen

berg

etal./Bioreso

urce

Tech

nology87(2003)167–198

175

Page 10: Vegetal Waste

the influence on colour stability an application of thelatter ascorbic acid would be most useful for food app-

lications.

Hence almost any recycling process will start with the

steps pre-treatment (ensiling), drying, size deduction and

fractionation.

The overall recycling strategy, described in Fig. 3, is

designed in a modular manner, thus subdivided into

substance characterisation, definition of objectives,product and process design and application and opti-

misation. The result is a final product which is opti-

mised, in regard to the requested product properties, in

the exhibited way a multifunctional food ingredient.

The first phase is mainly the substance characteri-

sation, based on these data the optimal recycling and

application areas and possibilities are worked out. Par-

ticle classification, chemical analysis and physicochemi-cal properties are the important steps.

Following the definition of objectives will enclose the

desired properties of the future food ingredient as well

as the food to be applied to. At this point a decision has

to be made about the use in theory. Based on these ‘‘key

properties’’ advantages will arise for technological ben-

efit, health or taste of a product.

Product and process design covers product and dis-persion properties as well as their changes depending on

the process parameters. Obvious examples are desirable

or undesirable interactions between the food ingredients

in general or during processing and interactions with

surrounding and processing factors.

The range of possible interactions is enormous, thus a

concentration on the valuable ingredients as well as on

the desired technological, sensorial and physiologicalproperties is useful. A continuous control and improve-

ment of the upgrading process and product can be

gained by prototype development, definitions of partial

qualities as well as incorporation of feed back circles.

At the application phase food product and newly de-

signed food ingredient will be combined. At this inter-

action point the estimated use and practical application

in a real food system meet each other. Quality relatedproperties of the new product have to be assessed and

compared with similar products being already on the

market. Hence a successful launch may be forecasted.

The sensorial quality is the most important criteria

for a multifunctional food ingredient applied in a new

product. Since sensorial, technological and nutritional

quality of the new product is compared to a so-called

‘gold standard’, the optimisation is nearly completed.Final investigations into product properties will answer

questions, which are useful to point out the consumers’

benefit or even the unique selling position. The latter is

often science based and hence measurable.

Instead of producing a multifunctional food ingredi-

ent the goal could be alternatively the bioconversion

into a food flavour or the development of an operationalTable

3(continued)

Residualmatter/co-product

Pre-treatm

ent

Results

Application/secondary

use

Reference

Vanilla

shells

CO

2flavourextraction

Patent

Fi:Naturalvanilla

flavour

Schutz

etal.(1982)

Vegetable

raw

materials

–O:bioplasticswithspecialproperties

Feil(1995)

Vegetable

residues

(not

specified)

M,P,B

Porouscarbohydrate

ingredientswithcarrier

functionto

encapsulate

flavours

Fi:dietary

fibre

enhancement,flavouren-

capsulationandapplicationin

variousfood

Zeller(1999)

Vegetable

waste,

24types

–Analysisofthenutritivepotential,cauli-

flower

leaves

bestnutritivescore

Ff:forruminants

Gupta

etal.(1993)

Wheatbran

M:debranning,polishing

Fi:multifunctionalfoodingredientwith

specified

physicochem

icalandnutritional

properties

DexterandWood(1996)

Wheatstraw,corn

stalks

B:biodegradationofhem

icellu-

losicfractionbyL.edodes

SSFissuperiorto

SMFforbiodegradation,

mechanicalcharacteristics

ofthepaperswere

improved

Op:paper

andpulp

fibre

resource(lignin)

Giovannozzi-Sermanniet

al.

(1995)

Wheatstraw,insoluble

straw

xanthane

M:grinding,C:alkalitreatm

ent

>90%

removaleffi

ciency

inheavymetal

solutions,75–95%

intannerywastew

ater

Op:wastew

atertreatm

entadsorbent

Kumaret

al.(2000)

Woolfibre

M,P:washing,drying,C:

petroleum

ether

degreasing

Parameters:fast

rate

uptake,

notemp.

dependency

Op:heavymetalcationsremovalin

waste-

watertreatm

ent

Balk€ oose

andBaltacioglu

(1992)

C:chem

ical,M:mechanical,P:physical,B:biotechnical;Ff:fodder/feed,Op:operationalsupply,Fi:foodingredient,O:other

and(–):nodata

available.

176 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 11: Vegetal Waste

supply like a bioadsorbent. Hence different objectives

will affect the product and process conception and the

application phase.

In the following the theoretical description of theupgrading concept will be verified at three implemen-

tation examples.

Part B

4. Target state: Selected practical implementations

4.1. Novel types of products: multifunctional food ingre-

dients

Let your food be your first medicine

(Hippocrate, 377 B.C.)

A promising possibility for the utilisation of organicresidues in the frame of green productivity is the de-

velopment of innovative products. In the mentioned

context multifunctional food ingredients have to be

understood as natural ingredients taking over food ad-

ditive functions during processing and/or add a further

benefit to the final product.

Several research groups have been working on thedevelopment of multifunctional ingredients from vege-

table residues and its application in different food

products. The crude fibre content combined with at least

one other property enables them to fulfil several func-

tions in food as exhibited in Table 4. A couple of quality

Fig. 3. Strategy for the development of multifunctional food ingredients made of vegetable residues: the upgrading concept (modified after Henn

(1998)).

Table 4

Food properties and quality influenced by multifunctional food in-

gredients (Laufenberg et al., 1996)

Operating areas of multifunctional food ingredients due to food

properties and quality

(1) Nutritional and healthy quality, e.g. vitamin content, dietary

fibre content

(2) Food product structure, e.g. porosity, network structure

(3) Sensorial properties, e.g. texture/structure, mouth feel, freshness

(4) Physical properties, e.g. density, viscosity

(5) Processing properties, e.g. water binding ability, emulsifying

properties

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 177

Page 12: Vegetal Waste

determining food properties can be governed by theapplication of these food ingredients. The raw material

mostly used is carrot pomace (Filipini and Hogg, 1997;

Henn and Kunz, 1996; Henn, 1998; Lucas et al., 1997;

Ohsawa et al., 1994;Ohsawa et al., 1995; Laufenberg et al.,

1996), followed by citrus waste (Sreenath et al., 1995;

Widmer and Montanari, 1995), grape or apple pomace

(Borycka, 1996; Carson et al., 1994; Lucas et al., 1997;

Saura-Calixto, 1998; Masoodi and Chauhan, 1998),sugar beet pomace (Broughton et al., 1995a,b; K€ookseland €OOzboy, 1999), orange, mango and apple peel

(Larrauri et al., 1999), mango kernel flour (Arogba,

1999) (as a wheat flour substitute), potato peel (Toma

et al., 1979), sugarcane bagasse (Clarke, 1995) or mix-

tures of oat, rice, corn hulls and pea pods (Inglett, 1998).

They are applied in pie fillings (Carson et al., 1994),

crackers (Carson et al., 1994; Joshi and Sandhu, 1996),bread (Filipini and Hogg, 1997; Lucas et al., 1997;

Ohsawa et al., 1994; Clarke, 1995), cookies (Clarke,

1995; K€ooksel and €OOzboy, 1999), beverages (Henn and

Kunz, 1996; Henn, 1998; Laufenberg et al., 1996; Sree-

nath et al., 1995), jam (Grigelmo-Miguel and Martin-

Belloso, 1999), and cakes, dressings and pickles (Ohsawaet al., 1995). New approaches try to use the dietary fibre

as a matrix for the encapsulation of antioxidants (Saura-

Calixto, 1998) or flavours (Zeller, 1999), using both the

physiological effects and the technological advantages in

the form of a controlled release.

Almost every flavour company is nowadays inter-

ested in microscopically encapsulated aromas, which do

not escape directly but under precisely defined circum-stances, for example under mechanical stress such as

chewing the chewing gum or at a certain temperature

while baking cake mixtures (Stock, 1999; Schr€ooder,1999).

Beside the application as a texturing or gelling agent

the fat replacement function in diet food is an impor-

tant advantage of fibres. Recently new food additives

have been developed on the basis of vegetable residues(Broughton et al., 1995a,b; Inglett, 1998).

The high crude fibre content of the vegetable po-

mace, see Table 5, suggests its utilisation as a crude

fibre ‘‘bread improver’’. One reason for the low di-

etary fibre uptake is the non-acceptance of whole meal

Table 5

Content and composition of dietary fibre of some residues (Laufenberg et al., 1996; Martin-Cabrejas et al., 1995; Torre et al., 1995; Seibel and

Hanneforth, 1994)

Residues Fibre Pectin Lignin Cellulose

Total Insoluble Soluble

Apple pomace 62.5 48.3 14.2 15.69 18.2 –

Barley pomace 65.3 62.1 3.2 – – –

Carrot pomace 29.6 18.9 10.7 22–25 – –

Cocoa pod husks/bean

shells (Nambudiri and

Shivashankar, 1985)

36.3 – – 6 – 13.7

Corncobs – – 43a – 17 (Hawthorne Costa

et al., 1995)

32

Kiwi pomace 25.8 18.7 7.1 7.25 3.2 –

Lemon peel 50.9 28.2 22.7 25.23 5.5 –

Lemon pulp 45.8 26.0 19.8 12.02 2.9 –

Olive cake 69.4 65.7 3.7/15.5 (Haddadin

et al., 1999)a4.10 37.2/35.4 (Haddadin

et al., 1999)

18.4 (Haddadin et al.,

1999)

Pea pots 90.1 84.7 5.4 – – –

Peach pomace (Pag�aan

and Ibarz, 1999)

54.5 35.4 19.1 – – –

Pear pomace 43.9 36.3 7.6 7.05 5.2 –

Potato peel (Toma

et al., 1979)

73 6.2a 16 13.8 16

Potato pulp 15.8 9.4 6.4 �15 (Tuncel et al.,

1998)

– –

Soybean shells 64.6 56.9 7.7 – – –

Sugar beet pulp 75.3 50.1 25.2/22.1 (K€ooksel and€OOzboy, 1999)

30 (Purchase, 1995)/26

(Broughton et al.,

1995b)

1.85 (K€ooksel and€OOzboy, 1999)/4.56

(Broughton et al.,

1995b)

23/27.2 (K€ooksel and€OOzboy, 1999)

White wine pomace 58.6 56.3 2.3 3.9 (Torre et al., 1995)/

5.5 (Valiente et al.,

1995)

41.2 (Torre et al.,

1995)/53.6 (Valiente

et al., 1995)

Results expressed as percentage of original dry matter, (–): no data available.aAs hemicellulose.

178 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 13: Vegetal Waste

products in large parts of the population. An enrich-ment of different products with crude fibre compounds

can thus raise the dietary fibre uptake, if the food

products are not modified too much. The macro-

molecular structure of the fibre must not be changed

during the transformation of the residue into a food

compound, and the fibre material has to be of food

grade.

In bread and bakery goods, as well as in pastry, ce-reals and dairy products, the investigated carrot pomace

works as a stabiliser. Beside crude fibre it is rich in pro-

vitamins, colour and natural acids. It takes over several

functional properties mentioned in Table 4, additionally

substitutes sourdough in bread, is acidifying agent,

preservative or antioxidant in several food products

(Filipini and Hogg, 1997; Lucas et al., 1997; Ohsawa

et al., 1994, 1995; Toma et al., 1979; Masoodi andChauhan, 1998).

In beverages, carrot pomace or citrus waste will sta-

bilise the natural colour, improve the vitamin and fibre

content, enhance the viscosity (mouthfeel) (Laufenberg

et al., 1996; Henn and Kunz, 1996; Henn, 1998), and

enrich or adjust the cloudy appearance (Sreenath et al.,

1995). The organoleptic and chemical properties offer a

widespread use in healthy and functional drinks andselected fruit juices.

Several series of experiments were done to determine

the influence of different pre-treatment/preservation

methods on the physicochemical properties of carrot

pomace when applied in food. Therefore common

acidifying agents, i.e., citric, acetic or ascorbic acid, were

applied to stabilise and preserve the fresh pomace, as

well the carrot pomace was fermented by Lactobacillus

farciminis.

Processing of the vegetable residue can be done by

fermentation with lactic acid bacteria leading to a

suitable transformation of low molecular materials

like sugars and to a microbial stabilisation, because

enterobacteriaceae and moulds present on the po-

mace are inhibited by the lactic acid formed. Thiseffect is already used for several vegetables in-

cluding carrots with the task of preservation, e.g.

pickles. The pomace is fermented by Solid-State-

Fermentation, which does not need as much free

liquid phase as submerged fermentation and thus

makes downstream processing of the crude fibre

product easier and cheaper. After lactic acid fer-

mentation of carrot and grape pomace the productis rich in crude fibre, shows an acidic pH and can be

used as a bread improver and for crude fibre enrich-

ment of bakery goods.

Afterwards the pomace was treated with common

drying operations, i.e., spray, freeze or oven drying. It

could be determined that the colour stability was mostly

improved by the addition of ascorbic acid (avoids the

formation of free radicals), which improves the nutri-

tional value too. Fermented samples were superior to

non-fermented samples as clouding agents and showed agood shelf life too.

The ideal dietary fibre should meet specific require-

ments, residues own natural properties, this relation

could be tailored during the different processing steps, as

exhibited in Fig. 4.

Currently there is a great variety of raw materials

from which dietary fibres are obtained such as wheat

or rice, etc. Useful alternatives/substitutes could begained from vegetable residues like orange peels, mango

peels, grains, soybean or oat hulls, cereal bran, etc.

(Larrauri et al., 1999), fruit pomace (Borycka, 1996),

grape pomace (Martin-Carron et al., 1997; Valiente

et al., 1995), pear and kiwi pomace (Martin-Cabrejas

et al., 1995), wheat bran (Dexter and Wood, 1996), or

sugar beet pulp (Broughton et al., 1995a,b; K€ooksel and€OOzboy, 1999).

