REVIEW PAPER

Possibilities to increase the quality in gluten-free breadproduction: an overview

Andreas Houben • Agnes Hochstotter •

Thomas Becker

Received: 9 November 2011 / Revised: 16 March 2012 / Accepted: 21 March 2012 / Published online: 15 June 2012

� Springer-Verlag 2012

Abstract The market for gluten-free products is

increasing. Owing to better diagnostic methods, more and

more people are identified to have coeliac diseases. Pro-

duction of bakery products that do not harm these people is

a big challenge for bakers and cereal scientists in the

twenty-first century. The use of different cereals and flours

makes it necessary to find possibilities to take over the task

of gluten by other flour ingredients, by the addition of

different components, by different flour and dough treat-

ment or by changing the method of baking. The purpose of

this review is to give an overview about the various pos-

sibilities to increase the baking quality of gluten-free

bakery products, increasing their water-binding capacity,

uniform the crumb structure and increase the final bread

volume. All the listed methods and ingredients are already

in single use helpful to increase the quality in gluten-free

bread production.

Keywords Gluten-free � Hydrocolloids � Rheology �Dough � Bread � Emulsifiers � Sourdough � Enzymes

Introduction

Baking without gluten is a big challenge for all bakers and

cereal researchers. The task of gluten to form a three-

dimensional protein network during dough preparation has

to be taken over by other ingredients in gluten-free baking.

In the recent years, owing to the increasing numbers of

people with coeliac diseases, the market for gluten-free

products has been increasing speedy. This haste is mostly

based on the improvement in the diagnosis of coeliac dis-

ease [1, 2]. The increasing market pushes the cereal

industry to increase its output of high-class gluten-free

products. To supply the market with high-quality products,

new developments and knowledge have to be aimed in

research and development [3, 4].

The absence of gluten in dough production shows high

influence on dough rheology, the production process and

the quality of the final gluten-free product. The gluten-free

doughs are much less cohesive and elastic than wheat

dough. They are highly smooth and difficult to handle; they

are more sticky, less elastic and pasty; and it is more like

handling the batter of a cake [5]. In literature, these gluten-

free doughs are often called batters instead of dough. The

doughs are not really kneaded by a lot of energy input, but

mostly mixed in mixing machines [6, 7].

The final products show some deficits in quality when

compared to French bread; their texture is crumble and

their crumbs are lighter colour [8, 9], and because of their

low carbon dioxide binding activity during raising, the

volume of the products are mostly lesser [10]. Based on the

missing interactions, the water molecules are not really

stiffly bounded in the crumb and they diffuse much faster

into the crust; this leads to a firmer crumb and softer crusts

[9]. A short shelf life, particles detection in the mouth

during consumption, a dry mouth feeling and a not really

satisfying taste are also some of the disadvantages of glu-

ten-free bread [11]. Development of new technologies and

the use of gluten-free flours, starches, hydrocolloids and

novel food ingredients will make it possible to find alter-

natives for the traditional bakery products. Especially,

changing the gas-binding capacity and the stabilization of

the starch gel during baking is the most important aspect

for being successful in reaching these aims [3]. The natural,

A. Houben (&) � A. Hochstotter � T. Becker

Lehrstuhl fur Brau- und Getranketechnologie, TU Munchen,

Weihenstephaner Steig 20, 85354 Freising, Germany

e-mail: houben@wzw.tum.de

123

Eur Food Res Technol (2012) 235:195–208

DOI 10.1007/s00217-012-1720-0

synthetic and biotechnological hydrocolloids, because of

their high water-binding capacity and their structure-cre-

ating behaviour, are mostly used in the different recipes for

replacing the gluten network and its functionality. Other

trials to replace the gluten are the use of other food proteins

like the one from soybean, eggs or milk [1]. Also the use of

enzymes can increase the gluten-free dough behaviour

required for shelf life and quality [10]. Because most of the

recipes are based on flours and starches that are by nature

poor in their nutritional level, use of different fibres,

wholemeal flour, addition of vitamins and minerals lead to

an increase in the nutritional level of the gluten-free

products [12].

