Post on 04-Mar-2015
Application of cereals and cereal components in
functional foods: a review
D. Charalampopoulos, R. Wang, S.S. Pandiella *, C. Webb
Department of Chemical Engineering, Satake Centre for Grain Process Engineering, UMIST, Manchester M60 1QD, UK
Received 15 March 2002; received in revised form 23 April 2002; accepted 25 April 2002
Abstract
The food industry is directing new product development towards the area of functional foods and functional food ingredients
due to consumers’ demand for healthier foods. In this respect, probiotic dairy foods containing human-derived Lactobacillus and
Bifidobacterium species and prebiotic food formulations containing ingredients that cannot be digested by the human host in the
upper gastrointestinal tract and can selectively stimulate the growth of one or a limited number of colonic bacteria have been
recently introduced into the market. The aim of these products is to affect beneficially the gut microbial composition and activities.
Cereals offer another alternative for the production of functional foods. The multiple beneficial effects of cereals can be exploited
in different ways leading to the design of novel cereal foods or cereal ingredients that can target specific populations. Cereals can
be used as fermentable substrates for the growth of probiotic microorganisms. The main parameters that have to be considered are
the composition and processing of the cereal grains, the substrate formulation, the growth capability and productivity of the starter
culture, the stability of the probiotic strain during storage, the organoleptic properties and the nutritional value of the final product.
Additionally, cereals can be used as sources of nondigestible carbohydrates that besides promoting several beneficial physiological
effects can also selectively stimulate the growth of lactobacilli and bifidobacteria present in the colon and act as prebiotics. Cereals
contain water-soluble fibre, such ash-glucan and arabinoxylan, oilgosaccharides, such as galacto- and fructo-oligosaccharides andresistant starch, which have been suggested to fulfil the prebiotic concept. Separation of specific fractions of fibre from different
cereal varieties or cereal by-products, according to the knowledge of fibre distribution in cereal grains, could be achieved through
processing technologies, such as milling, sieving, and debranning or pearling. Finally, cereal constituents, such as starch, can be
used as encapsulation materials for probiotics in order to improve their stability during storage and enhance their viability during
their passage through the adverse conditions of the gastrointestinal tract. It could be concluded that functional foods based on
cereals is a challenging perspective, however, the development of new technologies of cereal processing that enhance their health
potential and the acceptability of the food product are of primary importance.
D 2002 Elsevier Science B.V. All rights reserved.
Keywords: Cereals; Probiotic; Prebiotic; Fermentation; Lactic acid bacteria; Bifidobacteria
1. Introduction
The interest in developing functional foods is thriv-
ing, driven largely by themarket potential for foods that
can improve the health and well-being of consumers.
The concept of functional foods includes foods or food
0168-1605/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.
PII: S0168 -1605 (02 )00187 -3
* Corresponding author. Tel.: +44-161-200-4429; fax: +44-161-
200-4399.
E-mail address: s.pandiella@umist.ac.uk (S.S. Pandiella).
www.elsevier.com/locate/ijfoodmicro
International Journal of Food Microbiology 79 (2002) 131–141
ingredients that exert a beneficial effect on host health
and/or reduce the risk of chronic disease beyond basic
nutritional functions (Huggett and Schliter, 1996).
Successful types of functional products that have been
designed to reduce high blood pressure, cholesterol
blood sugar, and osteoporosis have been introduced
into the market (Sanders, 1998). Recently, the func-
tional food research has moved progressively towards
the development of dietary supplementation, introduc-
ing the concept of probiotics and prebiotics, which may
affect gut microbial composition and activities (Ziemer
and Gibson, 1998).
Probiotic foods are defined as those that contain
a single or mixed culture of microorganisms that
affect beneficially the consumer’s health by improv-
ing their intestinal microbial balance (Fuller, 1989).
There is significant scientific evidence, based
mainly on in vitro studies and on clinical trials
using animals, suggesting the potentially beneficial
effects of probiotic microorganisms. These include:
metabolism of lactose, control of gastrointestinal
infections, suppression of cancer, reduction of
serum cholesterol, and immune stimulation (Gilli-
land, 1990; Salminen et al., 1998; Fooks et al.,
1999). The necessity for epidemiological studies on
healthy human populations to support the specific
health promoting claims of a probiotic strain is
generally highlighted (Sanders, 1998; Shortt, 1999;
Saarela et al., 2000). Common microorganisms used
in probiotic preparations are predominantly Lacto-
bacillus species, such as Lactobacillus acidophilus,
L. casei, L. reuteri, L. rhamnosus, L. johnsonii, and
L. plantarum and Bifidobacterium species, such as
Bifidobacterium longum, B. breve, B. lactis (Shortt,
1999). The incorporation of probiotic strains in
traditional food products has been established in
the dairy industry, leading to the production of
novel types of fermented milks and cheeses (Gomes
and Malcata, 1999).