Several treatments could be performed to improve the

functionality of the insoluble fibre, which is the main

component of the residual matter, mentioned in Table 5,

as

Fig. 4. Natural properties of vegetable waste (average) and food properties and quality being influenced by multifunctional food ingredients.

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 179

Page 14: Vegetal Waste

• partial delignification of lignocellulose by alkalineH2O2 treatment,

• extrusion,

• encapsulation with soluble fibre to produce a product

with better textural properties,

• enzymatic modification to improve sensorial proper-

ties.

Dietary fibre from cereals are more frequently usedthan those from fruits, although fruit fibres have better

quality due to higher total and soluble fibre contents,

lower phytic acid contents, colonic fermentability and

water and oil holding capacities. The latter is of par-

ticular interest for the carrier function of dietary fibres

which has been already used for antioxidants (Saura-

Calixto, 1998), encapsulation of flavours (Zeller, 1999)

or dyes (Filipini and Hogg, 1997; Henn, 1998). There isa future need to develop processes for the preparation of

fruit fibres that minimise the losses of associated natural

bioactive compounds which may exert higher health

promoting effects than the dietary fibre itself. The higher

concentration of health promoting flavonoids compared

to traditional wine growing is often mentioned in con-

nection with ecological viniculture. Besides environ-

mental benefits the quality of the wines is improved,resulting in higher prices for these wines and special

recommendations in wine guide journals (Kriener,

1999).

Saura-Calixto (1998) produced a dietary fibre rich in

associated polyphenolic compounds combining in a

single material the physiological effects of both dietary

fibre and antioxidants. Fibre matrices could act as

support for biocolourants made of anthocyanins fromolive cake (Clemente et al., 1997), lycopenes from to-

mato skins (Al-Wandawi et al., 1985) or b-carotenefrom carrot pomace (Henn and Kunz, 1996). Phenolic

compounds are powerful antioxidants and may possess

potential pharmacological properties, already widely

used with green tea catechins (Nwuha et al., 1999) or

ferulic acid extracted from sugar beet pulp (Couteau and

Mathaly, 1998) which could make them desirable in-gredients in the developing market of ‘functional foods’

for health. Bioflavonoids like hesperidin, naringin or

rutin are able to normalise capillary permeability and

vascular brittleness, therefore they are frequently called

vitamin P factors. Hesperidin is applied in vein medi-

cation, acts antiviral in flue therapy and owns artificial

sweetener properties; hydrated naringin is �300 times

Table 6

Content of several relevant compounds in vegetable residues (Al-Wandawi et al., 1985; Clemente et al., 1997; Henn, 1998; Larrauri et al., 1999; Lu

and Foo, 1997; Saura-Calixto, 1998)

Residue Plant phenols (flavonoids, phenol carboxylic acids)

Colourless Coloured

Apple pomace 0.724%a (Lu and Foo, 1997); 350.6 mg/kgb, FA 8.0 mg/kgb

(Lucarini et al., 1999)

Carrot pomace b-carotenea 3 mg/kg

Chokeberry

pomace

Anthocyanins 9.1 g/kg (M�aari�aassyov�aa et al., 1999b)

Cocoa bean shells Tannins 3.1%a Leucoanthocyanidin (Nambudiri and Shivashankar, 1985)

Elderberry pomace Anthocyanins 16.6 g/kg (M�aari�aassyov�aa et al., 1999b)

Grape pomace 2%a; 11.7%a (Zeller, 1999) Anthocyanins

Grape skins 25–35%a (Anon., 1999) Anthocyanins

Grape fruit peel Naringin 0.07–1.7%b Carotenoids

Green tea 10.1–21.6%a ;c

Honeysuckle

pomace

Anthocyanins 8.0 g/kg (M�aari�aassyov�aa et al., 1999b)

Mango peel 5.5%a Carotenoids

Olive press cake 0.3%b Anthocyanins

Orange peel Hesperidin 1.3–2.4%b/1.7–2%a (Manthey and Grohmann,

1996); Nobiletind 32% (Manthey and Grohmann, 1996)

Carotenoids

Red beet pomace Betanine 414.3 mg/kgb (M�aari�aassyov�aa et al., 1999a)

Sugar beet pulp FA 0.36%a (Couteau and Mathaly, 1998)/8 g kga

(Thibault et al., 1998)

Tomato skins 210.8 mg/kgb FA 3.7 mg/kgb (Lucarini et al., 1999) Lycopenesb 120 mg/kg (Al-Wandawi et al., 1985), 80 mg/kgb

(Lucarini et al., 1999)

FA¼ ferulic acid.aRelated to dry mass.bRelated to fresh good.cDepending on the tea species and seasonal changes. Tea flavonoids are catechin, gallocatechin, epicatechin, epicatechin gallate, epigallocatechine,

epigallocatechin gallate, the latter of which is always the largest fraction (Chu and Juneja, 1997).d In orange peel oil solids (hexane extracted).

180 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 15: Vegetal Waste

sweeter than saccharose, neohesperidin almost 2000times.

The array of different compounds existing in a di-

versity of free and bound forms is considerable, see

Table 6. Grape skin extract in powder form is com-

mercially available as a natural food colorant. Besides

the blue–red colour the food will be enriched with

‘‘healthy’’ polyphenols (Anon., 1999). The fermentation

of dietary fibre increases digestibility, shelf life andpreserves the bioactivity of the components. It is often

recommended as a hygienisation step prior to drying

and milling (see above).

The use of fibres from new origins that are cur-

rently not fully exploited and the possibility of mod-

ifying the fibres, by chemical, enzymatic and/or

physical treatments, combining them with other com-

ponents and enhancing their nutritional and sensorycharacteristics, will probably widen the fields of ap-

plication for dietary fibres. Thus this market shows a

reasonable utilisation potential for vegetable residues,

adding value to by-products, most of which are re-

garded as waste to be discharged so far (Theobaudin

et al., 1997).

Several residues have already been characterised by

their pectin content, as shown in Table 5. Pectins arelinear polymers of a-DD-galacturonic acid in which the DD-

galacturonic acid units are linked by 1 ! 4 glycosidic

linkages. Pectic substances have an important influence

on food texture and are used in products like jams, jel-

lies, dairy products, beverages, pastries and confection-

eries. More and more they are used in pharmaceutics

and cosmetics as well. Pectin is located in the cell walls

of vegetables and fruits, commercially and environ-mentally interesting is the use of residual matter as

a potential pectin source. The gelation mechanism of

pectins is mainly governed by their degree of esterifica-

tion (DE). Commonly, two types of pectin gels are dis-

tinguished. The first type made from high methoxyl

pectins (DE beyond 50%) form gels in an acidic envi-

ronment and in the presence of sucrose. The second type

of pectin gel is composed of low methoxyl pectins (DEbelow 50%). These pectins form gels in presence of al-

kaline earth elements, especially calcium. In both cases

gelation and gel properties depend on many factors,

including pH, temperature, DE, sugar, calcium, and

pectin content (Tuncel et al., 1998).

The presence of up to 30% pectin in dried residual

matters like sugar beet pulp, carrot pomace, potato pulp

or lemon peel and its availability in large quantities havemade extraction worthwhile. Several other sources of

pectin are reported beside the mentioned ones in Table

5, e.g., citrus peel (Widmer and Montanari, 1995), cit-

rus, apple and sugar beet pulp (Grohmann and Bothast,

1994), cocoa husk (Nambudiri and Shivashankar, 1985),

galgal (citrus fruit) peel (Attri and Maini, 1996), haw-

thorn (Mexican fruit) peel (Higareda et al., 1995),

mango peel (Srirangarajan and Shrikhade, 1976) orsunflower heads (Wang et al., 1997).

However, no pectins have ever been extracted

from vegetable residues with gel forming proper-

ties comparable to those of pectins extracted from

apple pomace. Turqouis et al. (1999) recently developed

an alkaline extraction process for pectin from sugar

beet pulp and potato pulp. A high gelling ability

was proved using 2% extract from sugar beet and po-tato pulp with 172 mg CaSO4 H2O per g extracted

product.

Kahlert (1999) tried to overcome the low gelling

properties by the combination of gelling agents using

their synergetic effects. A lot of structuring substances

like cellulose, pectin, carrageen, agar-agar, alginate can

be taken from vegetable waste and composed to new

multifunctional food ingredients and act as stabilisers,thickeners, fat replacement, etc. Pectins of different or-

igin could be mixed due to the requested application and

properties, examples are mentioned in Higareda et al.

(1995), Nambudiri and Shivashankar (1985), Srirang-

arajan and Shrikhade (1976), Wang et al. (1997) and

Widmer and Montanari (1995).

4.2. Bioconversion via solid-state fermentation: the gen-

eration of flavours

The tongue cannot be betrayed permanently.

(K€ooster, E. International FoodTec Congress,

Cologne/D 1994, giving a lecture about natural

and synthetic food additives.)

Biological conversion processes of fruit processing

wastes into various value added products through solid-

state fermentation (SSF) has been of major interest to

many laboratories around the world. SSF deals with theutilisation of water-insoluble materials for microbial

growth and metabolism, and it is usually carried out in

solid or semi-solid systems in the near absence of free

water or reduced water content compared with sub-

merged fermentation (SMF). Many of the potential

products from fruit and vegetable residues have been

developed using the SSF technique, and such products

include ethanol, methane, lactic acid, citric acid, mush-rooms, enzymes and food ingredients (Zheng and

Shetty, 1998). As shown in Table 9 most of the research

in SSF of residual matter has been done in the last seven

years. Still there is a lack of proper modelling and

process parameters.

The world market of aroma chemicals, fragrances

and flavours has world-wide a growth rate of 4–5% per

year. In 1995 it was worth 9:6� 109 US$ and in 2000it is expected to be 12� 109 US$ (Hartman, 1996).

Because of a higher consumer acceptance there is an

increasing economic interest in natural flavours.

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 181

Page 16: Vegetal Waste

The European Community guidelines 88/388/EWGand 9/71/EWG subdivide flavours/aromas into six

categories, the first of which is describing regula-

tions for the food labelling ‘‘natural flavour’’. Nat-

ural flavours are chemical substances with aroma

properties which are produced from feedstock of

plant or animal origin by means of physical, enzy-

matic or microbiological processing (Huber and

Fo�aa, 1999).

The microbial synthesis of these natural flavours is

generally carried out by SMF. Due to the high costs of

this currently used technology on an industrial scale

there is a need of developing low cost processes even forcheaper molecules like benzaldehyde (�US$ 198 per kg

(Sigma, 2000)). This could be achieved by exploration of

the metabolic pathways and by alternative technology

such as SSF (Feron et al., 1996).

Suitable for SSF is every vegetable waste in principle.

In case of bioflavour production the SSF of residual

matter is a fairly new technology of waste utilisation,

based on a very old preservation method, which bio-converts secondary raw materials to natural flavours, as

shown in Table 11.

The microbial synthesis on solid substrates offers

some advantages compared with conventional SMF

such as

• The conditions of the SSF-process are well adapted

to the requirements of moulds, which represent about60% of the micro-organisms used in flavour produc-

tion.

• The higher space-time yield leads to smaller reactor

volumes compared with SMF. The SSF reactor with

the same yield as an SMF reactor can lead to a three

times smaller amount of investment costs (Vollbrecht,

1997).

Most important flavour is currently vanillin, the an-

nual world-wide use exceeds 12,000 t/a, 20 t of which are

produced from natural extract (equivalent to 1800 t of

vanilla beans) (Asther et al., 1997). Vanillin is followed

by benzaldehyde, used in an amount of more than 1000

t/a. Vanillin is currently synthesised from petrochemical

substances like guajacol, or lignin, both of which are

produced as co-products of pulp manufacture in huge

amounts. The microbiological production is based on

the precursors eugenole or ferulic acid, the latter oftenfound in vegetable residues and pomaces in reasonable

amounts. So far there are only few effective bioconver-

sion processes available, hence an industrial application

is limited.

Tables 7 and 8 are an overview of profit margins

possible provided that an effective production path is

found. Table 9 lists recent progress in SSF of vegetable

residues, obviously most research in flavour fermenta-tion via SSF was done in the last seven years.

In order to introduce an economically competitive

biological process, three major drawbacks must be

overcome:

II(I) The high costs of the substrate (e.g., molasses).

I(II) The low product concentration (about 2% for ace-

tone–butanole–isopropanole (ABI) fermentationbecause of solvent toxicity).

Table 7

Selected flavours, production rates and selling prices

Flavour Feed conc.a Selling price in US$/kg Year

Vanillin 230 mg/l (Asther et al., 1997) Natural extract 4000 (Asther et al., 1997) 1996

560 mg/l (Thibault et al., 1998) 1998

c-Deca lactone 6 g/l Biotechnical 6000 1992

Isoamyl acetate 5.22 mg/kg DM 1999

6.25 mg/l (Christen et al., 1997) 1997

b-Phenethyl alcohol 2 g/l Biotechnical 2500 1994

2-Heptanone 17 g/l Synthetic 39 1991

Ethyl butyrate – Biotechnical 180 1996

(–) No data available.aRelated to biotechnical production.

Table 8

Selected flavours and selling prices in US$ per kg

Flavour/aroma Description Synthetic Natural

c-Deca lactone Peach, fruity 75.00 1400.00

d-Deca lactone Coconut, creamy 130.00 5500.00

1-Octen-3-ol Mushroom 184.00 –

2-Heptanone Cheesy, spicy 39.00 –

Benzaldehyde Almond 31.00 198.00

Ethyl butyrate Fruity, pineapple 31.00 55.00

Isoamyl acetate Banana, fruity,

sweet

31.00 31.00

Isoamyl butyrate Banana, fruity,

pineapple

31.00 345.00

Phenethyl alcohol Roses 31.00 2050.00

Raspberry ketone Raspberries 58.00 3000.00

Vanillin Vanilla 31.00 685.00

Vanillic acid Vanilla 410.00 –

Source: Flavors & Fragrances 2000, Aldrich Milwaukee WI USA,

(Sigma, 2000).