Positive is also the use of a very traditional bakery

ingredient, of sourdough, because of it textural and sen-

sorial advantages [13]. All these treatments and ingredients

allow making gluten-free bakery products better in quality.

The aim of all these changes is to reach a final product

close to French bread quality [1].

Gluten-free flours and starches

Most non-gluten-free bakery products are based on wheat,

rye, barley or even oats. Among these, oats should be

gluten-free by nature but due to its planting and breeding

procedure, in literature it is often counted as the non-glu-

ten-free grains. So all these grains and flours are forbidden

in the gluten-free bread production. Only gluten-free

cereals and the so-called pseudocereals are allowed to be

taken as raw materials.

Gluten-free cereals are, for example, rice, maize and

millet. Up to now, two different rice species—Oryza sati-

va, originating from Asia, and Oryza glaberrima, culti-

vated in Africa [14]—and different subspecies of zea mays,

millet species and Sorghum bicolor L. Moench [15], teff

(Eragrostis tef (Zuccagni) Trotter), finger millet (Eleucine

coracana L. Gaertn.), pearl millet (Pennisetum glaucum

(L.) R. Br.) and foxtail millet (Setaria italica (L.)

P. Beauv.), are used in the production of gluten-free bakery

products [16]. Next to these grains and grasses, the

pseudocereals amaranth, buckwheat and quinoa are often

taken for gluten-free bakery products. The pseudocereals

do not belong to the monocots, like the cereals do, but

belong to the dicots. Some species used in human nutrition

are buckwheat (Fagopyrum esculentum Moench), tartary

buckwheat (Fagopyrum tataricum Gaertner), some ama-

ranth spp. like Amaranthus caudatus L., Amaranthus

cruentus L. and Amaranthus hypochondriacus and Che-

nopodium quinoa [17].

Next to gluten, pseudocereals are mainly taken as an

ingredient in gluten-free products because of their nutri-

tional level, high protein value, essential amino acids and

fatty acids and high mineral content [18]. The functionality

of the flours made from these grains and pseudocereals

depends on their particle size, the particle distribution, the

milling yield and the flour treatment. Also the growing

conditions and the plant species influence the composition

of the ingredients and by this the final product quality

[17, 18].

Next to gluten-free grains and pseudocereals, flours

made from legumes like chickpea, field bean, soya bean

and French bean, from cassava [18–20], chestnut, coconut,

linseed and from plantain are also used as starch additives

because of their water-binding capacity in the recipes of

gluten-free bakery products.

There is mostly a mixture of different gluten-free flours

and starches. Especially, the starches, the most important

stored carbohydrates in plants, have a high influence on the

dough parameters, the texture, the moisture retention and

the final quality [21].

The role of starch during baking is to bind the water and

create a gas-permeable structure [22]. Commercial gluten-

free starches are mostly obtained from rice, cassava,

potatoes and maize [1, 7, 20, 23]. Since 2008, there is also

a gluten-free wheat starch available on the market, whose

gluten content is beyond 20 mg kg-1, the borderline given

by the codex alimentarius; it does not harm most coeliac

patients [24].

The differences between the listed starches in their

thermal behaviour, gelatinization process, gel-forming

behaviour and final texture are based on individual com-

position and chemical structures [21]. Its functionality is

mostly influenced by its main components, the glucose

polymers amylose (linear, 1–4 glycolysed a-D-glucose

units) and amylopectin (complex bounded 1–4 and 1–6

glycolysed a-D-glucose units). These components are

associated with hydrogen binding into crystal and form an

insoluble kernel shape in cold water. By reaching a high

temperature during baking, the starch kernels irreversibly

swell by the uptake of water. The needed temperature, the

so-called gelatinization temperature, is a characteristic

parameter for every starch. The intermolecular hydrogen

bonds are broken up, and the hydroxyl groups released are

immediately hydrated. The special relation of the hydroxyl

groups of water is the basis of gelatinization. A further

increase in temperature leads to higher molecular activity

and by this to partial softening of the intermicellar network.