A prebiotic is a food ingredient that is not
hydrolysed by the human digestive enzymes in
the upper gastrointestinal tract and beneficially
affects the host by selectively stimulating the
growth and/or activity of one or a limited number
of bacteria in the colon that can improve host
health (Gibson and Roberfroid, 1995). Fibre is a
general term of different types of carbohydrates
derived from plant cell walls that are not hydro-
lysed by human digestive enzymes. Specific forms
of dietary fibre are readily fermentable by specific
colonic bacteria, such as bifidobacteria and lactoba-
cilli species, increasing their cell population with
the concomitant production of short-chain fatty
acids (SCFA). These acids, especially butyrate,
acetate, and propionate, provide metabolic energy
for the host and acidification of the bowel (Sghir et
al., 1998). Several clinical studies have also sug-
gested that dietary fibre could promote beneficial
physiological effects including laxation and blood
cholesterol attenuation (Spiller, 1994), as well as
blood glucose attenuation (Bijlani, 1985). It may
also prevent cancer (McCann et al., 2001), diabetes
(Wang et al., 2001), heart disease (Fernandez,
2001), and obesity (Iwata and Ishiwatari, 2001).
However, epidemiological results have to be treated
with great precaution due to the complexity of the
possible mechanisms involved.
2. Cereal-based functional products
The development of nondairy probiotic products is
a challenge to the food industry in its effort to utilise
the abundant natural resources by producing high
quality functional products. In this respect, probi-
otic-containing baby foods or confectionery formula-
tions have been developed by adding the strains as
additives (Saarela et al., 2000). In recent years, cereals
have also been investigated regarding their potential
use in developing functional foods. Cereals are grown
over 73% of the total world harvested area and
contribute over 60% of the world food production
providing dietary fibre, proteins, energy, minerals, and
vitamins required for human health. The possible
applications of cereals or cereal constituents in func-
tional food formulations could be summarised:
� as fermentable substrates for growth of probiotic
microorganisms, especially lactobacilli and bifido-
bacteria� as dietary fibre promoting several beneficial
physiological effects� as prebiotics due to their content of specific
nondigestible carbohydrates� as encapsulation materials for probiotic in order to
enhance their stability.
D. Charalampopoulos et al. / International Journal of Food Microbiology 79 (2002) 131–141132
3. Cereals as substrates for probiotics
Lactic acid fermentation of cereals is a long-estab-
lished processing method and is being used in Asia
and Africa for the production of foods in various
forms such as beverages, gruels, and porridge.
Although differences exist between regions, the prep-
aration procedure could be generalised. Cereal grains,
mainly maize, sorghum, or millet grains, are soaked in
clean water for 0.5–2 days. Soaking softens the grains
and makes them easier to crash or wet-mill into slurry,
from which hulls, bran particles, and germs can be
removed by sieving procedures. During the slurring or
doughing stage, which lasts for 1–3 days, mixed
fermentations including lactic acid fermentation take
place. During the fermentation, the pH decreases with
a simultaneous increase in acidity, as lactic and other
organic acids accumulate due to microbial activity.
InWestern countries, cereals, like wheat and rye, are
used for sourdough production, which is traditionally
prepared by adding a prefermented sourdough of good
quality to the dough. These starter cultures can be
characterised as ‘mixed-strain cultures’ and are con-
tinuously propagated and distributed in small propor-
tions in bakeries. The population of lactobacilli in fully
fermented sourdoughs is more than 109 cfu g� 1, while
the lactic acid bacteria (LAB)/yeast ratio is generally
100:1 (Salovaara, 1998).
