Fruit Powders

PREETI BIRWAL

PH.D (DE)

ICAR-NDRI

Introduction

The popularity of fruits may be attributed to consumer perception oftheir health benefits.

In the case of fruit juices, many consumers are now looking for healthyalternatives to the traditional carbonated beverages.

Fruits are rich in dietary fibre as well as phytonutrients, especiallyantioxidants, and have no cholesterol.

The availability in the market of natural fruit juices derived from freshfruits is a welcome alternative

Fruits are important sources of vitamins and carbohydrates. They arenaturally sweet and low in calories. Different fruits contain different typeof vitamins, so it is important to have a variety of fruits.

Fruits are the important intake of our daily diet life. There is no cause ofside effect by fruits because it provides necessary vitamins to our body.The vitamins are important to humans for providing energy to awayfrom various kinds of sickness

Fruit Powder

The powder can be used as an ingredient for cooking food or as a

flavoring agent in some products. Its advantages consist of

(a) a long shelf life at ambient temperature due to low water

activity,

(b) low logistic expenditures due to little weight and volume, and

(c) vast multi disciplinary uses.

One of the widely spread methods of preserving such products

consists in drying both fruits and berries as well as organization of

production of various kinds of the new products in a form ofpowders either from juices and extracts ( totally soluble) or powders

obtained from whole fruits including cellular tissue and other

components of fruits which undergo processing to two directions are:

I- production of soluble fruit-dairy powders by spray drying;

2- production of fruit and vegetable powders by convective

drying.

The drying of pure (without any additives) juices from fruits is quite Complex. It is determined primarily by the thermoplastic properties of the drying material as well as the considerably hygroscopic nature of the powder-like product.

Chemical composition of juices is very complex too, approx. 90% of dry substances in juices and purees made up of hydrocarbons: monosaccharides (glucose, fructose), disaccharides (saccharose) and polysaccharides.

To the nutrient substances are added hydrocarbons, nitrogen containing substances, organic acids, plyphenol substances, vitamins etc. Under the influence of temperature and air oxygen inside the spray drying chamber various complicated transformations of component substances may take place which reveal themselves in changing of color and decrease of the nutrient quality.

Steps

Sorting

Grading

Cleaning

Sulphating

Alkaline dip

Blanking

Juice extraction

Clarification

Filtration

Juice concentration

Drying

Drying

Drum Drying

Spray Drying

Freeze Drying

Microwave and dielectric Drying

Spouted Bed Drying

Pneumatic and Flash Drying

Superheated Steam Drying

Fluidization Bed drying

Foam Drying

Rotary

Belt and Tunnel Drying

Fruits and Vegetables

Fruit puree( Grapes, apple,

cherry)

Grape juice

Lime juice

Pear juice

Pineapple juice

Mango juice

Orange juice

Citrus juices

Blueberry juice

Beetroot juice

Carrot juice

Passion fruit juice

Acerola juice

Coconut juice

Other vegetable juices

Dryer Selection Chart

A guide to dyer selection

FORMULATION AND EVALUATION OF A POWDER

Production of powder by drum dryer using maltodextrin and Arabic

gum as adjuncts

MD were preferred in facet of appearance, color, and overall liking,

while those with AG were favored in their aroma and taste.

Micro-encapsulated powders

Sugar-rich products

Fruit powder is just one step past drying fruit, too; after a brief

conditioning phase, all you have to do is pulverize it. For best color, taste and texture, use the freshest, ripest fruit available.

Powder characteristics

Bulk density

Particle morphology

Angle of repose

Wettability

Dispersion

Solubility

Moisture content

Free flowing

Fine

Dustless

Granules

Agglomerated

Lumps

Hygroscopic

Hydrophobic

Thermoplastic

A typical

two-

stage

spray

dryer

Source: Dairy Processing Handbook.

Published by Tetra Pak Processing

Systems AB, S-221 86 Lund, Sweden.

pg. 369.

Operating conditions

Electricity heater heated inlet air until 80-200°C.

when outlet air temperature was in the range of 100-110°C.

Rotary atomizer with 25000-rpm speed.

Cyclone with effective diameter 10 cm separated the air-powder

mix.