Some parts of the amylose molecules are colloidal dis-

solved, and the increase in hydration finally creates a paste

similar to starch mixture. The starches form a composite

gel network, consisting of swollen amylopectin, filling an

interpenetrating amylose gel matrix [25]. 21, 26By lower-

ing temperature and molecule activity, the starch paste

confirms again [21, 26]. The swelling behaviour, the

maximum water-binding capacity and the needed

196 Eur Food Res Technol (2012) 235:195–208

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gelatinization temperature of the starch are influenced by its

origin, the species, its combination, the concentration and its

particle size, the amylose/amylopectin ratio, the starch treat-

ment, the moisture content, the pH value of the water and other

molecules in the mixture (e.g., sugar, fat, proteins, salt) and

hence, the rheological behaviour of the dough and also the final

bread crumb structure [21, 26–29]. Also the starch granule

shape, its molecular weight and particle size distribution are

responsible for the process of gelatinization [30]. A higher

degree of crystallinity results in requiring a higher gelatiniza-

tion temperature of the starch [31]. From nature, the amylose/

amylopectin ratio differs a lot; the amylose content is inversely

proportional to the gelatinization temperature [31, 32]. All for

gluten-free production used starches show to have a shear

thinning behaviour (pseudo plastic) [33]. The biggest influence

of the natural origin of starch is shown during the baking

process and in the dough density. In baking, the highest dough

density is reached by the use of wheat starch; all other starches

create doughs with more air included [25, 33–35]. Also the

highest bread volume is reached by the use of wheat starch,

while creating the dough with the lowest flow index and hence

with the best gas-expanding possibility [33, 36]. Higher starch

gelatinization temperatures lead to higher final bread volume,

because the change from batter and dough, as a fluid, aerated

emulsion to a solid, porous structure, takes place later and

allows increasing the volume for a longer time [37–39]. The

most similar in behaviour to gluten-free wheat starch is the rice

starch [33]. But if the gelatinization, because of a very high

gelatinization temperature, is not totally finished, the volume

is decreased after cooling down [26]. The addition of other

ingredients like shortenings, eggs or proteins to the dough

influences the gelatinization temperature as well [25, 33].

Next to the native starches, modified starches are used in

the food industry. They are made out of native starches by

chemical, enzymatical, mechanical and/or thermal treat-

ment and can be used for reaching specified aims in the

textural of bread baking [29, 40].

In gluten-free bread production, the most used modified

starches are the cross-linked ones like distarch phosphate

and distarch adipate, starch esters like monostarch phos-

phate and starch acetate, partial complex bounded or pre-

gelatinized starches and mechanical treated or extruded

starches. These modified starches are able to change the

dispensability, the water absorption, the swelling behav-

iour, the gelatinization temperature and the viscosity of the

dough. They are used as a thickening agent; they stabilize

the crumb structure and can decrease retrogradation [27].

Hydrocolloids and gums

In gluten-free baking, hydrocolloids can also be used as a

gluten replacer because of their character to stabilize the

products and increase their texture. Their chemical struc-

ture makes them mostly belonging to the polysaccharides.

They are often used as a thickening agent, helping in

swelling, for stabilization, for gelatinization and as a

humectant agent. In the gluten-free baking, hydrocolloids

used can be classified into the one from plant origin and the

chemical synthetic created ones. The plant origins can be

(a) from marine algae like agar–agar and carrageen,

(b) plant extracted like pectin and oat b-glucan, (c) plant

exudate like gum arabic and tragacanth, (d) seed mucilage

like locust bean gum, guar gum and psyllium, (e) starches

and modified starches and other natural hydrocolloids like

konjak. Next to these hydrocolloids, the chemically or

biochemically synthesized cellulose derivatives such as

hydroxypropyl methylcellulose (HPMC), carboxymethyl-

cellulose (CMC) and methylcellulose (MC) and microbial

biosynthetic hydrocolloids such as xanthan and proteins—

casein, soy protein and egg albumin—are also used [41–

43].