The good growth of LAB in cereals suggests that
the incorporation of a human-derived probiotic strain
in a cereal substrate under controlled conditions
would produce a fermented food with defined and
consistent characteristics, and possibly health-promot-
ing properties combining the probiotic and prebiotic
concept. However, in designing such a novel fermen-
tation food process, several technological aspects have
to be considered such as the composition and process-
ing of the cereal grains, the growth capability and
productivity of the starter culture, the stability of the
probiotic during storage, the organoleptic properties,
and the nutritional value of the final product.
3.1. Effect of cereal composition on growth of
probiotics
Probiotic products are usually standardised based on
the presumption that culture viability is a reasonable
measure of probiotic activity, thus the ability of the
strain to attain high cell population is of primary
importance. A concentration of approximately 107 cells
ml� 1 at the time of consumption is considered func-
tional (Gomes and Malcata, 1999; Shortt, 1999). High
cell growth rates and acidification rates would also re-
sult in reduction of fermentation times and enhance the
viability of the specific strain by preventing growth of
undesirable microorganisms present in the rawmaterial
(Marklinder and Lonner, 1992), which would lead to
the formation of off-flavours (Svensson, 1999). There-
fore, the adaptability of the probiotic in the substrate is a
very important criterion in the selection procedure of a
suitable strain (Oberman and Libudzisz, 1998).
Lactobacilli and bifidobacteria have complex nutri-
tional requirements such as carbohydrates, amino
acids, peptides, fatty esters, salts, nucleic acid deriva-
tives, and vitamins, which vary a lot from species to
species (Severson, 1998). The principal carbohydrate
constituents of cereal grains are starch, water-soluble or
-insoluble components of dietary fibre, and several free
sugars, such as glucose, glycerol, stachyose, xylose,
fructose, maltose, sucrose, and arabinose. The contents
of these components depend on the variety (Becker and
Hanners, 1991), the processing, and the amount of
water addition. Table 1 presents the composition of
different varieties of cereals compared to that of milk.
Cereals have higher content of some of the essential
vitamins than milk, higher content of dietary fibre, and
increased amount of minerals, especially phosphorus,
but lower amount of fermentable carbohydrates, usu-
ally less than 1% in wheat dough.
Information concerning the effects of cereal compo-
sition on the growth of probiotic microorganisms is
limited. Marklinder and Lonner (1992) suggested the
potential of fermented oatmeal soup (18.5%) contain-
ing viable LAB as a base for nutritive solution in enteral
feeding. After testing several heterofermentative and
homofermentative probiotic lactobacilli, it was con-
cluded that oats are in general a suitable substrate for
LAB growth, regardless of the differences between
species and strains. Among the strains tested, L. acid-
ophilus exhibited the slowest rates of pH reduction, and
lowest levels of viable cells in the final product, due
probably to its high requirements for several nutrients
(Morishita et al., 1981). The highest viable cell counts,
3� 109 and 1�109 cfu ml� 1, were achieved using L.
plantarum and L. reuteri, respectively. Addition of
malted barley flour, proteases and amino acids
D. Charalampopoulos et al. / International Journal of Food Microbiology 79 (2002) 131–141 133
increased the rate of pH-decrease and the total amount
of lactobacilli in the final product (Marklinder and
Lonner, 1994). In a similar study, L. acidophilus was
successfully cultivated in an enzymatically hydrolysed
oat mash reaching 109 cfu ml� 1 (Bekers et al., 2001).
In our study (Charalampopoulos et al., 2002),
human-derived strains of L. reuteri, L. plantarum, L.
acidophilus, and a L. fermentum strain isolated from
cereals were cultured in malt, barley, and wheat
extracts formulated without the addition of any sup-
plements. The growth parameters are presented in
Table 2. The malt medium supported better cell
growth than barley and wheat due to the increased
amounts of maltose, sucrose, glucose, and fructose
(approximately 15 g l � 1 of total fermentable sugars)
and free amino nitrogen (approximately 80 mg l � 1).
It must be emphasised that each strain demonstrated a
specific preference for one or more sugars, which has
been reported for LAB isolated from fermented cereal
products (Gobbetti and Corsetti, 1997). The similar
fermentation patterns observed in wheat and barley
for all the strains tested could be attributed to the low
total fermentable sugar (3–4 g l � 1) and the low free
amino nitrogen concentration (15.3–26.6 mg l � 1). L.
plantarum exhibited the highest cell population owing
to its unique ability to tolerate low pH values by
Table 1
Composition of foods expressed as 100 g of edible portion
Parameter Malt Rice Corn Wheat Sorghum Millet Milk (liquid)
Water (%) 8 12 13.8 12 11 11.8 87.4
Protein (g) 13.1 7.5 8.9 13.3 11 9.9 3.5
Fat (g) 1.9 1.9 3.9 2.0 3.3 2.9 3.5
Carbohydrates (g) 77.4 77.4 72.2 71.0 73.0 72.9 4.9
Fiber (g) 5.7 0.9 2.0 2.3 1.7 3.2 n.d.