The ambient air ambient temperature is about 20-25°C and relative

humidity of 35-45%.

0.5-0.8 g cm3 density.

Source: Dairy

Processing

Handbook.

Published by Tetra

Pak Processing

Systems AB, S-221 86

Lund, Sweden. pg.

370.

FILTERM

AT

DRYER

Factors Affecting Powder Properties

Inlet temperature

Powder properties such as moisture content, bulk density, particle size,

hygroscopicity and morphology were affected by inlet temperature.

It was found that at a constant feed flow rate, increasing the inlet air

temperature reduced the residual moisture content.

Increased temperature caused the reduction in bulk density. An

increase in the inlet air temperature often results in a rapid formation of

dried layer on the droplet surface and particle size and it causes the

skinning over or casehardening on the droplets at the higher

temperatures. This leads to the formation of vapor-impermeable films

on the droplet surface, followed by the formation of vapor bubbles

and, consequently the droplet expansion increase of drying air

temperature generally causes the decrease in bulk, particle density

and provides the greater tendency to the particles to hollow

higher inlet air temperature leads to the production of larger

particles and causes the higher swelling.

The higher drying temperature is lower the moisture content and

increase its hygroscopicity (its capacity to absorb ambient

moisture). This is related to the water concentration gradient

between the product and the surrounding air, which is great for the

less moist powder.

On the other hand, the increase of inlet air temperature has

reduced the yield and it might be caused by melting of the powder

and cohesion wall and therefore the amount of powder production

and yield was reduced

When the inlet air temperature was low, the particles showed a

shriveled surface, while increasing drying temperatures resulted in a

larger number of particles with smooth surface.

Air flow rate

The increased residence time led to the greater degree of moisture

removal.

As a result, an increase of the drying air flow rate, decrease theresidence time of the product in the drying chamber and it leads to

have higher moisture contents.

In addition, the effect of drying air flow rate of powder bulk density

depends on its effect on moisture content due to the sticky nature

of the product.

Atomizer speed

The residual moisture content was decreased when increasing the

atomizer speed.

At higher atomizer speed, the smaller droplets were produced and more moisture was evaporated resulting from an increased contact

surface.

Feed flow rates

Higher flow rates imply in a shorter contact time between the feed

and drying air and making the heat transfer less efficient and thus

caused the lower water evaporation.

The higher feed flow rate showed a negative effect on process yield

and that was resulting the decreased heat, mass transfer and the

lower process yield. In addition, when higher feed rates were used,

a dripping inside the main chamber was observed, when the

mixture was passed straight to the chamber and that was not

atomized and finally resulting the lower process yield.

Type of carrier agent

The result showed that the higher the maltodextrin dextrose

equivalent (DE) causes higher the moisture content in the powder.

This probably due to the chemical structure of high-DE maltodextrins, which have a high number of ramifications with

hydrophilic groups, and thus can easily bind to water molecules

from the ambient air during powder handling after the spray drying.

Additionally, higher maltodextrin DE caused the increase in bulk

density in the powder due to its stickiness.

The higher maltodextrin DE was produced the lower glass transition

temperature and it lower the elevation of the Tg in fruit pulp-maltodextrin mixture

The result was revealed that the particles produced with

maltodextrin 10DE showed the lowest moisture adsorption rate,

while the samples were produced with maltodextrin 20DE and gum Arabic had more hygroscopic and with faster water adsorption and

the lower moisture in the powders

The different type of carrier agent was having the variance in

powder solubility

Problems

Some researchers claimed that drying of fruit juice could producethe fruit powder that reconstituted rapidly to a fine productresembling the original juice.

Nonetheless, there are some difficulties in drying the fruit juice withhigh sugar content due to their thermoplasticity and hygroscopicityat high temperatues and humidity levels causing their packagingand utilization in trouble

These characteristics are attributed to low molecular weight sugarssuch as fructose, glucose and sucrose and organic acids such ascitric, malic and tartaric that are the major solids in fruit juices

The low glass transition temperature (Tg), high hydroscopy, lowmelting point, and high water solubility of these solids lead to highlysticky or rubbery product when dried

Natural hygroscopic and thermoplastic property physical properties

of fruit juice aided to drying.