Polysaccharide hydrocolloids are formed by glycosidic-

bounded monosaccharide molecules in a linear and/or

cross-linked structure [27]. In gluten-free dough prepara-

tion, they are often used for creating the viscoelastic and

cohesive behaviour of gluten [44] and to increase the gas-

binding capacity by raising the viscosity [45, 46]. They

also interact with the swelling, the gelatinization and gel-

ling properties of the dough and the retrogradation of the

starch [47]. In dough, all hydrocolloids work together with

the water molecules included in dough; they reduce their

diffusion and support the stability of the system. Xanthan

gum, guar gum and CMC are soluble in cold water; indeed,

the hydrocolloids carrageenan, locust bean gum and most

alginates need hot water for their full hydration. The water

molecules are bound to the hydrocolloids in three different

ways: via hydrogen bounds, embedded in inter- or intra-

molecular openings or immobilized by structuring [48].

The hydrocolloids with a branched, tangled ball-shaped, or

chained structure are taken as thickening agents (hydration

of the macromolecule); indeed, hydrocolloids with a

thread-like, linear structure are taken as gel-forming

agents. The gel-forming process of hydrocolloids is real-

ized by connecting the fibril polymer molecules or polymer

molecule bunches, which are intermolecularly fixed to each

other by hydrogen bonds or by cross-linking of anionic

molecules by multivalent cations (calcium ions or pro-

teins). A three-dimensional network is by further linking of

these limited ordered structures formed out; the resulting

cavities have a defined water-holding capacity. When there

are regular and irregular sequence segments and the inter-

chain interaction of the sequence segments with normal

conformation is interrupted by irregular sequences in the

chain, gel forming is possible. In contrast to the gluten

network, where both fibril and film formations occur, the

Eur Food Res Technol (2012) 235:195–208 197

123

hydrocolloid networks show only to have a fibrillar char-

acter. The dominant type of bounding is also different.

Hydrogen bonds, cationic cross-links and hydrophobic

interactions are common in hydrocolloid networks; in the

gluten networks, there are mostly covalent disulphide

bonds, electrostatic, van der Waals and dipole–dipole

interactions, hydrogen bonding and hydrophobic associa-

tions. Because the sulfhydryl groups in hydrocolloids are

absent in gel formation, the presence of reducing agents

and oxidation agents is not necessary. In gluten-free bak-

ing, hydrocolloids are often used singly or in combination,

always based on their technological effect on dough and

the final product [27, 42, 49–51].

However, there exist specific characteristics and effects,

for example, cold and hot solubility, of each hydrocolloid

for all kind of doughs. For example, xanthan (linear,

anionic and substituted polymer) is able to create, over a

huge temperature range, a constant high viscosity and

finally forms a weak, cold-set gel out [52–55].

The modified cellulose derivative HPMC (linear and

neutral polymer) has, because of its hydrophilic character,

a high water-binding capacity and also has, in its structure,

hydrophobic methyl and hydrophilic hydroxypropyl groups

located, which makes HPMC an interface activity in the

dough system during the resting period (promoting dis-

persion/preventing coalescence of the gas bubbles). The

molecular structure of HPMC is shown in Fig. 1; its foam

forming is shown in Fig. 2 [56, 57].

HPMC can create a reversible, heat-set gel network

[56, 57] that leads to an increase in dough viscosity and

stabilization of the boundaries of the expanding gas cells.

During baking, the gas-binding capacity is increased and

higher volume can be, as shown in Fig. 3, reached in the

final bread [43].

The influence of the hydrocolloid on the dough rheology

and the bread quality, especially the final volume and the

crumb texture, depends on the specific options of the

hydrocolloid used, like molecular mass, molecular struc-

ture, chain length and bonds and chemical modification;

the added amount; the flour and starch raw material used;

other recipe ingredients; and the process parameters used

like pH value, temperature, shearing, ionic bonds and the

attendance of ions [21, 61–63]. The results by the addition

of a hydrocolloid are based on the increase in stiffness due

to a decline in the starch swelling and the decrease in

dissolved amylose. By inhibiting the inter-particle inter-

actions of the swollen starch granules, the hydrocolloid

softens the starch network [63].

The functionality of the different hydrocolloids in the

system dough is created and influenced by the interactions

with the other added food polymers, like starch and pro-

teins. It is well known that these ingredients influence each

other and the final bread quality, but up to now, there is less

knowledge about the mechanism of these interactions [21].