Ash (g) 2.4 1.2 1.2 1.7 1.7 2.5 0.7
Ca (mg) 40 32 22 41 28 20 118
P (mg) 330 221 268 372 287 311 93
Fe (mg) 4.0 1.6 2.1 3.3 4.4 68 Trace
K (mg) 400 214 284 370 350 430 144
Thiamin (mg) 0.49 0.34 0.37 0.55 0.38 0.73 0.03
Riboflavin (mg) 0.31 0.05 0.12 0.12 0.15 0.38 0.17
Niacin (mg) 900 1.7 2.2 4.3 3.9 2.3 0.1
Mg (mg) 140 88 147 113 n.d. 162 13
Source: Adapted from Severson (1998).
Table 2
Numerical values of estimated microbial growth parameters in sterile malt, barley, and wheat media
Medium Microorganism lmax (h� 1) X0 (log10cfu ml� 1) Xmax (log10 cfu ml� 1) pH
Malt L. fermentum 0.62F 0.04 6.85F 0.08 9.68F 0.03 3.77F 0.09
L. plantarum 0.41F 0.03 6.90F 0.10 10.11F 0.18 3.40F 0.09
L. reuteri 0.38F 0.02 6.20F 0.07 8.86F 0.06 3.72F 0.09
L. acidophilus 0.19F 0.02 6.89F 0.06 8.10F 0.06 3.73F 0.09
Barley L. fermentum 0.43F 0.05 6.90F 0.11 9.12F 0.05 4.61F 0.09
L. plantarum 0.20F 0.02 6.71F 0.13 9.43F 0.10 3.92F 0.09
L. reuteri 0.13F 0.01 6.14F 0.04 7.28F 0.05 4.88F 0.09
L. acidophilus 0.18F 0.03 7.02F 0.04 7.73F 0.03 3.93F 0.09
Wheat L. fermentum 0.53F 0.05 6.93F 0.09 9.28F 0.04 4.50F 0.09
L. plantarum 0.23F 0.02 7.21F 0.05 9.29F 0.06 3.83F 0.09
L. reuteri 0.13F 0.01 6.22F 0.03 7.20F 0.04 4.40F 0.09
L. acidophilus 0.15F 0.01 7.02F 0.02 7.71F 0.03 3.73F 0.09
lmax =maximum specific growth rate, X0 = initial cell population, X max =maximum cell population at the end of the exponential phase, pH= pH
at the end of the exponential phase.
The maximum specific growth rate was estimated using a logistic-type equation, applied to the data obtained during growth.
Source: Adapted from Charalampopoulos et al. (2002).
D. Charalampopoulos et al. / International Journal of Food Microbiology 79 (2002) 131–141134
maintaining a proton (pH) and charge gradient
between the inside and the outside of the cells even
in the presence of high amounts of lactate and protons
(Giraud et al., 1998). L. acidophilus exhibited the
poorest growth probably because of substrate defi-
ciency in specific nutrients, confirming the impor-
tance of substrate composition in conjunction with the
nutritional requirements of the specific strain.
3.2. Survival of probiotics
A key factor in the selection of suitable probiotic
starter is its ability to survive the acidic environment of
the final fermented product (in vitro) and the adverse
conditions of the gastrointestinal tract (in vivo). The
survival of the probiotic bacteria in vitro might be
influenced by the metabolites formed by the starter
such as lactic acid and acetic acid, hydrogen peroxide,
and bacteriocins (Saarela et al., 2000). Although differ-
ences exist between species and specific strains, lacto-
bacilli are generally considered to be intrinsically
resistant (Kashket, 1987), especially at pH values
higher than 3.0 (Hood and Zottola, 1988; Jin et al.,
1998). Of the various probiotic bacteria, L. casei and L.
plantarum appear to have longer shelf lives than L.
acidophilus, L. reuteri, and bifidobacteria in cultured
milk (Lee and Salminen, 1995). Based on the above,
the optimum final pH and the concentrations of lactic
acid and acetic acid in fermented cereal product in
relation to the properties of each specific probiotic
strain have to be investigated in order to maximise
the viability during storage. Besides the intrinsic stabil-
ity of each strain, the inclusion of slow-metabolising
energy sources, such as arginine, fructose, citric acid,
and malic acid, which could be present in cereals, has
been reported to enhance the viability by providing
energy (Lee and Salminen, 1995).