182 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 17: Vegetal Waste

(III) The high product recovery costs (distillation hasbeen used in the past).

The provision of substrates makes up about 63% of

the total costs of ABI production, therefore a variety of

alternative compounds have been checked out for their

ability to replace the now expensive molasses (Duerre,

1998). The high raw material costs could be drastically

reduced by using vegetable co-products as substrates,see Table 9. Christen et al. (2000) mixed various pro-

portions of vegetable residues and added selected

precursors to additionally influence metabolism and

product concentration. They found that the volatile

carbon production by fungi can be significantly influ-

enced, leading to manifold enhanced production rates.

Remaining problem besides the production of a cer-

tain flavour is its isolation and purification (downstream processing), which is again strongly dependent

on the produced concentration of the ‘‘biochemical’’.

Therefore research groups have been looking for com-bined solutions of highly concentrated production and

on-line separation (Kunz, 1999).

A pilot plant for acetone and butanol fermentation in

Starrein/Austria is described in (Duerre, 1998), the op-

erational start was planned for spring 1998. As sub-

strates have been used agricultural ‘starchy’ materials

like low grade potatoes, potato cutting waste, potato

pulp and fruit water from starch production, maize andrye. The product separation is done by gas stripping

with heating of the effluent to �70 �C and condensation

of the solvent/water vapours.

Membrane based systems such as reverse osmosis,

perstraction, pervaporation and membrane evaporation,

as well as liquid/liquid extraction, adsorption and gas

stripping have been compared by Duerre (1998) towards

their employment in downstream processing, but thereis no precise statement as to the most suitable one.

Membrane systems show a high selectivity for solvents,

Table 9

Flavours and biofine chemicals produced by SSF of vegetable residues (selection)

Year Residual matter Description/conversion principle Product

1991 Apple pomace (Almosnino and Belin, 1991) Enzyme system to degrade the precursors

linoleic and linolenic acid

Volatile aldehydes, alcohols

2000 Apple pomace, spent malt grains (Stredan-

sky et al., 2000)

T. elegans CCF 1456 degraded the substrate

in a ratio of 3 to 1 (AP to SMG), precursor

peanut oil even increased the yield

c-Linolenic acid was produced in a yield of

5.17 g per kg dry substrate; with peanut oil

precursor 8.75 g per kg DM

1998 Carrot, citrus, pineapple pomace (Mukher-

jee and Sen, 1998)

Aspergillus spp. Mass multiplication Biocontrolling agent in cultivation of mel-

ons

2000 Cassava bagasse, apple pomace (Christen

et al., 2000)

Four strains of Rhizopus, two residues and

two precursors, mixed substrate combina-

tions

Volatile carbons as flavours; acetaldehyde,

ethanol, propanol, esters

1997 Cassava bagasse, wheat bran and sugarcane

bagasse (Christen et al., 1997; Bramorski

et al., 1998)

C. fimbriata, ability to generate fruity aro-

mas in dependence on the substrate used

Banana flavour and fruity complex flavours,

up to 10-fold higher production compared

to ripe bananas

1994 Citrus, apple, sugar beet pomace (Groh-

mann and Bothast, 1994)

Microbial conversion by enzymatic hydro-

lysis

Pectin, substrate, liquid biofuel

1998 Cranberry pomace (fish offal) (Zheng and

Shetty, 1998)

Trichoderma viride, Rhizopus CaCO3 was

added as neutraliser, water for aw adjust-

ment

Polymeric dye decolourising isolate for

wastewater treatment, extracellular enzymes

2001 Linseed cake, castor oil cake, olive press

cake, sunflower cake (Laufenberg et al.,

2001)

Moniliella suaveolens, Trichoderma harzia-

num, Pityrosporum ovale and Ceratocytis

moniliformis form decalactones (problems

with phenolic components)

Acceptable yields on olive press cake and

castor oil cake. d- and c-decalactone (up to

1 g per kg DM) are produced

1998 Olive cake, sugarcane bagasse (Cordova

et al., 1998)

Lipase degrading fat in olive cake Enzyme product applied in bakery goods,

confectionery, pharmaceuticals

1999 Olive pomace (Haddadin et al., 1999) Four micro-organisms, delignification, sac-

charification with Trichoderma spp., bio-

mass formation with Candida utilis and

Saccharomyces cerevisiae

Crude protein enriched from 5.9% to 40.3%.

Source for animal fodder

1995 Pineapple waste (Tran and Mitchell, 1995) A. foetidus produces citric acid 16.1 g/100 g

DM and 3% methanol

Pharmaceuticals, food industry, preserving

agent

1997 Potato waste (Lucas et al., 1997) Amylases Bakery goods, breweries, textile industry

1997 Sugar beet pulp, cereal bran (Asther et al.,

1997)

Commensalism of two micro-organisms de-

grading the substrate

Flavour vanillin

1994 Tomato pomace (Carvalheiro et al., 1994) Co-cultures of Trichoderma reesei and

Sporotrichum sp. are degrading cellulose and

hemicellulose fraction

67% less cellulose, 73% less hemicellulose,

enhanced lignin and protein content

DM ¼ dry matter.

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 183

Page 18: Vegetal Waste

but might suffer from clogging and fouling, liquid/liquidextractions might form emulsions, reducing their effec-

tiveness, gas stripping does not lead to complete removal

of solvents and adsorption materials are quite expensive.

The raw material costs for the latter adsorption mate-

rials could be drastically reduced by the use of bioad-

sorbents made of vegetable waste, which is explained in

detail below.

The restrictions might be overcome by the com-bination of SSF with hollow fibre contained liquid

membranes for the production and separation of vola-

tile food flavours like isoamyl acetate or 1-octen-3-ol

(mushroom), recently described in Laufenberg and

Cussler (1999).

The bioconversion of vegetable residues is economi-

cally attractive only if high value products are produced.

The market prices for biotechnically produced bulkchemicals are fairly low, e.g., 0.53 per kg butanol, 0.44

per kg acetone or 0.40 per kg ethanol (prices in US$ in

1980 (Duerre, 1998)). The selling prices for bioflavours

are many times higher, as shown in Table 8. Highlights

are of course fruity/flowery flavours like peach, rose or

vanilla, but also for banana, produced by Ceratocystis

fimbriata as a complex bioflavour with improved qual-

ity, the fermented flavour will reach higher market pri-ces.

The variety of vegetable residues as substrates could

be even broadened by using co-cultures of micro-

organisms, called commensalism. C. acetobutylicum for

example is unable to degrade cellulose, but in co-culture

with a mesophilic cellulolytic Clostridium spp. even cel-

lulose-enriched rice hulls, orange peel or sugar beet pulp

could be metabolised (Duerre, 1998). The researchgroup of Asther et al. (1997), Bonnin et al. (1999) and

Lesage-Meessen et al. (1999) employed a co-culture of

Aspergillus niger and Pycnoporus cinnabarius to trans-

form ferulic acid from sugar beet pulp via vanillic acid

into vanillin.

Ferulic acid is found associated with the cell wall of

very few dicots, including sugar beets (0.36% related to

dry weight) (Broughton et al., 1995a,b; Couteau andMathaly, 1998) and many monocots like wheat or maize

(1–2% related to dry weight) (Asther et al., 1997; Dexter

and Wood, 1996). It is ester-linked to pectic sidechains

in beets and ether-linked to lignin in cereals. Besides

sugar beet pulp carrot pomace contains of reason-

able amounts of pectin, thus of ferulic acid. For

olive press cake and corncobs a lignin content of �35%

rsp. 17% indicates high precursor rates too, see Table 5;remarkable amounts of ferulic acid are mentioned

for palm press fibre by Prasertsan and Prasertsan

(1996).

Almosnino and Belin (1991) described the use of the

intrinsic enzyme system of apple pomace for the bio-

transformation of fatty acids into potential flavours. By

the use of these lipolytic enzymes the precursors linoleic

and linolenic acid were converted into alcohols andvolatile aldehydes. A possible substrate to use instead of

the precursors would be olive cake with its amounts of

74.0% oleic acid, 11.7% linoleic acid and 0.8% linolenic

acid (Clemente et al., 1997). Thus a mixture of these

residues would result in a useful substrate for a bio-

conversion of flavours. The addition of SO2 and ascor-

bic acid combined with micronization of the pomace

enhanced the flavour yield significantly up to 90%. Theaddition of ascorbic acid may be replaced by a lactic

acid bacterial fermentation of the pomace, which will

enhance shelf life of the pomace and possibly flavour

yield.

A few other studies have shown the importance of the

media in the specific development of a defined aroma

(Christen et al., 1994, 1997; Meza et al., 1998). They

found that adding a nitrogen source enhances the for-mation of total volatiles up to 10 times, which is 10-fold

higher than that of ripe bananas too, as listed in Table

10.

Cassava bagasse with leucine supplement seems to be

the optimal substrate for banana flavour production.

Spent malt appears to be an even better substrate for

total volatile carbon formation. Fermentation with this

substrate has reached almost double production yieldswithout any additional supplement. Biomass develop-

ment and isoamyl acetate formation profiles are shown

Table 10

Isoamyl acetate formation depending on the substrate used (based on

(Christen et al., 1997))

Residual matter Isoamyl acetate formation

in lmol l�1

Wheat bran/no supplement Not detectable

Sugarcane bagasse/no supplement Not detectable

Cassava bagasse/no supplement 0.45

Spent malt/no supplement (Fischbach

et al., 2000)

0.8

Wheat bran plus leucine 2.1

Sugarcane bagasse plus leucine 9.5

Cassava bagasse plus leucine 48

Fig. 5. SSF of spent malt with C. fimbriata (Fischbach et al., 2000;

Laufenberg et al., 1999).

184 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 19: Vegetal Waste

in Figs. 5 and 6. First experiments have shown that

spent malt has a good utilisation potential as a substrate

for the production of fruit flavours. A substrate

screening including spent malt, rape seed oil cake, soy-

bean coarse meal and different kinds of sugar beet pel-

lets and chips was done, where spent malt reached the

highest product yields, see Table 11. Therefore, the

following experiments were carried out using spent maltas an exclusive substrate.

Additional optimisation of the media could be

reached by the combination of spent malt with potato

pulp consisting of remaining 6.1% (w/w) raw protein

(Laufenberg et al., 1996). Further investigations havenot been published yet.

4.3. Vegetable residues as operating supplies: bioadsor-

bents for wastewater treatment

Realising the maximum potential using the mini-

mum amount of material.

To view vegetable waste recovery processes as po-

tential goldmines is typically overly optimistic, as the

costs of extraction and purification of the components

generally reduce the profit margins available to levelsthat are barely economic, as already described. For this

reason further effort is focused on the creation of ‘bio-

adsorbents’ with improved functionality, using their

natural content of adsorptive components or enhancing

their adsorption rate by combination of favoured raw

materials.

Adsorption is almost always a process involving a

fluid and a solid. This solid can adsorb mere traces ofsolute, making this method especially useful for dilute

solutions, including those streams requiring treatment

for pollution control. Molecules adsorb on virtually all

surfaces, the amount they adsorb is roughly propor-

tional to the amount of surface. As a result, commercial

adsorbents are extremely porous with surface areas

typically of several hundred square metres per gram. In

general the energy intensive and sophisticated materialrequiring treatment tends to be more expensive than

other separations.

Adsorbents are conveniently divided into three clas-

ses: inorganic materials, synthetic polymers and car-

bons. Inorganic materials vary widely. Activated

alumina with polar surface is used as a desiccant, as well

as silica gel. Clays are used as inexpensive adsorbents for

some petroleum based applications, mostly they are usedonce then discarded. Fuller’s earth is used to purify oils.

The most important class of inorganics is probably the

zeolites, a subclass of molecular sieves, their specific pores

are located within small crystals. Adsorbents based on

synthetic polymers, like ion exchange or acrylic ester

polymers are commonly used in wastewater treatment.

Most interesting in this connection are carbons. The

carbons have non-polar surfaces that are used to adsorbnon-polar molecules, especially hydrocarbons. They are

manufactured from both organic and inorganic sources,

and can be used to recover solvents, to filter gases or to

purify water. Overall carbons make a broad and im-

portant class of adsorbents (Cussler, 1997).

Conventional methods for treating wastewater con-

taining dyes, aromatic compounds or heavy metals are

coagulation, flocculation, reverse osmosis, nanofiltra-tion and pervaporation (Paul and Ohlrogge, 1998), and

activated carbon adsorption, the latter of which is

combined with membrane processes like nanofiltration

Table 11

Potential product substrate combinations (Fischbach et al., 2000;

Laufenberg et al., 1999)

Substrate Flavour Micro-organism

Apple pomace, spent

malt, spent hops,

carrot pomace

Ethyl butyrate

(pineapple), ethyl

pentanoate (apple),

isoamyl acetate

(banana)

C. fimbriata

Sugar beet pulp

(Asther et al., 1997;

Bonnin et al., 1999;

Lesage-Meessen

et al., 1999)

Vanillin Pycnoporus

cinnabarius, A. niger

Ricinus oil cake

(Feron et al., 2000;

Ferreira et al., 2000)

c-decalactone(peach)

Yarrovia lipolytica

1-Octen-3-ol

(mushroom)

P. pulmonarius

Castor oil cake

(Laufenberg et al.,

2001)

c-decalactone,6-pentyl-a-pyrone(nutty)

M. suaveolens,

T. harzianum

Sunflower seed cake

(Laufenberg et al.,

2001)

c-decalactone T. harzianum

Olive press cake

(Laufenberg et al.,

2001)

c-decalactone,d-decalactone(coconut)

P. ovale, Ceratocys-

tis moniliformis

Soybean coarse meal Pyrazine

(roast flavour)

Bacillus subtilis

Fig. 6. Generation of isoamyl acetate by SSF of spent malt (Fischbach

et al., 2000; Laufenberg et al., 1999).