Proteins

To form a network similar to what gluten does in bread

production, proteins can also be added during dough

preparation [7, 64, 65]. The proteins used can be like milk

proteins and egg albumins from animal origin or like the

proteins of soya, taken from plants.

Milk proteins have a high nutritional level and are quite

often used because their chemical structure is quite similar

to the one of gluten proteins [66]. They pretend to swell in

a high level, and they are also able to build up a network

[47, 64]. In Fig. 4, the addition of milk protein to a gluten-

free flour mixture is shown in comparison to a French

bread with a three-dimensional gluten network and a

commercial gluten-free mixture.

Depending on the kind of milk protein, a specific change

of the product quality can be reached. Caseinate is a good

emulsifier and is able to stabilize a batter; isolated and

concentrated whey proteins can form gels, and high tem-

perature skim milk powders have a high water-binding

capacity [67]. The functionality of the quite heat-stable

hydrophobic caseinate molecules is linked to their aggre-

gated status as caseinate complex or caseinate micelles.

Because of their flexibility, there is nearly no cysteine and

cysteine, open and on the environment-based conforma-

tion, the monomers are different from other milk proteins.

The micelles are not stiff pressed, but they are very porous,

and so, they are dissolved in water. The main whey

Fig. 1 Molecular structure of

HPMC (b-(1-4)-glycosidic

bounded glucose units, partial

substituted by methyl or

hydroxypropyl groups [58]

198 Eur Food Res Technol (2012) 235:195–208

123

Fig. 2 Foam-forming behaviour of HPMC (left, q = 0.62 g/cm3) and xanthan gum (right, q = 0.83 g/cm3) in a level of 2 % added to water;

scale bar 5 mm [59]

Fig. 3 Yeasted bread made from wheat starch without the addition of

hydrocolloids (reached total volume 1650 ml; received volume out of

1 g flour: 3,9 cm3) left hand side; yeasted bread made from wheat

starch and addition of 2 % xanthan (2000 ml, 3,5 cm3) middle;

yeasted bread made from wheat starch and addition of 2 % HPMC

(2490 ml, 5,3 cm3) right hand side (original procedure of Jongh)

[3, 60]

Fig. 4 Comparison of different bread types. On the top, the surface

and a typical slice view; beyond the demonstration of pictures

received in CLSM (benchmark scale 50 lm); wheat bread sample (a);

gluten-free bread from a commercial gluten-free flour mix (b); gluten-

free bread sample without the addition of milk protein (c); gluten-free

bread with added milk protein (d) [7]

Eur Food Res Technol (2012) 235:195–208 199

123

proteins, the a-lactalbumin (four disulphide bonds) and the

b-lactoglobulin (one free thiol group and two disulphide

bonds), which can be a monomer, dimer and an oligomer

depending on pH value, ionic strength and temperature,

have a globular structure and hydrophobic, compact folded

polypeptide chain. The heath sensitivity of the b-lacto-

globulin can be used via temperature treatment for partial

up-folding and aggregation of the whey proteins by thiol

disulphide interactions and hydrophobic bonding. The

resulting porous structures absorb and immobilize the water,

increase the water uptake, give stability to the dough and the

final product, and elongate shelf life [27, 47, 68, 69].

Next to its functional benefit, the addition of milk pro-

teins and essential amino acids like lysine, methionine and

tryptophan also increases the nutritional level of the gluten-

free bakery products [70]. During dough production, the

addition of dairy-based ingredients increases the water-

binding capacity, lowers the dough stickiness and makes

dough behave more plastic [1]; in the final bread, it

increases the volume and improves the texture, taste, crust

colour and the shelf life [70–74]. The addition of high-

protein and poor lactose milk-protein ingredients shows a

clear quality increase [64]. The colouring of the crust is

based on different maillard and caramelization reactions

supported by milk products including lactose [64, 67]. But

there are also some disadvantages in the use of milk pro-

teins. First, for people with small intestine inflammation

because of coeliac disease, there is often a link also to

lactose intolerance. These people cannot metabolize the

lactose because of a secondary lactose intolerance, when

the enzyme lactase, which is normally located in the small

intestine mucosa, is nearly absent because of the villous

atrophy [75].