Survival of the probiotic strains during gastric
transit is also influenced by the physicochemical
properties of the food carrier used for delivery. The
buffering capacity and the pH of the carrier medium
are significant factors, since food formulations with
pH ranging from 3.5 to 4.5 and high buffering
capacity would increase the pH of the gastric tract
and thus enhance the stability of the probiotic strain
(Kailasapathy and Chin 2000; Zarate et al., 2000). In
addition, it has been shown that malt, wheat, and
barley extracts exhibited a significant protective effect
on the viability of human-derived L. plantarum and L.
acidophilus strains under acidic conditions mimicking
the stomach, which based on supporting experiments
with dietary constituents could be mainly attributed to
the presence of soluble sugars in the cereal extracts
and to a less extent to the free amino nitrogen content,
depending on the strain. (Charalampopoulos et al.,
data not shown).
3.3. Organoleptic properties
The grains of corn, sorghum, millet, barley, rye,
and oats contain appreciable amount of crude fibre
and lack gluten-like proteins of wheat. The traditional
foods made from these grains usually lack flavour and
aroma (Chavan and Kadam, 1989). Lactic acid fer-
mentation improves the sensorial value, which is very
much dependent on the amounts of lactic acid, acetic
acid and several aromatic volatiles, such as higher
alcohols and aldehydes, ethyl acetate and diacetyl,
produced via the homofermentative or heterofermen-
tative metabolic pathways. Consequently, an appro-
priate selection of the strain is necessary to efficiently
control the distribution of the metabolic end products
(Lonner and Preve-Akesson, 1988; Damiani et al.,
1996; Hansen et al., 1989). Knowledge of the bio-
chemical pathways leading to flavour production can
help in making the right choice of starter. However,
the end product distribution of lactic acid fermenta-
tions depends also on the chemical composition of the
substrate (carbohydrate content, presence of electron
acceptors, nitrogen availability) and the environmen-
tal conditions (pH, temperature, aeorbiosis/anaerobio-
sis), controlling of which would allow specific
fermentations to be channelled towards a more desir-
able product (Hansen and Hansen, 1994).
In general, probiotic products obtained using a
single strain probiotic starter are hardly acceptable to
consumers, lacking sensory appeal due to a rather sour
and acidic taste. For milk-based products, the probiotic
strains are often mixed with Streptococcus thermophi-
lus and L. delbrueckii (Saarela et al., 2000). In this
respect, another alternative in enhancing the aromatic
profile of the final product would be the incorporation
of supporting strains being able to bring out the
preferred flavour. It is important that the supporting
strains grow in the cereal substrate and do not act
antagonistically towards the probiotic strain. In indus-
D. Charalampopoulos et al. / International Journal of Food Microbiology 79 (2002) 131–141 135
trial cereal fermentations L. sanfransisco, the most
important sourdough bacteria, is usually mixed with
Sacharomyces exiguus or Candida milleri, improving
the overall organoleptic properties (Gobbetti, 1998).
3.4. Nutritional value
Lactic acid fermentation improves usually the nutri-
tional value and digestibility of cereals. Cereals are
limited in essential amino acids such as threonine,
lysine, and tryptophan, thus making their protein qual-
ity poorer compared with animals and milk (Chavan
and Kadam, 1989). Their protein digestibility is also
lower than that of animals, due partially to the presence
of phytic acid, tannins, and polyphenols which bind to
protein thus making them indigestible (Oyewole,
1997). Lactic acid fermentation of different cereals,
such as maize, sorghum, finger millet, has been found
effectively to reduce the amount of phytic acid, tannins
and improve protein availability (Chavan et al., 1988;
Lorri and Svanberg, 1993). Increased amounts of ribo-
flavin, thiamine, niacin, and lysine due to the action of
LAB in fermented blends of cereals were also reported
(Hamad and Fields, 1979; Sanni et al., 1999). Khetar-
paul and Chauhan (1990) reported improved minerals
availability of pearl millet fermented with pure cultures
of lactobacilli and yeasts.