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 185

Page 20: Vegetal Waste

(Eilers and Melin, 1999; Nicolet and Rott, 1999) orultrafiltration (Lenggenhager and Lyndon, 1997) as

well.

The mentioned processes do not show significant ef-

ficiency or economic advantage. Low cost treatment

methods have therefore been investigated for a long

time. A number of low cost adsorbents have been tried

for wastewater treatment like wool fibres (Balk€oose and

Baltacioglu, 1992), microbial biosorbents (Xie et al.,1996), pillared clays (Baksh et al., 1992), coir pith

untreated (Namasivayam and Kadirvelu, 1996) or acti-

vated (Namasivayam and Kadirvelu, 1997), banana pith

(Namasivayam and Kanchana, 1992), orange peel

(Namasivayam et al., 1996), peanut and walnut shells

(Randall et al., 1974), modified onion skin (Bankar and

Dara, 1982; Kumar and Dara, 1981) corncobs (Haw-

thorne Costa et al., 1995; Tsai et al., 1998), the combi-nation of onion skin with corncobs (Odozi and Emelike,

1985), peanut skin (Randall et al., 1975), palm kernel

husk (Omgbu and Iweanya, 1990), pecan (Ahmenda

et al., 2000a,b) and almond shells (Toles et al., 2000),

sugarcane bagasse (Kumar and Dara, 1982) or func-

tionalised lignin extracted from sugarcane bagasse

(Peternele et al., 1999). Suitable is even black currant

and apple dietary fibre because of its binding capacityfor cadmium and lead (Borycka and Zuchowski, 1998).

Furthermore Namasivayam et al. (1996) mentions peat,

biogas waste slurry, Shukla and Sakhardande (1990)

used cotton and jute fibres, bamboo pulp and saw dust.

The pre-treatment methods for these materials differ,

reaching from chemical extraction of lignin (Peternele

et al., 1999) to adding chemicals and further pyrolysis

(Hussein et al., 1996; Toles et al., 2000; Ahmenda et al.,2000a,b) as included in Table 14, polymerisation

(Bankar and Dara, 1982; Kumar and Dara, 1981;

Randall et al., 1975) or just cutting, drying and grinding

(Namasivayam and Kanchana, 1992; Namasivayam

et al., 1996), see Table 15.

Adsorbents attach atoms, molecules, ions and radi-

cals from their surrounding gaseous or liquid phase onto

their surface. Due to the loose binding forces the layer

thickness on the surface is monomolecular. Adsorptionhappens on the interface, therefore an important crite-

rion for the effectiveness of an adsorbent is its surface

area. Several methods are available to reach as large as

possible surface area like fine grinding, chemical or

biochemical modification, or creating a specific struc-

ture. Hence there is an relation between the natural

properties of vegetable material and the requirements

for high quality adsorbents which could be matchedduring adaptation processing, as visualised in Fig. 7.

Besides a large surface area the optimum adsorbent

has to possess adequate surface chemistry and pore size

distribution to adsorb targeted species. Macropores lead

the component to the micropores where the actual ad-

sorption takes place. Hence the macropores are impor-

tant for diffusion velocity and adsorption kinetics. The

ratio of micro and macropores and total surface areacan be influenced by ZnCl2 addition to the residual

matter. Hussein et al. (1996) described that an addition

of ZnCl2 solution (10 w/w%) to oil palm shells resulted

in enhanced surface area from 950 to 1200 m2 g�1 and

25% micropores, which are important for adsorption

capacity.

Granulated active carbons (GAC) with moderate

surface area (300 m2 g�1), as the case for sugarcanebagasse plus binder corn syrup, exhibit a good pore size

distribution and relatively low surface charge which

explains their good sugar decolourising capacities (Ah-

menda et al., 2000b). Compared to the latter the surface

area of unpyrolysed sugar beet pulp is fairly low, see

Table 12. Physical and chemical activation changes the

Fig. 7. Natural properties of vegetable waste (average) and expected product profile for carbons in wastewater treatment.

Table 12

Surface areas of selected carbon adsorbents

Residual matter Surface area in m2 g�1

Pecan shells (Ahmenda et al., 2000a,b) 1200

Oil palm shell (Hussein et al., 1996) 1200

Sugarcane bagasse and corn syrup

binder (Ahmenda et al., 2000b)

300

Sugar beet pulp (Dronnet et al., 1997) 3

186 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 21: Vegetal Waste

adsorption behaviour of the raw material strongly,Table 14 exhibits a selection of used residues.

Toles et al. (2000) investigated the adsorptive prop-

erties of air-activated almond shells towards several

organics and copper. The almond shell carbon could

remove more than 400% of Cu2þ from the solution

compared to commercial carbon Norite RO3515. The

organic adsorption of almond shell carbon was lower

compared to Filtrasorbe 400, ranging between 84% and92% of the Calgone carbon total adsorption. Con-

vincing as well is the cost estimation: commercial car-

bons are produced for US$ 3.30 per kg, almond shell

carbons for US$ 2.45 per kg. Johns et al. (1998) com-

pared seven commercial GAC with GAC’s made of re-

sidual matter mentioned in Table 14. Both CO2 and

steam activated nutshell carbons consistently removed

more total organics than the commercial GAC’s.The soybean hull based GAC’s showed three or four

times higher copper adsorption compared with all other

commercial or co-product based GACs.

Effective adsorption is as well feasible without phys-

ical or chemical activation. Table 15 is a selection of

vegetable residues used as bioadsorbents for wastewater

treatment so far. The raw material has only been cut,

dried, and ground before the experiments; importantinfluencing parameters arise.

A first series of experiments was done with three

different residues, checking their ability to adsorb

aromatic wastewater components by Laufenberg and

Filipini (2002). Vanillin, representing a substance of

oecotoxic relevance together with benzaldehyde, phenol

and humic acid, has been tested in aqueous solution.

The adsorbing conditions were determined whilechanging the influencing process parameters. As bioad-

sorbents the residues carrot pomace, corncob, and sugar

beet pulp, dried and ground to the particle sizes 125–180

and 710–1500 lm were used.

In a second test series carrot pomace and sugar beet

pulp were inoculated with L. farciminis and fermented

for 20 h. This pre-treatment step was supposed to en-

hance the shelf life of the fresh pomace and to partlydegrade the components. The tests should reveal if there

is any correlation between the targeted metabolism of

lactic acid fermentation and the adsorbent capacity.

Current research in this area is versatile, employing

several residues and experimental conditions, and fo-

cused on different operational modes. In the following

structure and differentiation is given by subdividing the

whole material via the varying process parameters.

4.3.1. Residues, combinations, and synergies

The natural composition of the residual matter deci-sively influences the adsorption capacity. Kumar et al.

(2000) found better removal efficiency for insoluble

straw xanthate (82–99%) than for alkali treated straw

(77–87%) while treating heavy metal solutions. Laufen-berg and Filipini (2002) determined for the adsorption

rate in order of carrot pomace > corncob > sugar beet

pulp. Carrot pomace adsorbed vanillin best at pH 4,

corncob at pH 7 and sugar beet pulp at pH 10.

Kahlert (1999) found that the combination of gelling

agents, using synergetic effects, improves the techno-

logical properties towards a widespread application in

food. These facts may enhance the adsorption capacityand effectiveness too. Odozi and Emelike (1985) com-

bined corncob (lignin and furfural source) and red onion

skin (source of phenolic compounds) and could enhance

the adsorption rate by 20%. The ideal adsorbents should

be rich in lignin and rich in phenols, therefore very

effective residue combinations would be lignin-rich

grape pomace (�45%), olive cake (37%), corncob (17%)

or apple pomace (18%) combined with polyphenolrich green tea waste, mango, orange or grapefruit

peel (Manthey and Grohmann, 1996), see Tables 5 and

6.

A selectivity for special substances may be reached by

combining residues with different binding mechanisms.

Some residues preferably adsorb components by com-

plex formation, others by physical adsorption depending

on the lignin content, as described in Torre et al. (1995).Peternele et al. (1999) describe synergetic effects while

treating wastewater mixtures. The effect was explained

by competition towards the binding sites. The following

selectivity scale was found in adsorption tests for the

divalent metals by Dronnet et al. (1997): Cu2þ PPb2þ � Cd2þ � Zn2þ > Ni2þ > Ca2þ.

In dependency to the application a variety of options

arise. Different residue types may be combined, possiblypre-treated biochemically, or adsorption promoters like

fat and/or fatty acids may be added. Clemente et al.

(1997) suggested olive pomace as a suitable substrate for

adsorption. The natural fat content may even enhance

the efficiency by promoting the monolayer formation.

4.3.2. Particle size

Particle sizes range between 53 and 1500 lm as

exhibited in Table 15. So far only little dependency be-

tween particle size and adsorption rate could be identi-

fied. Ho and McKay (1999) could determine a reducedsorption capacity for colour removal with rising particle

size of sugarcane bagasse pith due to reduced surface

area; as well did Liversidge et al. (1997) with colour

adsorption on linseed cake.

Furthermore the suspension behaviour of particles in

solution is a limiting factor to the process. Contact area

is reduced if the particles sediment too fast. With most

of the investigations the effect was compensated by ag-itation. Laufenberg and Filipini (2002) have used the

polymer Galactomannan (carob flour, molecular weight

310,000 gmol�1), a food thickening agent and stabiliser,

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 187

Page 22: Vegetal Waste

to keep the particles in suspension. Besides the suspen-

sion behaviour the enhanced surface area is an impor-

tant parameter for the adsorption. Table 13 determines

the reduction in surface area per kg carrot pomace in

dependency of the particle sizes. Between the corn

classes 16 and 1700 lm the surface area is reduced by the

factor 100.

Further experiments should determine the effect ofparticle size on adsorption rate. Another possibility to

enhance the contact area could be the fixation of the

bioadsorbents in a packed bed as suggested in Fig. 8.

4.3.3. Adsorbent dosage

At least 2 g residual matter per liter solution was used

in all experiments. An increase of the metal binding with

rising sugar beet pulp concentration was naturally ob-

served by Dronnet et al. (1997). While changing the

adsorbent dosage from 3.64 to 14.55 g l�1 the totally

removed amount of metal was higher, but the slope was

regressive. Nevertheless the concentration of sugar beet

pulp needed for total saturation of all available carboxylfunctions by Cu2þ was not reached. The authors deter-

mined that the complete binding of Cu2þ by carboxy-

lates would occur for an adsorbent dosage of �50 g l�1.

Laufenberg and Filipini (2002) simultaneously varied

adsorption time and adsorbents dosage. Their optimum

adsorbent dosage was determined as 20 g l�1 with a

contact time of 5 min.

4.3.4. Removed component

Most experiments were determined treating dye so-

lutions of different origin or heavy metal solutions,

preferring combinations of copper, cadmium, lead, zinc,

chrome, and nickel. So far only Laufenberg and Filipini

(2002) have removed organics from aqueous solution.

4.3.5. Initial concentration

The initial substance concentration to be treated is

naturally dependent on its solubility in aqueous solu-

tion, it ranges from 5 to 740 mg l�1. For vanillin it couldbe determined that all applied residues adsorbed 10 or

20 mg l�1 vanillin with a similar adsorption rate (Lau-

fenberg and Filipini, 2002). The total vanillin uptake

increased with an increased initial concentration, al-

though the percentage removal decreased. The following

example will clarify:

Table 13

Surface area reduction in dependency of particle size, determined for carrot pomace

Particle size (lm) Mean d (lm) Density (gcm�3) Volume (m3) Surface (m2) Surface (m2 kg�1) Surface (m2 g�1)

0–32 16 1.43 1.71573E)14 3.21699E)09 131.118 0.131

32–63 47.5 1.41 4.48921E)13 2.83529E)08 44.792 0.044

63–90 76.5 1.39 1.87531E)12 7.35415E)08 28.212 0.028

90–125 107.5 1.4 5.20372E)12 1.4522E)07 19.933 0.019

125–180 152.5 1.39 1.48559E)11 2.92247E)07 14.152 0.014

180–250 215 1.39 4.16298E)11 5.8088E)07 10.038 0.010

250–355 302.5 1.39 1.15948E)10 1.1499E)06 7.134 0.007

355–500 427.5 1.37 3.27263E)10 2.29658E)06 5.122 0.005

500–710 605 1.37 9.27587E)10 4.59961E)06 3.619 0.003

710–1000 855 1.35 2.6181E)09 9.18633E)06 2.599 0.002

1000–1400 1200 1.35 7.23823E)09 1.80956E)05 1.851 0.001

1400–2000 1700 1.34 2.05795E)08 3.63168E)05 1.316 0.001

Fig. 8. Design considerations for future packed bed adsorption: (a) vertical adsorber with high volume packed bed (b) ring adsorber and (c)

horizontal thick layer adsorber.

188 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 23: Vegetal Waste

This equilibrium effect is described in several publi-cations (Kumar and Dara, 1981; Bankar and Dara,

1982; Dronnet et al., 1997; Laufenberg and Filipini,

2002).

4.3.6. Agitation type and contact time

Different methods are applied ranging from no agi-

tation (soft mixing at the beginning), over gently mixing

to continuously stirring for 24 h. Very often the particlesare not very stable and tend to leak. Randall et al. (1975)

described the problem while employing peanut skin for

the adsorption of cupric ions; due to the leaking it lost

most of the tannin, too. They suggest a pre-treatment

mixing 1 kg peanut skin with 10 l 0.2 N H2SO4 and 500 g

35% formaldehyde, stirring it for 2 h at 50 �C. Due to

the polymerisation the separated liquid is clear. The

treated peanut skins were more stable, showed no sign

of disintegration even when immersed in water for long

periods. Untreated peanut skins were soft and tended todisintegrate, producing very fine particles which were

difficult to filter.