The second reason is that milk proteins can also be the

activator of an allergenic reaction. And in low-protein

diets, bakery products with a low allergenic potential are

taken [3]. Because of their composition and their way of

production in the market, existing milky ingredients for the

bakeries have different functionality [70, 73].

Next to milk proteins, the proteins of surimi, soya beans

and egg proteins can also be used for the addition of protein

in gluten-free bakery products [1]. Surimi has a high

functionality and shows a good gel-forming behaviour

[76], so it is used to replace protein in gluten-free baking

[77]. Its creation of stiff, cohesive gels is linked to the high

content of highly elastic actomyosin and myosin com-

plexes or myosin molecules [78–80]. The thermo-irre-

versible hydrogels are created by the thermal denaturation

and dissociation of, for example, the actomyosin com-

plexes, and reforming of intermolecular hydrophobic and

covalent bonds. The water molecules are immobilized by

clathration [81]. The dissociation of actomyosin and

myosin complexes is supported by the addition of salt and

increases the cohesive and elastic texture of the gel [82].

The use of four different surimi preparations was tested in a

gluten-free recipe, based on rice and potato starch [77].

Three of these surimi products were able, in comparison

with a standard recipe, to enhance the crust colour, create a

softer crumb and reach a higher bread volume. Only one

sample was able to enhance the taste of the bread. Besides

all the positive effects detailed so far, it is up to now not

known whether the customer will accept the fish taste

proteins in gluten-free bakery products [3]. And, next to the

milk proteins, the fish, the soya and the egg proteins can

also be responsible for allergenic reactions. Also these

ingredients cannot be allowed in bakery products for a low-

protein diet [3].

Soya protein, also high in its essential amino acid lysine

content, can be added in the form of high-protein soya flour

or as a soya protein isolate and can lead to an increase in

crumb texture and bread volume [20, 83, 84].

Legume proteins show strong gel-forming behaviour

and can be used for the production of emulsions and foams.

Their functionality depends on the environmental param-

eters like pH value, ionic strength and temperature. The

soya proteins are divided into the two heterogeneous

groups, globulin (90 % of the total amount) and albumin

(10 %). The polymeric main components of the globulin

fraction, the 7S and 11S globulins, are formed by 3 or 6

subunits, which are glycolysed or have one disulphide bond

[27]. In the amino acid composition of soya globulin, there

is a high content of asparagine, aspartic acid, glutamic acid

or glutamine. Stabilization of the subunits and the overall

structure is reached by hydrophobic interactions. By ther-

mal treatment, the intramolecular interactions are stopped

and intermolecular interactions and aggregation via

hydrogen and ionic bonds start [85].

As a gluten replacer, egg proteins can also be used. Due

to their border areas activity, they are considered for bak-

ing as a foaming agent, as a crumb stabilizer and for cre-

ating a good shape. Especially, the heat coagulation of the

protein and the egg yolk contained phospholipids and

lipoproteins as emulsifiers facilitate the dispersion and

stabilization of gas bubbles in the gluten-free dough sys-

tems [3, 86]. The swelling of the egg proteins in gluten-free

dough lead to a viscous fluid that shows a similar network

protein structure function than the one known from gluten

[7, 87]. During the addition of egg white build-up, thermo-

reversible protein gels are based on hydrophobic interac-

tions. Except the nine thermostable disulphide bonds

including ovomucin, all other egg white proteins are

responsible for the gel-forming process [83]. These phe-

nomena form the protein structure and are able to give

stability to the dough.

Other sulphur containing egg white proteins, especially

the main egg white protein, ovalbumin (54 %), which

200 Eur Food Res Technol (2012) 235:195–208

123

includes four thiol and one disulphide group, stabilize the

gel by polymerization via the thiol disulphide exchange.

Also the coagulation of the egg yolk during thermal

treatment creates similar thermo-irreversible gels. In the

baking industry, the egg yolk is often used as an emulsi-

fying agent [27, 88]. An increase in the bread volume and

the amount of pores per square centimetre because of the

addition of full egg powder was shown by Moore [89].