4. Dietary fibre from cereal grains and their
prebiotic and physiological effects
4.1. Definition
Dietary fibre is the edible part of plants or analo-
gous carbohydrates, which resists the hydrolysis by
alimentary tract enzymes. In addition, fibre is not
totally unavailable either, because a portion of dietary
fibre is metabolised to volatile fatty acids in the
gastrointestinal tract. Dietary fibre can be divided into
two categories according to their water solubility.
Each category provides different therapeutic effects.
Water-soluble fibre consists mainly of nonstarchy
polysaccharides, mainly h-glucan and arabinoxylan.
By forming viscous solution, soluble fibre slows
intestinal transit, delays gastric emptying, and reduces
glucose and sterol absorption by the intestine. Soluble
fibre also decreases serum cholesterol, prostprandial
blood glucose, and insulin contents in human body.
Water-insoluble fibre contains lignin, cellulose, hemi-
celluloses (Bingham, 1987; Marlett, 1990), and non-
starchy polysaccharides such as water-unextractable
arabinoxylan.
Between cereal grains, the content of dietary fibre
varies (Table 3) (Nelson, 2001; Herrera et al., 1998).
In cereal botanical components, the majority of diet-
ary fibres generally occur in decreasing amounts from
the outer pericarp to the endosperm, except arabinox-
ylan, which is also a major component of endosperm
cell wall materials. The procedures for the isolation
and purification of dietary fibre and the techniques
involved in their quantitative and structural analysis
were developed for the isolation of dietary fibre from
conventional milling streams. The combination of the
debranning or pearling technology and the subsequent
simplified milling process might produce processing
streams of more specified botanical components, such
as the outer pericarp, the inner pericarp, the seed coat,
the aleurone cells, the embryo, and the starchy endo-
sperm. Targeting at particular dietary fibres in each of
these streams according to the knowledge of fibre
distribution in cereal grains, these isolation procedures
would be simplified and their products more purified.
4.2. b-Glucan
One of the most important members of the dietary
fibre family is h-glucan. It is unbranched polysac-
charides composed of (1! 4) and (1! 3) linked h-D-glucopyranosyl units in varying proportions. Various
forms of h-glucan have been recognised as having
Table 3
Comparison of total dietary fibre content in cereal grains
Cereals Total dietary fibre (%, db)
Legumes 13.6–28.9
Rye 15.5
Corn 15
Triticale 14.5
Oats 14
Wheat 12
Sorghum 10.7
Barley 10
Finger millet 6.2–7.2
Rice 3.9F 0.2
Source: Compiled from Herrera et al. (1998) and Nelson (2001).
D. Charalampopoulos et al. / International Journal of Food Microbiology 79 (2002) 131–141136
important positive therapeutic effects on coronary
heart disease, on the reductions of cholesterol and
glycemic response (Wood, 1993; Beer et al., 1995). In
addition, oat h-glucan has been reported to selectively
support the growth of lactobacilli and bifidobactera in
rat experiments (Ryhanen et al., 1996) and in in vitro
studies (Jaskari et al., 1993). High molecular weight
h-glucans, up to 3 million Da (Wood et al., 1991), are
viscous due to labile cooperative associations. Low
molecular weight h-glucans, as low as 9000 Da
(Gomez et al., 1997), can form soft gels as the chains
are easier to rearrange to maximise linkages. When
exposed to physical forces and chemical or enzymatic
hydrolysis, molecular size of h-glucan reduces to
achieve molecular weights of 0.4–2 million Da in
typical food preparations (Beer et al., 1997). Hydro-
lysates of oat h-glucan have been reported to stim-
ulate the growth of three Bifidobacterium strains and
L. rhamosus GG (Kontula et al., 1998). Among all the
cereal grains, barley and oats contain the highest level
of h-glucan, covering the ranges of 3� 11% and
3� 7% on a dry basis, respectively. It is usually
concentrated in the inner aleurone cell walls and
subaleurone endosperm cell walls of barley (Koksel,
1999), oats (Wood, 1993), and wheat (Wood, 1997).