A contact time of five minutes is sufficient to adsorb

75–85% of the chemical (Laufenberg and Filipini, 2002);

Bankar and Dara (1982) found in equilibrium experi-

ments the maximum sorption for Ca2þ and Mg2þ within

5 min as well.

4.3.7. pH-value

A clear pH dependency was identified, changing withthe chemical adsorbed. Best adsorption results were

achieved for vanillin at an acidic pH, the sequence is

pH 4 > pH 7 > pH 10 (Laufenberg and Filipini, 2002).

Solution Adsorbent

dosage (g)

Bound

chemical

Percentage

removal

10 g

Cu2þ l�11 5.0 g

Cu2þ50

20 g

Cu2þ l�11 7.5 g

Cu2þ37.5

Table 14

Physically and chemically activated carbons made from vegetable residues as a feedstock (selection)

Material/

adsorbents

Particle size Adsorbent

dosage (g l�1)

Removed

component

Initial conc. Agitation type

and time

pH-value Temp.

Almond shells

(Toles et al.,

2000)

10� 20 mesh

size

1 benzene, tolu-

ene, 1,4-di-

oxane, CuCl2,

acetone metha-

nol, acetonitrile

80 mg l�1 Continuously

stirred 24 h

Room temp.

Oil palm shell

(Hussein et al.,

1996)

Characterisation and preparation. ZnCl2 addition of 10 w/w% resulted in higher surface area of 1200 m2 g�1 and 25%

micropores, which are important for adsorption capacity

Sugarcane bag-

asse, pecan

shells, rice hulls

and strawa

(Ahmenda

et al., 2000a,b;

Pendyal et al.,

1999)

12–40 mesh 10 Sugar decolo-

urisation

– Batch test with-

out agitation

Rice straw,

soybean hull,

sugarcane bag-

asse, peanut,

pecan and wal-

nut shells and

seven commer-

cial GACs

(Johns et al.,

1998) (molasses

as binder)

<5 mm, pelle-

tised, activated

with CO2 or

steam, physical

and chemical

activation

100 Benzene,

toluene,

1,4-dioxane,

acetonitrile,

acetone,

methanol

80 mg l�1 500 rpm, 24 h 6–7 23 �C

10 Cu2þ, Cd2þ,

Zn2þ, Ni2þ,

ionic strength

0.03

0.25 mmol of

each metal

250 rpm, 2 h

aAs binders were used sugarcane molasses, sugar beet molasses, corn syrup, coal tar pitch. These binders are necessary to enhance the physical and

chemical properties of the resulting carbon, whilst the adsorption behaviour is still dictated by the residual matter used.

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 189

Page 24: Vegetal Waste

Namasivayam and Kadirvelu (1996) determined an al-kaline pH as a promoter for the adsorption of heavy

metals and alkalis on coir pith, the effect is further de-

scribed for heavy metal adsorption on wool fibres

(Balk€oose and Baltacioglu, 1992), on lignin from sugar-

cane bagasse (Peternele et al., 1999), and the carboni-

sation of oil palm shells (Hussein et al., 1996). For acid

or dye removal the pH should be acidic as described for

orange peel (Namasivayam et al., 1996), or bananapith (Namasivayam and Kanchana, 1992). Dronnet

et al. (1997) realised that positively charged metals are

attracted to negative charges on the adsorbing pomace,

the effect becomes stronger in alkaline solutions.

Torre et al. (1995) investigated the adsorption be-

haviour of grape and olive pomace and lemon peel to-

wards Fe3þ, Fe2þ and Ca2þ. They found with increasing

pH an increase of bound mineral, in addition they de-termined that the quantity of polyvalent cations bound

by dietary fibre materials increases with a higher level of

mineral addition, which is in compliance with other re-

sults. Binding isotherms of Zn2þ increased as the initial

pH of the suspension varied from 3.5 to 7.2. As the pH is

lowered, the overall surface charge on sugar beet pulp

becomes less negative which reduces the attraction of

positively charged metal ions (Dronnet et al., 1997,1998a,b).

4.3.8. Targeted metabolism

Giovannozzi-Sermanni et al. (1995) found with a

targeted metabolism of Lentinus edodes on wheat straw

and corn stalks changing material properties. The mi-

cro-organism, mainly degrading the carbohydrates,

changed the lignin ratio and availability of the raw

material, which resulted in a higher lignin extractability

for alkaline cooking. These observations match with

results obtained by Peternele et al. (1999). Lignin is apotential adsorbents, hence a targeted metabolism of the

vegetable waste prior to the application as a bioadsor-

bents will enhance its adsorption capacity; see in this

connection Table 5 and the differing lignin content of

vegetable residues.

Similar effects are described by Carvalheiro et al.

(1994). Their aim was to enhance protein and lignin

content of tomato pomace to improve its digestibility asa fodder. After SSF for 10 days with a co-culture of T.

reesei and Sporotrichum sp. the cellulose and hemicel-

lulose content was decreased by 67% and 73% re-

spectively, on the other hand the lignin and protein

content rose manifold. A targeted metabolism towards

an enhancement of certain components, i.e., lignin or

cellulose, and thus changed particle properties is feasi-

ble.A targeted metabolism may even govern the ratio

lignin:cellulose (cellulose is used as a chromatography

adsorbent as well) towards the compound to be sepa-

rated. Cellulosic material predominately adsorbs alka-line components as determined by Nawar and Doma

(1989) for the basic dye sandocryl orange. The high af-

finity of the orange dye to cellulosic material like rice

hulls or orange peel is the result of ionic interactions

between the cationic centres on the dyestuff and acidic

sites, mostly carboxylate groups, on the fibres.

The adsorption rate is decisively influenced by the

method of acidification, as aforementioned. Hydro-chloric acid enhances the capacity due to a shift of pH-

value, but the metabolism of selected micro-organisms

additionally influences the particle character (e.g., dif-

ferent configuration of carbohydrates and lignin frac-

tion and/or degradation in total). This targeted

metabolism is superior. The fermented samples did not

need any pH adjustment, were stable in shape and initial

pH and tended to adsorb more substance than the HCl-adjusted samples (Laufenberg and Filipini, 2002).

4.3.9. Surface area

Ahmenda et al. (2000a,b) described a low surface area

for their soft materials sugarcane bagasse, rice hulls andstraw independently of chemical or physical activation.

They found that the total surface area does not correlate

with adsorption efficiency and suggested pore size dis-

tribution as well as surface charges play an important

role too. It seems that the low surface area of untreated

residues does not have the major effect on the adsorp-

tion process (Tables 12 and 13), other parameters may

be stronger as expected, see Fig. 7. Removal rates inTable 15 up to 90% are convincing.

4.3.10. Binding mechanisms

Kumar et al. (2000) observed that basic groups of

straw and straw xanthate interact with Cr3þ via an ionexchange route. For each Cr3þ exchanged, one equiva-

lent of Naþ is released into the solution, hence the so-

lution became alkaline.

Laufenberg and Filipini (2002) noted a clear tendency

of the pH-adjusted carrot pomace and sugar beet pulp

to return to its initial pH after a certain time due to the

ion exchange mechanism. Kumar and Dara (1981) tes-

ted the binding capacity of polymerised onion skinstowards several heavy metals in aqueous solutions.

During their equilibrium experiments they determined

that in all studied cases the final pH of the metal-

adsorbent-solution was always less than the initial pH.

This effect indicates that, as the metal ions are bound on

the substrate, hydrogen ions are released into the solu-

tion. The authors concluded that the onion skin sub-

strate probably acts as an acid-form ion exchanger. Thetheory was confirmed for other materials like sugarcane

bagasse (Kumar and Dara, 1982; Dronnet et al., 1997),

onion skin (Bankar and Dara, 1982), onion skin and

190 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 25: Vegetal Waste

Table 15

Vegetable residues as bioadsorbents: influencing process parameters

Material/adsorbents Particle size

(lm)

Adsor-

bent

dosage

(g l�1)

Removed component Initial concentration Agitation type/time pH-value Temp. (�C) Ionic strength

Apple/black currant

pomace (Borycka and

Zuchowski, 1998)

6 180 and

710–1500

10 and

20

Cd, Pb, Ca, low 30–40% – – – – –

Banana pith (Namasiva-

yam and Kanchana, 1992)a53–1000 0.5–6 Textile dyes, up to 80% 20–100 mg l�1 140 rpm/20–200 min. 2"–11# 30� 2 –

Carrot pomace and sugar

beet pulpb (Laufenberg and

Filipini, 2002)

125–180 and

710–1500

10 and

20

Vanillin, humic acid 10 and 20 mg l�1 No agitation/5, 10,

20 min, and 1, 8, 24

h

4", 7, 10# 23� 2 –

Coconut coir pith

(Kadirvelu et al., 2001)

53–1000 2.5, 5, 6,

9

Hg2þ, Pb2þ, Cd2þ, Cu2þ,

Ni2þ 73–100%

126, 709, 996 mg l Batch mode 2#–10" – –

Corncobs (Hawthorne

Costa et al., 1995)

– 30 Cu2þ 6� 103; 0:5� 104 mole l�1 Continuous/15 min. 6 35 0.1, 0.5 and 0.9

mol l�1

Corncobs, wood chips,

wheat straw (Nigam et al.,

2000)

3, 0.3, and 0.2

mm3

100 Several red, blue and

black dyes; 70–75% re-

moval

200–500 mg l�1 Soaking for 48 h – 20, 30 or 48 –

Corncobs mixed with onion

skin (Odozi and Emelike,

1985)c ;d ;e

<200 10 Ni, Mg, Zn, Pb, Cd, Ca,

Hg, Mn-cations

142–740 mg l�1 Continuous/24 h "6 and

higher,

lower #

Room temp. –

Linseed cake and peat

(Liversidge et al., 1997)

180–1000 2 Basic blue 41–95% re-

moval, acid blue 148, re-

active red 184

50–2000 mg l�1 120 rpm/90 min. 30"þ50#strange!

Onion skin, sugarcane

bagasse, bark (Kumar and

Dara, 1981)f ;c

– 10 Hg, Cd, Ni, Zn, Cr, Pb 45–100 mg l�1 – 2–11 – –

Onion skins (Bankar and

Dara, 1982)c ;gPowdered 40 Ca2þ, Mg2þ 0.4–20� 103 mg l�1 Ca2þ,

0.2–1200 mg l�1 Mg2þGently agitated/10

min.

4–10", less#

30, 50, 100 –

Orange peel (Namasivayam

et al., 1996)

75–500 2–10 Dyes, 73–92% 10–60 mg l�1 140 rpm/20–90 min 3"–12# 29� 2 –

Palm kernel husk (Omgbu

and Iweanya, 1990)c>500 2 Pb2þ 60–80%, Zn2þ 13–

24%

5–25 mg l�1 – – – –

Peanut skins (Randall

et al., 1975)c<1000 10 Cu2þ 10 mg l�1 Gently agitated/30

min

6 or higher Room temp. –

Rice hulls, peat and acti-

vated carbon (Nawar and

Doma, 1989)c

160, 300, and

1200

10 Sandocryl orange 98%

and lanasyn black 78%

50 mg l�1 15"–120 min Black 3–6,

orange 2–

11

Room temp. –

Sugar beet pulpd ;f (Dron-

net et al., 1997, 1998a,b)

200–500 1.82,

7.27,

14.55

Ca2þ, Pb2þ Cd2þ, Zn2þ,

Ni2þ, Ca2þ, 72% removal,

10 min

0.01 M solution Constantly stirred/2

h

3.5–7" 25� 1 –

Sugarcane bagasse

(Peternele et al., 1999)d– 5 Cd2þ, Pb2þ 1–6 mmol dm�3 Shaking/8 h "5 or 6" 30, 40, "50 "0.5 and 1.0

mol dm�3

G.Laufen

berg

etal./Bioreso

urce

Tech

nology87(2003)167–198

191

Page 26: Vegetal Waste

corncobs (Odozi and Emelike, 1985), peanut skins

(Randall et al., 1975), palm kernel husks (Omgbu and

Iweanya, 1990) or pure corncobs (Hawthorne Costa

et al., 1995). Since the latter residue is mainly lignin and

cellulose based several residual matters, e.g., olive cake

or white wine pomace, could be taken into account for

future adsorption of dyes, heavy metals and chemicals,

see Table 5.Certain mechanisms for the uptake of components

from solutions are discussed according to the type of

substrate used (Dronnet et al., 1997). An overview of

binding mechanisms is given in Table 16. Some simple

chemical or physical modifications may improve the

adsorbent behaviour of these materials several times.

Modification reactions include crosslinking and/or

functionalisation to enhance the adsorbent stability and/or capacity (Peternele et al., 1999).

4.3.11. Packed bed design

Adsorption is much more effective in a packed bedthan in a stirred tank, which is an equivalent to count-

ercurrent flow in extraction. A packed bed will permit

faster mass transfer and higher conversion. Assumed is

that a large volume of solution is to be fed through a

small bed of adsorbing solid. The bed is completely

uniformly packed and the flow moving evenly, without

dispersion and independent of the bed’s radius. Hence in

the packed bed the concentration in the solid is inequilibrium with the high feed concentration. In stirred

tank loaded solid reaches equilibrium with depleted so-

lution which is less than with the feed solution. There-

fore yields are much less effective (Cussler, 1997).

The results of several investigations match with the

described relations. Namasivayam et al. (1996), Na-

masivayam and Kanchana (1992) and Peternele et al.