These of fruit juice is the basis problem in transport and agent materials include corn syrup; natural gums, sucrose, handling of fruit

juice powder produced in spray malt dextrin etc…caused powder

production and prevent dryer agent materials include corn syrup;

natural gums, sucrose, malt dextrin

The drum drying parameters such as

drying temperature,

Feed rate,

rotation speed,

feed concentration, and

surrounding air condition

are influential to the attributes of drum-dried food such as particle size,

bulk density, moisture content, and solubility

Stickiness issues during spray drying

• Stickiness on the drier wall (spray drying)

• Wet and plastic appearance

• Agglomeration and clumping in packing container

• Operational problems

• Losses

Sticky

product

Hot air

Non-sticky

product

Products exhibiting stickiness during drying

• Products with high amount of sugars or organic

acids

– Fruit juices/pieces/purees/leathers

– Honey

– Molasses

– Whey (acid or sweet)

– High DE maltodextrins (DE>30)

– Pure sugars- glucose, sucrose, fructose

– High acid foods

• High fat foods

Major factors causing stickiness

• High hygroscopicity

• High solubility

• Low melting point temperature

• Low glass transition temperature

(related to thermoplasticity)

What is a glass transition?

– Amorphous

• non-aligned molecular structure

• very hygroscopic

• go through glass transition

• predominant in dried food

– Crystalline

• aligned molecular structure

• non hygroscopic

• no glass transition

Physical states of dried solid materials

Semi-crystalline solid Liquid solution

Grinding

Extrusion cooking

Thermal melting & cooling

Rapid water

removal- drying

Rapid cooling below Tg

water <-135oC

honey <-45oC

Amorphous solid

(glass)

Crystalline solid

Solid Liquid

Glass transition

Stickiness

Property of an amorphous solid

_______________________________________________________

Food materials Tg (oC)abc

_______________________________________________________

Fructose 14

Glucose 31

Galactose 32

Sucrose 62

Maltose 87

Lactose 101

Citric acid 6

Tartaric acid 18

Malic acid -21

Lactic acid -60

Maltodextrins

DEd

36 (MW=550) 100

DE 25 (MW=720) 121

DE 20 (MW=900) 141

DE 10 (MW=1800) 160

DE 5 (MW=3600) 188

Starch 243e

Ice-cream f -34.3

Honeyg -42 to -51

Glass transition temperature of various food materials

Spray drying of sticky product

some guideline

• Drying below the glass transition temperature (often

not feasible)

• Mild drying temperature conditions

• Increasing the Tg by adding high molecular weight

materials (such as maltodextrins)- a predictive

approach needed according to the composition

• Immediate cooling of the product below its Tg

• Appropriate drier design to suit the sticky product

The thermoplasticity and hygroscopicity troubles occurring in drying the fruit

juice with high sugar content can be overcome by adding some drying carriers such as maltodextrin (MD) and Arabic gum (AG).

These drying adjuncts are high molecular weight compounds that have high

Tg , accordingly, they can raise the Tg Value of feed and the subsequent

powder.

MD is the most popular in spray drying due to its physical properties such as

high water solubility; while, AG is recommended

For fruit juice drying due to its emulsification properties and ease of dissolution

in water.

MD consists of b-D-glucose units linked mainly by glycosidic bonds and are

typically classified by their dextrose equivalent (DE).

MD could improve the stability of fruit powder with high sugar content

because it reduced the stickiness and agglomeration problems during storage.

Dust Prevention

Dust generation can lead to a number of problems for food powders.

These can be summarised as follows:

(i) Health problems, in particular allergy problems;

(ii) (ii) contamination and plant hygiene issues due to dust settling and

sticking onto equipment; and (iii) fire/explosion hazards.

(iii) Sensors for measuring carbon-monoxide have been developed

and are already industrially implemented in the dairy industry

Changes during Storage

Loss of vitamins

Loss of natural pigments

Browning reaction and rill of sulphrous groups

Oxidative degradation and flavor loss

Texture and reconstitute ability

Glass transition point

Microbiological hazard