Considerable amount of h-glucan is also found in the
crease area of wheat (Wood, 1984) and possibly other
grains. Wheat is not recognised as a source of h-glucan because of its much lower content, usually
below 1% on a dry basis. The physical properties of
wheat grain, however, allow the development of
pearling technology to separate the aleurone layer as
potential source of h-glucan. The pearling process
applies friction and abrasion to debran grains for the
improvement of milling performance. Developments
such as the PeriTec process from Satake Engineers
and the Tkac process from Tkac and Timm Enter-
prises provide the opportunity to individually collect
wheat botanical components. The combination of the
pericarp, the seed coat, and the nucellus forms a rich
source of both arabinoxylan and lignin. The bran
section in the crease area and the subaleurone section
might be separated by the subsequent milling process
and mixed into the aleurone section from debranning,
as a source of h-glucan. The successful application of
the pearling technology to other grains would rely on
factors such as proper conditioning of the grains prior
to debranning and special design of the debranner.
4.3. Oligosaccharides
Oligosaccharides, such as lactulose, fructo-oligo-
saccharides, transgalacto-oligosaccharides (Gibson et
al., 1995; Bouhnik et al., 1997) have received
increased attention, especially because they have been
shown to be effective in stimulating the growth of
bifidobacteria and lactobacilli in human large intes-
tine. These oligosaccharides can be isolated from
plant materials or can be synthesised enzymatically
(Crittenden and Playne, 1996). In the food industry,
simple oligasaccarides are used as bifidogenic sub-
stances and some infant products contain them in the
hope that this might provide some of the benefits
attributed to oligosaccharides in human milk (Rivero-
Urgell and Santamaria-Orleans, 2001). At least two
types of oligosaccarides exist in cereal grains. They
are galactosyl derivatives of sucrose, stachyose and
raffinose, and fructosyl derivatives of sucrose, fructo-
oligosaccharides (Henry and Saini, 1989). The exact
distributions of these polymers within cereal grain
have not been fully established. In respect of wheat,
reported values suggest their distributions in all mill-
ing products, including bran (Yamada et al., 1993),
germ (Pomeranz, 1988), and flour (Nakazawa et al.,
2000). Wheat germ is particularly rich in raffinose
family oligosaccharides, 7.2% on a dry basis. Total
sugar content in the aleurone cells have been approxi-
mated as 11.1% (Mizuochi, 1999) on a dry basis,
while the reported values for milling flour fall in the
range of 1.2� 1.6% (Pomeranz, 1988).
Extraction of oligosaccharides from natural resour-
ces has not been fully developed due to the complexity
of these substances and their connections with other
macromolecules, particularly proteins. Oligosacchar-
ide concentrate might be obtained from cereal botanical
constituents by exploring their water solubility. Taking
wheat as example, the water washing process com-
monly applied for gluten separationwould retain water-
soluble oligosaccharides in the starch slurry. After the
removal of starch by centrifugation or vibrating screen,
the residual paste might be centrifuged to obtain a
coloured fibrous substance, starch tailings. Oligosac-
charides can be released from other cell wall compo-
nents by the treatment of cellulase to these tailings.
Separation of oligosaccharides from both wheat germ
residue, usually after oil extraction, and from the
aleurone layer might be developed based on the sol-
D. Charalampopoulos et al. / International Journal of Food Microbiology 79 (2002) 131–141 137
ubility of oligosaccharides in 80% ethanol solution
(Henry and Saini, 1989). Purification of these materials
will require the application of cellulose column chro-
matography (Mizuochi, 1999) gel filtration (Palmacci
et al., 2001), high-performance liquid affinity chroma-
tography (Zopf et al., 1989).
Cereal bioprocessing through enzymatic reactions
or through fermentation can also produce a large range
of oligosaccharides with potential prebiotic properties.
The a-amylase present in the cereal grain can hydro-
lyse the gelatinised starch granules, and the extent of
the hydrolysis could be regulated through temperature
control. The different fractions of the oligosaccharides
obtained could then be separated and their functionality
could be tested. Another alternative for the hydrolysis
of the starch would be through fungal fermentation of
the use of solid state fermentation technology. The
processing steps prior to the starch hydrolysis (e.g.,
milling) could also have an effect in the biotransforma-
tion and should be taken into account.