(1999) realised that an increase in the initial substanceconcentration increased the amount of substance ad-

sorbed. It was clearly shown that the removal of dye or

metal is dependent on its initial concentration in solu-Table

15(continued)

Material/adsorbents

Particle

size

(lm)

Adsor-

bent

dosage

(gl�

1)

Rem

oved

component

Initialconcentration

Agitationtype/time

pH-value

Tem

p.(�C)

Ionic

strength

Sugarcanebagassepith

(HoandMcK

ay,1999)

150"–1000#

0.251.5

Basicred22andacidred

114

50–300mgl�

1–

–20–80"

Wheatstraw

andinsoluble

straw

xanthate

(Kumar

etal.,2000)

1000

20

Cr3

þ,Cr6

þCr,Pb,Cu,

Ni,Fe,

Mn,Zn

37.3

mgl�

1Cr64mgl�

1others

�0.5

mgl�

1

Continuous/15min

3.6

25�1

Woolfibres(Balk€ oose

and

Baltacioglu,1992)

17onaverage

15

Ni,Cu,Zn,Cd,Hg,Pb

70%

50–200mgl�

1Constantly/upto

60

min

–25or50,no

effect

(")increasedadsorption,(#)decreasedadsorption,(–)nodata

available.

aWithincreasingagitationtimetherewasadecrease

indiffusionlayer

thickness.

bTargeted

metabolism

hasledto

differentpH

values

andmaterialproperties.

cDid

additionalcolumntests.

dSelectivityscale,synergisticeffects.

e20%

higher

adsorptionrate

onaveragedueto

columntest

andcombinationofresidues.

fSelectivityfortheionsare

dependingonthetypeofpomace

tooandabsolute

adsorptionrate

increasedwithhigher

initialconcentration.

gPreferred

adsorptionofCa2þ.

Table 16

Physicochemical mechanisms for the uptake of components from so-

lutions

Residue or main component Mechanism

Sugar beet pulp; responsible are the

galacturonosyl units of the pectic chains

(Dronnet et al., 1997, 1998a)

Ion exchange

Soybean hulls, peanut shells, sugar cane

bagasse, rice straw (Johns et al., 1998)

Ion exchange, chelation,

and coordination, but

without modification also

surface precipitation

Corncobs (Hawthorne Costa et al.,

1995): carboxylate groups

Ion exchange

Straw and straw xanthane (Kumar

et al., 2000)

Ion exchange

192 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 27: Vegetal Waste

tion due to the change in equilibrium limit. This is the

aforesaid disadvantage of the stirred tank. It could be

transferred into an advantage if the adsorption would

take place in a packed bed. Possible design consider-

ations are given in Fig. 8. Similarities are described by

Balk€oose and Baltacioglu (1992), they suggest further

experiments with controlled flow rates and tightly

packed wool beds. Kumar and Dara (1982) achievedhigher adsorption results in a column for all tested

heavy metals, also did Bankar and Dara (1982) and

Randall et al. (1975).

4.3.12. Post-treatment

Nigam et al. (2000) removed several textile dyes fromeffluents using the residues wheat straw, wood chips and

corncob shreds. The adsorption rate was rather good,

up to 75% of the dyes could be removed. The authors

additionally investigated the suitability of the dye-

adsorbed residues for SSF by the white-rot fungi

Phanerochaete chrysosporium and Coriolus versicolor,

both possessing dye degradation capabilities. It could be

determined that both dye adsorbed residues wheat strawand corncob shreds were heavily colonised and hence

are suitable substrates for fungal colonisation. Visual

substrate decolourisation occurred; which has to be

precisely determined in future experiments. The fer-

mented residue is useful as a soil conditioner. Other

groups have used Pleurotus pulmonarius for the degra-

dation of antrazine (Masaphy et al., 1996).

Depending on the recycling method for the spentadsorbents an equal ratio between adsorption and de-

sorption becomes an important goal. The high adsorp-

tion rate is the only point of interest if the laden

adsorbents is afterwards metabolised by micro-organ-

isms. A regeneration/desorption has to be taken into

account, if the substances should be recycled, several

methods are described (Hamer and P€uuschner, 1997;

Urano and Tachikawa, 1992; Urano et al., 1992).

4.3.13. Future considerations

Depending on the origin the residues adsorb more or

less water. Oil press cakes, like olive or sunflower cake,

exhibit little water binding capacity, beverage residues

like carrot or grape pomace swell considerably in water.

Hydration properties can be reduced by establishing

cross-links between the cell wall polysaccharides using

the pre-treatment chemicals formaldehyde (Kumar

and Dara, 1982; Randall et al., 1975; Dronnet et al.,

1998a,b), epichlorohydrin, divinylsulfone, glutaric di-

aldehyde, or citric acid. The saponification doubledthe cation-exchange capacity, and epichlorohydrin was

most effective improving the binding properties of the

investigated beet pulp per unit of hydrated volume, i.e.,

decreased its hydration properties and increased metal

binding capacities (Dronnet et al., 1998a,b).

Laufenberg and Filipini (2002) found that their bio-

adsorbents carrot pomace and sugar beet pulp exhibit

some properties which are difficult to handle, these arein particular: no stable size, the particles are brittle, the

colour leaking distorts the results, and the phase sepa-

ration is difficult. Corrective actions in future experi-

ments should include

• mechanical pre-treatment to enlarge surface area and/

or stabilize the suspension,

• chemical pre-treatment to prevent colour leaking,• packed bed technology to enhance effectiveness to-

wards the equilibrium limit, enlarge contact area

and to simplify phase separation, desorption, and re-

cycling,

• SSF to change particle composition and naturally in-

fluence pH-value,

• extrusion to add promoters, concentrate existing pro-

moters, remove disturbing components, combine twomaterials with differing properties, coat or line com-

ponents, and influence the suspension behaviour,

• adding fat containing residues like olive cake to re-

duce the brittleness.

5. Conclusions and outlook

This clean production concept shows a good utilisa-

tion potential for solid vegetable waste. It could achieve

a reduction of investment and raw material costs and

Table 17

Adsorption parameters and economic evaluation of three adsorbents (Nawar and Doma, 1989)

Compound used Adsorbents material,

particle size 0.3–0.4 mm

Adsorbent dosage (g l�1) Comparative cost

per kg adsorbent

Comparative cost

to remove kg dye

Comparative cost to

remove kg dye in (%)

Sandocryl orange Peat 1.8 0.04 1.46 0.53

Rice hulls 16.3 0.01 3.3 1.52

Activated carbon 13.6 1 277 –

Lanasyn black Peat 72 0.04 58 1.4

Rice hulls 77.7 0.01 15.8 0.38

Activated carbon 204 1 4163

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 193

Page 28: Vegetal Waste

can contribute to a waste minimised food production.Especially the development of bioadsorbents is a prom-

ising area to add value to vegetable residues. They will

appear as a cheap and environmentally safe alternative

to commercial ion-exchange resins.

Nawar and Doma (1989) have made economical

considerations for three bioadsorbents at equilibrium

under similar experimental conditions in 1989. They

used peat, rice hulls and activated carbon for stirredtank and fixed bed experiments to remove dyes from

wastewaters. The costs of removal of 1 kg of each of the

studied dyes via different adsorbents showed that for

sandocryl orange the costs of peat are 0.53% and of rice

hulls 1.52% of the costs of activated carbon. For lanosyl

black removal the values are 1.4% and 0.38%, respec-

tively, see Table 17.

The cheapness of rice hulls in particular and vegeta-ble residues in general means that regeneration is a

further goal in clean production but under economic

considerations not absolutely necessary.

Acknowledgements

Special thanks to Conny Schnitter, MEng, who spentfour weeks in Lappeenranta/Finland doing the adsorp-

tion experiments and setting up the analysis.

References

Abu-Qudais, M., 1996. Fluidized-bed combustion for energy produc-

tion from olive cake. Energy 21 (3), 173–178.

Ahmenda, M., Marshall, W.E., Rao, R.M., 2000a. Production of

granular activated carbons from select agricultural by-products

and evaluation of their physical, chemical and adsorption proper-

ties. Bioresource Technology 71, 113–123.

Ahmenda, M., Marshall, W.E., Rao, R.M., 2000b. Surface properties

of granular activated carbons from agricultural by-products and

their effects on raw sugar decolorization. Bioresource Technology

71, 103–112.

Almosnino, A.M., Belin, J.M., 1991. Apple pomace: an enzyme system

for producing aroma compounds from polyunsaturated fatty acids.

Biotechnology Letters 13 (12), 893–898.

Al-Wandawi, H. et al., 1985. Tomato processing wastes as essential

raw material source. Journal of Agriculture and Food Chemistry

33, 804–807.

Anon., 1999. Gesunde Rott€oone. Lebensmitteltechnik 7–8, 38.

Arogba, S.S., 1999. The performance of processed mango (Mangifera

indica) kernel flour in a model food system. Bioresource Techno-

logy 70, 277–281.

Asther, M. et al., 1997. Fungal biotransformation of European

agricultural by-products to natural vanillin: a two-step process.

Food Ingredients Porte de Versailles, Paris, France, 12–14

November 1996, pp. 123–125.

Attri, B.L., Maini, S.B., 1996. Pectin from galgal (Citrus pseudolimon

tan.) peel. Bioresource Technology 55 (1), 89–91.

Baksh, M.S., Kikkinides, E.S., Yang, R.T., 1992. Characterization by

physisorption of a new class of microporous adsorbens: Pillared

clays. Industrial Engineering and Chemical Research 31 (9), 2181–

2189.

Balk€oose, D., Baltacioglu, H., 1992. Adsorption of heavy metal cations

from aqueous solutions by wool fibers. Journal of Chemical

Technology and Biotechnology 54, 393–397.

Bankar, D.B., Dara, S.S., 1982. Binding of calcium and magnesium by

modified onion skins. Journal of Applied Polymer Science 27,

1727–1733.

Bonnin, E. et al., 1999. Enhanced bioconversion of vanillic acid into

vanillin by the use of ‘natural’ callobiose. Journal of the Science of

Food and Agriculture 79, 484–486.

Borycka, B., 1996. Fruit pomace in new dietary fiber compositions.

Przemysl-Fermentacyjny-i-Owocowo-Warzywny (Poland) 40 (12),

37–39.

Borycka, B., Zuchowski, J., 1998. Metal sorption capacity of fibre

preparations from fruit pomace. Polish-Journal-of-Food-and-Nu-

trition-Sciences 7 (48), 67–76.

Bramorski, A., Soccol, C.R., Christen, P., Revah, S., 1998. Fruity

aroma production by Ceratocystis fimbriata in solid cultures

from agro-industrial wastes. Revista de Microbiologia 28 (3),

208–212.

Brose, D.J., 1993. Novel process technology for utilisation of fruit and

vegetable waste. SBIR Phase I project USDA ICSRS, Washington,

DC.

Broughton, N.W., Dalton, C.C., Jones, G.C., Williams, E.L., 1995a.

Adding value to sugar beet pulp. Hoehere Erloese aus Zuckerrue-

benschnitzeln. Zuckerindustrie 120 (5), 411–416.

Broughton, N.W., Dalton, C.C., Jones, G.C., Williams, E.L., 1995b.

Adding value to sugar beet pulp. International Sugar Journal 97

(1154), 57–60, 93–95.

Bundschuh, E., Baumann, G., Gierschner, K., 1988. Untersuchungen

zur CO2-Hochdruckextraktion von Aromastoffen aus Reststoffen

der Apfelverarbeitung. Deutsche Lebensmittelrundschau 84, 205–

210.

Bundschuh, E. et al., 1986. Gewinnung von nat€uurlichen Aromen aus

Reststoffen der Lebensmittelproduktion mit Hilfe der CO2-Ho-

chdruckextraktion. Lebensmittelwissenschaft und Technologie 19,

493–496.

Carson, K.J., Collins, J.L., Penfield, M.P., 1994. Unrefined, dried

apple pomace as a potential food ingredient. Journal of Food

Science 59 (6), 1213–1215.

Carvalheiro, F., Roseiro, J.C., Collaco, M.T.A., 1994. Biological

conversion of tomato pomace by pure and mixed fungal cultures.

Process biochemistry 29 (7), 601–605.

Chkhikvishvili, I.D., Gogiya, N.N., 1995. Flavonoids of mandarin

fruit wastes and their fungistatic effect on the fungus Phoma

tracheiphila. Applied Biochemistry and Microbiology 31 (3), 292–

296.

Christen, P., Bramorski, A., Revah, S., Soccol, C.R., 2000. Charac-

terization of volatile compounds produced by Rhizopus strains

grown on agro-industrial solid wastes. Bioresource Technology 71,

211–215.

Christen, P., Meza, J.C., Revah, S., 1997. Fruity aroma production in

solid state fermentation by Ceratocystis fimbriata: influence of the

substrate type and the presence of precursors. Mycological

Research 101 (8), 911–919.

Christen, P., Villegas, E., Revah, S., 1994. Growth and Aroma

production by Ceratocystis fimbriata in various fermentation

media. Biotechnology letters 16 (11), 1183–1188.

Chu, D.C., Juneja, L.R., 1997. General chemical composition of green

tea and its infusion. In: Yamamoto, T. et al. (Eds.), Chemistry and

applications of Green tea. CRC Press, New York (Chapter 2).

Clarke, S., 1995. Eat bagasse. Sugar Journal 58, 12.

Clemente, A., Sanchez-Vioque, R., Vioque, J., Bautista, J., Millan, F.,

1997. Chemical composition of extracted dried olive pomaces

containing two and three phases. Food-Biotechnology 11 (3), 273–

291.

194 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 29: Vegetal Waste

Cordova, J. et al., 1998. Lipase production by solid state fermentation

of olive cake and sugar cane bagasse. Journal of Molecular

Catalysis B: Enzymatic 5 (1–4), 75–78.