4.4. Resistant starch
Resistant starch has been recognised as a functional
fibre performing an important role in digestive physi-
ology. Similar to oligosaccharides, especially fructo-
oligosaccharides, it escapes digestion and provides
fermentable carbohydrates for colonic bacteria. Resist-
ant starch has also been shown to provide benefits such
as the production of desirable metabolites including
short-chain fatty acids in the colon. In addition to its
therapeutic effects, resistant starch provides better
appearance, texture, and mouthfeel than conventional
fibres (Martinez Flores et al., 1999). Opportunities
exist for the development of ingredients from resistant
starch as prebiotics for decreasing the risk of bowel
diseases. Resistant starch might be classified into four
categories (Yue and Waring, 1998), but the natural
types are frequently destroyed when subjected to mod-
ern food processes. Resistant starch is naturally found
in cereal grains and in heated starch or starch-contain-
ing foods. The manufacture of resistant starch usually
involves partial acid hydrolysis and hydrothermal treat-
ments (Brumovsky and Thompson, 2001), heating,
retrogradation (Schmiedel et al., 2000), extrusion cook-
ing (Gebhardt et al., 2001), chemical modification
(Wolf et al., 1999), and repolymerisation (Yue and
Waring, 1998).
5. Encapsulation of probiotic strains using cereal
fractions
In the last years, several encapsulation techniques
using cereal fractions have been tested in order to
improve the viability of the probiotic strains in func-
tional foods. The possibility of using high amylose
maize (amylomaize) starch granules as a delivery
system for probiotic bacteria has been investigated
by Wang et al. (1999). In this case, Bifidobacterium
strains isolated from a healthy human were used
adhered to amylomaize starch granules. In vitro stud-
ies showed that growth in these conditions led to
enhanced survival of the probiotic strains. Survival in
vivo was also monitored by measuring the faecal level
of Bifidobacterium after oral administration of the
strain to mice. A sixfold better recovery of the strains
was noted for cells grown in amylose-containing
medium compared with the control.
A modified method using calcium alginate for the
microencapsulation of probiotic bacteria in yoghurt
has also been reported in the literature (Sultana et al.,
2000). Incorporation of maize starch (a prebiotic) with
alginate improved the encapsulation of viable bacteria
as compared to when the bacteria were encapsulated
without the starch. The survival of encapsulated
cultures was in all cases higher than with the free
cells. Techniques such as spray drying could be used
to produce small uniformly coated microspheres con-
taining the viable probiotic bacteria (O’Riordan et al.,
2001).
Other encapsulation techniques have been used by
other authors. Jankowski et al. (1997) used capsules
of a liquid starch core with calcium alginate mem-
branes, while Selmer-Olsen et al. (1999) and Shah and
Ravula (2000) used pure Ca-alginate gel beads. Adhi-
kari et al. (2000) used kappa-carrageenan for the
encapsulation of bifidobacteria in yogurt. In all these
cases, the encapsulation technique could be used to
transmit probiotic bacteria via fermented products
provided that the sensory characteristics of the prod-
uct are improved or maintained.
6. Future perspectives
Cereals are generally suitable substrates for the
growth of human-derived probiotic strains. Regardless
D. Charalampopoulos et al. / International Journal of Food Microbiology 79 (2002) 131–141138
of the relatively big differences in performance
between species and the complexity of cereal sub-
strates, a systematic approach is needed in order to
identify the intrinsic and processing factors that could
enhance the growth and, more importantly, the sur-
vival of the probiotic strain in vitro and in vivo. The
possible improvement of the organoleptic properties
should also be investigated by using supporting cul-
tures that act synergistically on the probiotic strains.
Additionally, the functionality of colonic strains
could be improved by the presence of specific non-
digestible components of the cereal matrix that could
act as prebiotics. The possibility of separating specific
fractions of nondigestible soluble fibre from different
types of cereals or cereal by-products, either through
primary processing technologies, such as pearling and
sieving, or through enzymatic modifications, looks
very promising.
The development of new functional ingredients has
the advantage that food manufacturers can add extra
value to products the consumer is already familiar
with. Developing new foods involves larger market-
ing campaigns and often the consumer needs an
adaptation time to the new product. By either devel-
oping new and innovative products or just reformulat-
ing existing ones, nutritional food ingredients enable
manufacturers to meet and exceed the expectations of
today’s health-conscious consumer. Cereals not only
have the ability to grow and deliver probiotic lactic
acid bacteria to the human gut, but also contain
potentially prebiotic compounds whose functionality
should be explored.
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