Couteau, D., Mathaly, P., 1998. Fixed-bed purification of ferulic acid

from sugar beet pulp using activated carbon: optimization studies.

Bioresource Technology 60, 17–25.

Cussler, E.L., 1997. Diffusion, second ed. Cambridge University Press,

New York.

Dexter, J.E., Wood, P.J., 1996. Recent applications of debranning of

wheat before milling. Trends in Food Science and Technology 7

(2), 35–41.

Dronnet, V.M., Axelos, M.A.V., Renard, C.M., Thibault, J.F., 1997.

Binding of divalent metal cations by sugar-beet pulp. Carbohydrate

Polymers 34, 73–82.

Dronnet, V.M., Axelos, M.A.V., Renard, C.M., Thibault, J.F., 1998a.

Improvement of the binding capacity of metal cations by sugar-

beet pulp. 1. Impact of cross-linking treatments on composition,

hydration and binding properties. Carbohydrate polymers 35, 29–

37.

Dronnet, V.M., Axelos, M.A.V., Renard, C.M., Thibault,

J.F., 1998b. Improvement of the binding capacity of metal cations

by sugar-beet pulp. 2. Binding of divalent metal cations

by modified sugar-beet pulp. Carbohydrate polymers 35, 239–

247.

Duerre, P., 1998. New insights and novel developments in clostridial

acetone/butanol/isopropanol fermentation. Applied Microbiology

and Biotechnology 49, 639–648.

Eilers, L., Melin, T., 1999. Nanofiltration kombiniert mit Adsorption

an Pulverkohle f€uur die Abwasserreinigung. In: 7th Aachener

Membrankolloquium 9–13.03.1999 (D), pp. 343–346.

El-Nawawi, S.A., Heikal, Y.A., 1996. Production of pectin pomace

and recovery of leach liquids from orange peel. Journal of Food

Engineering 28 (3/4), 341–347.

Feil, H., 1995. Biodegradable plastics from vegetable raw materials.

Agro-Food-Industry-Hi-Tech. 6 (4), 25–32.

Feron, G., Bonnarme, P., Durand, A., 1996. Prospects for the

microbial production of food flavours. Trends in Food Science

and Technology 7, 285–293.

Feron, G., Wang, X.-D., Viel, C., Perrin, C., Mauvais, G., Cachon, R.,

Divi�ees, C., 2000. Influence of a reduction agent on the bioconver-

sion of ricinoleic acid to y-decalactone by the yeast Sporidiobolus

ruinenii: cellular and enzymatic approaches. Biotechnology 2000:

Book of Abstracts 3 Poster VI, 146, p. 604.

Ferreira, P., Diez, N., Soilveri, J., Copa-Patino, J.L., 2000. Screening

of different Streptomycetes for the ability to produce ferulic acid

from sugar beet pulp. Biotechnology 2000: Book of Abstracts 3

Poster V. 84, p. 276.

Filipini, M., Hogg, T., 1997. Upgrading of vegetable wastes and

applications in the food industry. In: 11 Forum for Ap-

plied Biotechnology. Gent (Belgium). 25–26 September 1997.

Mededelingen-Faculteit-Landbouwkundige-en-Toegepaste-Biolog-

ische-Wetenschappen-Universiteit-Gent (Belgium). 62(4a) pp.

1329–1331.

Fischbach, R., Laufenberg, G., Kunz, B., 2000. Generation of

natural flavours by solid-state fermentation of food industry

by-products. In: Proceedings of Biotechnology 2000, 03–

08.09.00, Berlin, Frankfurt/Main: Dechema e.V., vol. 4. pp. 266–

268.

Giovannozzi-Sermanni, G. et al., 1995. Paper biopulping of agricul-

tural wastes by Lentinus edodes (Chapter 22). In: Sadler, J.N.,

Penner, M. (Eds.), Degradation of insoluble Carbohydrates. ACS

Press, Washington, DC, pp. 339–351.

Gomes, T., Caponio, F., 1997. Evaluation of the state of oxidation of

crude olive-pomace oils. Influence of olive-pomace drying and oil

extraction with solvent. Journal of Agriculture and Food Chem-

istry 45 (4), 1381–1384.

Grigelmo-Miguel, N., Martin-Belloso, O., 1999. Influence of fruit

dietary fibre addition on physical and sensorial properties of

strawberry jams. Journal of Food Engineering 41, 13–21.

Grohmann, K., Bothast, R.J., 1994. Pectin-rich residues generated by

processing of citrus fruits, apples, and sugar beets: enzymatic

hydrolysis and biological conversion to value-added products.

ACS-symp-ser, vol. 566. American Chemical Society, Washington,

DC, pp. 372–390.

Gupta, R., Chauhau, T.R., Lall, D., 1993. Nutritional potential of

vegetable waste products for ruminants. Bioresource Technology

44 (3), 263–265.

Haddadin, M.S., Abdulrahim, S.M., Al-Kawaldeh, G.Y., Robinson,

R.K., 1999. Solid state fermentation of waste pomace from olive

processing. Journal of Chemical Technology and Biotechnology

74, 613–618.

Hamer, A., P€uuschner, H., 1997. Untersuchungen zur L€oosungsmit-

telr€uuckgewinnung aus der w€aassrigen Phase durch Adsorption und

Desorption mit Mikrowellenenergie. Chemie Ingenieur Technik 69,

480–483.

Haque, K.S., Tareque, A.M., Zaman, M.A., 1997. Chemical analysis

of nutritive values of fruit wastes. Bangladesh Veterinary Journal

31 (1–2), 54–56.

Hartman, H., 1996. Scent and taste. Perfumer and Flavorist 21 (2), 21–

24.

Hausmanns, S., Laufenberg, G., Lipnitzki, F., Field, R., 1999.

Prospects and performance of hydrophobic pervaporation in the

concept of clean production. In: 2nd Asia-Pacific Cleaner Pro-

duction Roundtable and Trade Expo, Brisbane April 21–24,

1999.

Hawthorne Costa, E.T. et al., 1995. Removal of cupric ions from

aqueous solutions by contact with corncobs. Separation Science

and Technology 30 (12), 2593–2602.

Henn, T., 1998. Untersuchungen zur Entwicklung und Bewertung

funktioneller Lebensmittelzutaten aus Reststoffen am Beispiel von

M€oohrentrestern und ihrer Anwendung in Getr€aanken (Thesis Bonn/

D 1998) Cuvillier Verlag G€oottingen.

Henn, T., Kunz, B., 1996. Zum Wegwerfen zu schade. ZFL 47 (1/2),

21–23.

Higareda, R.A. et al., 1995. Commercial pectin concentrate from

hawthorn pulp. Revista Chapingo, Serie Horticultura 1 (4), 155–

157.

Ho, Y.S., McKay, G., 1999. A kinetic study of dye sorption by

biosorbent waste product pith. Resources, Conservation and

Recycling 25, 171–193.

Huber, W., Fo�aa, D., 1999. Eine reine Geschmacksfrage. Lebensmit-

teltechnik 9, 52–54.

Hussein, M.Z., Tarmizi, R.S.H., Zainal, Z., Ibrahim, R., 1996.

Preparation and characterization of active carbons from oil palm

shells. Carbon 34 (11), 1447–1454.

Inglett, G.E., 1998. New cereal products with health benefits. Food

Ingredients Europe, Conference Proceedings, 17–19.

Johns, M.M., Marshall, W.E., Toles, C.A., 1998. Agricultural by-

products as granular activated carbons for adsorbing dissolved

metals and organics. Journal of Chemical Technology and

Biotechnology 71, 131–140.

Joshi, V.K., Sandhu, D.K., 1996. Preparation and evaluation of an

animal feed byproduct produced by solid-state fermentation of

apple pomace. Bioresource Technology 56 (2/3), 251–255.

Kadirvelu, K., Thamaraiselvi, K., Namasivayam, C., 2001. Removal

of heavy metals from industrial wastewaters by adsorption onto

activated carbon prepared from an agricultural solid waste.

Bioresource Technology 76, 63–65.

Kahlert, S., 1999. Stabile IQF-Produkte. Lebensmitteltechnik 4, 68–69.

K€ooksel, H., €OOzboy, €OO., 1999. Effects of sugar beet fiber on cookie

quality Einfluß von Zuckerr€uu benfaserstoffen auf die Qualit€aat von

Cookie-Keksen. Zuckerindustrie 124 (7), 542–544.

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 195

Page 30: Vegetal Waste

Kriener, M., 1999. Naturnaher Pflanzenbau-€OOkoweine sind nicht nur

gesund, sie schmecken auch besser. K€oolner Stadtanzeiger 237 (9/

10), 28.

Mukherjee, K., Sen, B., 1998. Biological control of Fusarium wilt of

muskmelon by formulations of Aspergillus niger. Israel Journal of

Plant Sciences 46 (1), 67–72.

Kruszewska, I., Thorpe, B., 1995. What is clean production? HTML

version of a Greenpeace Briefing, http://www.rec.org/Poland/wpa/

cpb.htm.

Kumar, A., Rao, N.N., Kaul, S.N., 2000. Alkali-treated straw and

insoluble straw xanthate as low cost adsorbents for heavy metal

removal-preparation, characterization and application. Biore-

source Technology 71, 133–142.

Kumar, P., Dara, S.S., 1981. Binding heavy metal ions with polymer-

ized onion skin. Journal of Polymer Science: Polymer Chemistry

edition 19, 397–402.

Kumar, P., Dara, S.S., 1982. Utilisation of agricultural wastes for

decontaminating industrial/domestic wastewaters from toxic met-

als. Agricultural Wastes 4, 213–223.

Kunz, B., 1999. €AApfel f€uur Bananenduft. Der Spiegel 48, 273.

Kuper-Theodoritis, S., 1996. Emissionen der Lebensmittelindust-

rie, ihre Vermeidung, Verwertung und Entsorgung. In: Heiss,

R. (Ed.), Lebensmitteltechnologie. Springer, New York (Chapter

47).

Larrauri, J.A. et al., 1999. New approaches in the preparation of high

dietary fibre powders from food by-products. Trends in Food

Science and Technology 10 (1), 3–8.

Laufenberg, G., Rosato, P., Kunz, B., 2001. Conversion of vegetable

waste into value added products: oil press cake as an exclusive

substrate for microbial d-decalactone production. In: Lecture at

Lipids, Fats, and Oils: Reality and public perception. 24th world

congress and exhibition of the ISF, 16–20.09.01. BerlinD, AOCS

press, pp.10ff (ISBN: 1-893997-16-x).

Laufenberg, G., Filipini, M., 2002. Adding value to vegetable waste:

particle characterization and adsorption properties of food indus-

try residues. Environ. Prog. (submitted).

Laufenberg, G., Gr€uuß, O., Kunz, B., 1996. Neue Konzepte der

Reststoffverwertung in der Lebensmittelindustrie––Chancen f€uur dieKartoffelst€aarkeindustrie. New concepts for the utilisation of

residual products from food industry––Prospects for the potato

starch industry. Starch-St€aarke 48, 315–321.

Laufenberg, G., Hausmanns, S., Kunz, B., Nystroem, M., 1999. Green

productivity concept for the utilisation of residual products from

food industry––trends and performance. In: Lecture at the 2nd

Asia-Pacific Cleaner Production Roundtable and Trade Expo,

Brisbane 21–24 April, 1999.

Laufenberg, G.H., Cussler, E.L., 1999. Recovery of bioflavours by

hollow fibre membrane contactors. In: Euromembrane 99, 19–22

September, 1999. Leuven, Belgium, pp. 317–318.

Lenggenhager, T., Lyndon, R., 1997. Profit-generating benefits of

ultrafiltration and adsorber technology. Fruit Processing 7, 250–

256.

Lesage-Meessen, L. et al., 1999. Fungal transformation of ferulic acid

from sugar beet pulp to natural vanillin. Journal of the Science of

Food and Agriculture 79, 487–490.

Liversidge, R.M., Lloyd, G.J., Wase, D.A.J., Forster, C.F., 1997.

Removal of basic blue 41 dye from aqueous solution by linseed

cake. Process Biochemistry 32 (6), 473–477.

Lu, Y., Foo, L.Y., 1997. Identification and quantification of ma-

jor polyphenols in apple pomace. Food Chemistry 59 (2), 187–

194.

Lucarini, M. et al., 1999. Endogenous markets for organic versus

conventional plant products. In: H€aagg, M. et al. (Eds.) Agri-Food

Quality II, Quality management of Fruits and Vegetables. Confer-

ence proceedings of a congress held on 22–25.04.1998 in Turku,

Finland. Royal society of Chemistry, Cambridge, UK, pp. 306–

310.

Lucas, J. et al., 1997. Fermentative utilization of fruit and vegetable

pomace (biowaste) for the production of novel types of products–

results of an air project. In: Proceedings of the eleventh forum

for applied biotechnology, Gent, Belgium, 25–26 September,

1997, Part II. Mededelingen-Faculteit-Landbouwkundige-en-Toe-

gepaste-Biologische-Wetenschappen, Universiteit-Gent. 62(4b),

1865–1867.

Majid, A., Haroon, S., Joarder, G.K., 1995. High protein feed from

vegetable waste. Bangladesh Journal of Scientific and Industrial

Research 30 (2–3), 1–11.

Manthey, J.A., Grohmann, K., 1996. Concentrations of Hesperi-

din and other orange peel flavonoids in citrus processing

byproducts. Journal of Agriculture and Food Chemistry 44, 811–

814.

M�aari�aassyov�aa, M. et al., 1999a. Red beet as source of pigments. In:

H€aagg, M. et al. (Eds.) Agri-Food Quality II, Quality management

of Fruits and Vegetables. Conference Proceedings of a Congress

held on 22–25.04.1998 in Turku, Finland. Royal society of

Chemistry, Cambridge, UK, pp. 306–310.

M�aari�aassyov�aa, M., �SSilh�aar, S., Kov�aac, M., 1999b. New sources for

anthocyanins. In: H€aagg, M. et al. (Eds.) Agri-Food Quality II,

Quality management of Fruits and Vegetables. Conference Pro-

ceedings of a Congress held on 22–25.04.1998 in Turku, Finland.

Royal society of Chemistry, Cambridge, UK, pp. 311–313.

Martin, A.M. (Ed.), 1998. Bioconversion of waste materials to

industrial products, second ed. Blackie Academic & Professional,

London.

Martin-Cabrejas, M.A., Esteban, R.M., Lopez-Andreu, F.J., Wal-

dron, K., Selvendran, R.R., 1995. Dietary fiber content of pear and

kiwi pomaces. Journal of Agriculture and Food chemistry 43 (3),

662–666.

Martin-Carron, N., Garcia-Alonso, A., Goni, I., Saura-Calixto, F.,

1997. Nutritional and physiological properties of grape pomace as

a potential food ingredient. American Journal of Enology and

Viticulture 48 (3), 328–332.

Masaphy, S., Levanon, D., Henis, Y., 1996. Degradation of antrazine

by the Lignocelluloytic Fungus Pleurotus pulmonarius during solid-

state fermentation. Bioresource Technology 56, 207–214.

Masoodi, F.A., Chauhan, G.S., 1998. Use of apple pomace as a source

of dietary fiber in wheat bread. Journal of Food Processing and

Preservation 22, 255–263.

Meza, J.C., Christen, P., Revah, S., 1998. Effect of added amino acids

on the production of a fruity aroma by Ceratocystis fimbriata.

Sciences des Aliments 18, 627–636.

Nakata, B., 1994. Recycling by-products on California vineyards.

Biocycle 4, 61.

Namasivayam, C., Kanchana, N., 1992. Waste Banana Pith as

Adsorbent for color removal from wastewaters. Chemosphere 25

(11), 1691–1705.

Namasivayam, C., Kadirvelu, K., 1996. Uptake of mercury (II) from

wastewater by activated carbon from an unwanted agricultural

solid by-product: coirpith. Carbon 1073(SGML) C, 1–6.

Namasivayam, C., Kadirvelu, K., 1997. Activated carbons prepared

from coir pith by physical and chemical activation methods.

Bioresource Technology 62, 123–127.

Namasivayam, C., Muniasamy, N., Gayatri, K., Rani, M., Rangana-

than, K., 1996. Removal of dyes from aqueous solutions by

cellulosic waste orange peel. Bioresource Technology 57, 37–43.

Nambudiri, E.S., Shivashankar, S., 1985. Cocoa waste and its

utilization. Indian Cocoa, Arecanut and Spices Journal 8 (3), 78–

80.

Nanjundaswamy, A.M., 1997. Processing. In: R.E. Litz (Ed.), The

Mango, Botany, Production and Uses, Cab International, Wal-

lingford, pp. 535–539.

Nawar, S.S., Doma, H.L., 1989. Removal of dyes from effluents using

low-cost agricultural by-products. The Science of the Total

Environment 79, 271–279.

196 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198

Page 31: Vegetal Waste

Nicolet, L., Rott, U., 1999. Einsatz der Membranfiltration zur

Trennung von Pulveraktivkohle aus Wasser und Abwasser. In:

7th Aachener Membrankolloquium, 9–13.03.1999, (D), pp. 287–

290.

Nigam, J.N., 1999. Continuous ethanol production from pineapple

cannery waste. Journal of Biotechnology 72, 197–202.

Nigam, P., Armour, G., Banat, I.M., Singh, D., Marchant, R., 2000.

Physical removal of textile dyes from effluents and solid-state

fermentation of dye-adsorbed agricultural residues. Bioresource

Technology 72, 219–226.

Nwuha, V. et al., 1999. Solubility studies of green tea extracts in pure

solvents and edible oils. Journal of Food Engineering 40, 161–165.

Odozi, T., Emelike, R., 1985. The sorption of heavy metals with

corncob hydroxylate-red onion skin resins. Journal of Applied

Polymer Science 30, 2715–2719.

Ohsawa, K., Chinen, C., Takanami, S., Kuribayashi, T., Kurokouchi,

K., 1994. Studies on effective utilization of carrot pomace, 1:

Effective utilization to bread. Research Report of the Nagano State

Laboratory of Food Technology Japan (22), 24–28.

Ohsawa, K., Chinen, C., Takanami, S., Kuribayashi, T., Kurokouchi,

K., 1995. Studies on effective utilization of carrot pomace, 2:

Effective utilization to cake, dressing and pickles. Research Report

of Food Technology Research Institute of Nagano Prefecture,

Japan 4 (23), 15–18.

Omgbu, J.A., Iweanya, V.I., 1990. Dynamic sorption of Pb2þ and Zn2þ

ions with palm Elaesis guineensis kernel husk. Journal of Chemical

Education 67 (9), 800–801.

Pag�aan, J., Ibarz, A., 1999. Extraction and rheological properties of

pectin from fresh peach pomace. Journal of Food Engineering 39,

193–201.

Paul, D., Ohlrogge, K., 1998. Membrane separation processes for

clean production. Environmental progress 17 (3), 137–141.

Pendyal, B. et al., 1999. Removal of sugar colorants by granular

activated carbons made from binders and agricultural by-products.

Bioresource Technology 69, 45–51.

Peternele, W.S., Winkler-Hechenleitner, A.A., Pineda, E.A., 1999.

Adsorption of Cd(II) and Pb(II) onto functionalized formic

lignin from sugar cane bagasse. Bioresource Technology 68, 95–

100.

Prasertsan, S., Prasertsan, P., 1996. Biomass residues from palm oil

mills in Thailand: an overview on quantity and potential usage.

Biomass and Bioenergy 11 (5), 387–395.

Purchase, B., 1995. Products from sugarcane. International Sugar

Journal 97 (1154), 70–71.

Randall, J.M., Hautala, E., Waiss, A.C., 1974. Removal and

recycling of heavy metal ions from mining and industrial

waste streams with agricultural by-products. In: SO Proceed-

ings of Minerals Waste Utilization Symposium 4th. pp. 329–

334.

Randall, J.M., Reuter, F.W., Waiss, A.C., 1975. Removal of cupric ion

from solution by contact with peanut skins. Journal of Applied

Polymer Science 19, 1563–1571.

Rodriguez-Kabana, R., Estaun, V., Pinochet, J., Marfa, O., 1995.

Mixtures of olive pomace with different nitrogen sources for the

control of Meloidogyne spp. on tomato. Journal of Nematology 27

(45), 575–584.

Sans, C., Mata-Alvarez, J., Cecchi, F., Pavan, P., Bassetti, A., 1995.

Volatile fatty acids production by mesophilic fermentation of

mechanically-sorted urban organic wastes in a plug-flow Reactor.

Bioresource Technology 51 (1), 89–96.

Saura-Calixto, F., 1998. Antioxidant dietary fiber product: a new

concept and a potential food ingredient. Journal of Agricultural

and Food Chemistry 46 (10), 4303–4306.

Schr€ooder, T., 1999. Verkapselt und funktionell. Lebensmitteltechnik 6,

48–50.

Schutz, E. et al., 1982. Verfahren zur Extraktion der Aromastoffe aus

der Vanillekapsel, EP 0075134 A2.

Scott Kantor, L., Lipton, K., Manchester, A., Oliveira, V., 1997.

Estimating and addressing america’s food losses. Economic

Research Service, United States Department of Agriculture,

prepublished on the web. URL: http://151.121.66.126:80/whats-

new/feature/ARCHIVES/JULAUG97/INDEX.HTM.

Seibel, W., Hanneforth, U., 1994. Ballaststoffkonzentrate. Lebensmit-

teltechnik 4, 14–16.

Shukla, S.R., Sakhardande, V.D., 1990. Cupric ion removal by dyed

cellulosic materials. Journal of Applied Polymer Science 41, 2655–

2663.

Sigma, A., 2000. Flavors & Fragrances, Catalogue and Price list 2000.

Milwaukee, WI, USA.

Sreenath, H.K., Crandall, P.G., Baker, R.A., 1995. Utilization of

citrus by-products and wastes as beverage clouding agents. Journal

Of Fermentation And Bioengineering 80 (2), 190–194.

Srirangarajan, A.N., Shrikhade, A.J., 1976. Mango peel waste as a

source of pectin. Current science 45 (17), 620–621.

Sriroth, K. et al., 2000. Processing of cassava waste for improved

biomass utilization. Bioresource Technology 71, 63–69.

Stock, U., 1999. Am K€oorper der Suppe Wo kommt eigentlich der

Geschmack her? Die. ZEIT 52, 36, vom 22.12.99.

Stredansky, M., Conti, E., Stredanska, S., Zanetti, F., 2000. c-Linolenic acid production with Thamnidium elegans by solid-state

fermentation on apple pomace. Bioresource Technology 73, 41–

45.

Tagesschau vom 2.11.1999, Strom aus Kaffeesatz. HTML version der

Tagesschau/ARD, http://www.tagesschau.de/archiv/1999/11/02/

akruell/meldungen /kaffee?

Theobaudin, J.Y. et al., 1997. Dietary fibres: nutritional and techno-

logical interest. Trends in Food Science and Technology 8, 41–

48.

Thibault, J.F. et al., 1998. Fungal bioconversion of agricultural by-

products to vanillin. Lebensmittel, Wissenschaft und Technologie

31, 530–536.

Toles, C.A. et al., 2000. Acid-activated carbons from almond shells:

physical, chemical and adsorptive properties and estimated cost of

production. Bioresource Technology 71, 87–92.

Toma, R.B. et al., 1979. Physical and chemical properties of potato

peel as a source of dietary fiber in bread. Journal of Food Science

44, 1403–1407, 1417.

Torre, M., Rodriguez, A.R., Saura-Calixto, F., 1995. Interactions of

Fe(II), Ca(II) and Fe(III) with high dietary fibre materials: a

physicochemical approach. Food Chemistry 54 (1), 23–31.

Tran, C.T., Mitchell, D.A., 1995. Pineapple waste––a novel substrate

for citric acid production by solid-state fermentation. Biotechno-

logy Letters 17 (10), 1107–1110.

Tsai, W.T., Chang, C.Y., Lee, S.L., 1998. A low cost adsorbent from

agricultural waste corn cob by zinc chloride activation. Bioresource

Technology 64, 211–217.

Tuncel, G., Nout, M.J.R., Brimer, L., 1998. Degradation of cyano-

genic gycosides of bitter apricot seeds (Prunusi iarmeniacai) by

endogenous and added enzymes as affected by heat treatments and

particle size. Food Chemistry 63 (1), 65–69.

Turqouis, T., Rinaudo, M., Taravel, F.R., Heyraud, A., 1999.

Extraction of highly gelling pectic substances from sugar beet pulp

and potato pulp: influence of extrinsic parameters on their gelling

properties. Food Hydrocolloids 13, 255–262.

Urano, K., Tachikawa, H., Kitajima, M., 1992. Process development

for removal and recovery of phosphorus from wastewater by a new

adsorbent. 4. Recovery of phosphate and aluminium from desorb-

ing solution. Industrial Engineering and Chemical Research 31,

1513–1515.

Urano, K., Tachikawa, H., 1992. Process development for removal

and recovery of phosphorus from wastewater by a new ad-

sorbent. 3. Desorption of phosphate and regeneration of ad-

sorbent. Industrial Engineering and Chemical Research 31,

1510–1513.

G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198 197

Page 32: Vegetal Waste

Valiente, C., Arrigoni, E., Esteban, R.M., Amado, R., 1995. Grape

pomace as a potential food fiber. Journal of Food Science 60 (4),

818–820.

Vitolo, S., Petarca, L., Bresci, B., 1998. Treatment of olive oil industry

wastes. Bioresource Technology 67 (2), 129–137.

Vlyssides, A.G., Loizidou, M., Zorpas, A.A., 1999. Characteristics of

solid residues from olive oil processing as bulking material for co-

composting with industrial wastewaters. Journal of Environment,

Science and Health 34 (3), 737–748.

Vollbrecht, D., 1997. Feststoff-Fermentation-Ein historischer €UUberb-

lick. Chemie Ingenieur Technik 69 (10), 1403–1408.

Wang, J. et al., 1997. Continuous countercurrent extraction of pectin

from sunflower heads. Transactions of the ASAE 40 (6), 1649–

1654.

Widmer, W., Montanari, A.M., 1995. Citrus waste streams as a source

of phytochemicals. In: 107th Annual Meeting of the Florida State

Horticultural Society, Orlando/Florida, USA, vol. 107. pp. 284–

288.

Xie, J.Z., Chang, H.-L., Kilbane II, J.J., 1996. Removal and

recovery of metal ions from wastewater using biosorbents and

chemically modified biosorbents. Bioresource Technology 57, 127–

136.

ZDF.MSNBC vom 10.03.00, Reinheitsgebot f€uur Schokolade f€aallt.

Internetseite des ZDF, http://www.zdf.msnbc.de/news/50614.asp.

Zeller, B.L., 1999. Development of porous carbohydrate food ingre-

dients for the use in flavour encapsulation. Trends in Food Science

and Technology 9 (11–12), 389–394.

Zheng, Z., Shetty, K., 1998. Cranberry processing waste for solid state

fungal inoculant production. Process Biochemistry 33 (3), 323–329.

Zia-ur-Rehman, Ali, S., Khan, A.D., Shah, F.H., 1994. Utilisation of

fruit and vegetable wastes in layers diet. Journal of Science in Food

Agriculture 65 (4), 381–383.

198 G. Laufenberg et al. / Bioresource Technology 87 (2003) 167–198