Figure 5 shows that the positive effect of an addition of egg

powder can be increased further by the additional use of the

enzyme TG; here a layer-like protein structure is received

by covalent isopeptide bonds.

Jonagh et. al. [90] showed that egg albumin can increase the

gas-binding capacity by connecting the starch granules. In

comparison with the other protein sources, the best crumb

texture of gluten-free bread was reached by the addition of full

egg powder [89]. By the addition of already foamed egg, it was

possible to increase the gas binding during dough preparation

and stabilize the bread structure [91].

The ovalbumin inside the egg white denatures and

aggregates during pitching because of the increase in the

interface of liquid and air. Stable gas foam is created,

which looses the dough and stabilizes the dispensation of

further ingredients. The egg white protein ovomucin sta-

bilizes the gas bubbles by forming fibrillar structures, and

is very effective. During baking, the protein network

coagulates and prevents the coincidence of the bread [27].

Next to this, the protein network is able to reduce the

swelling and gel forming of the starch.

Enzymes

A lot of enzymes are naturally included in the raw mate-

rials, like in most flours. But not to influence negatively the

final product quality by destroying the crumb structure or

decreasing the volume, they are mostly inactivated during

the various production steps [47]. In gluten-free and also in

gluten-contending recipes, enzymes are very often added to

improve the dough-handling properties and to increase the

final baking quality. Depending on the enzyme activity, the

water-binding capacity, the shelf life, the retrogradation

and the crumb softness can be influenced positively [10].

Some of those enzymes that are often used in gluten-free

bread production are the starch-modifying amylase,

cyclodextrin glycosyltransferases (CGTase, EC. 2.4.1.19)

or the protein-connecting transglutaminase (TG, EC.

2.3.2.13). Also glucose oxidase (GO, EC. 1.1.3.4), laccase

(EC. 1.10.3.2) and proteases can be found in the recipes

[10, 89, 92–95]. Some of these enzymes are essential for

reaching higher quality in gluten-free bread.

In protein cross-linking, one of the reactions catalysed

by the enzyme transglutaminase (TG) is the important

trans-acylation reaction between, as an acyl donor, the

c-carboxamide group of a protein- or peptide-bound glu-

tamine and primary amino acyl-acceptor. Inter- or intra-

molecular covalent isopeptide bonds are formed if this

acceptor is a e-amino group of a lysine residue [94, 96, 97].

In Fig. 6, the differences by TG catalysed reactions are

shown.

The transglutaminase used in baking is always from

microbiological origin. The enzyme shows different

activity depending on the accessibility of glutamine and

lysyl residues in the proteins [99, 100]. A high TG activity

can be expected by the composition of the caseinate and

soya proteins, but also of some fractions of the egg, wheat,

meat and whey proteins [97, 101]. It is possible to create,

by the addition of transglutaminase, a network in high-

protein-content, gluten-free baking products whose stabil-

ity depends on the protein origin, its thermal compatibility

Fig. 5 CLSM pictures of gluten-free bread crumb; addition of egg

powder (a), addition of egg powder and 1 U TG per gram protein (b);

A denser and more branched network is formed out by the addition of

TG; the crumb was coloured with safranin, size was 63 times

magnified, size scale is 50 lm [89]

Eur Food Res Technol (2012) 235:195–208 201

123

[102] and the dosage of the enzyme. The addition of skim

milk powder, an egg protein powder, forms with protein

networks and increases the stiffness and the sappiness of

the crumb. A lower baking loss can additionally be

reached.

In combination with skim milk powder, a higher addi-

tion of TG leads to a high increase in crumb firmness but

also to an increase in the amount of pores per square

centimetre. In rice flour-based bread, the addition of TG

leads to cross-linking [103]. In Fig. 7, an example for

increasing baking quality by the addition of TG is shown

[104]. In this study, it was worked out that special buck-

wheat and brown rice flour pretend to be good TG sub-

strates, whereas sorghum, teff and oat flour did not work

out that good. Buckwheat and rice naturally include high

amounts of glutamine and lysine [84]. The doughs based on

maize flour increase their baking quality by TG addition

not by protein cross-linking but by deamination of the

glutamine residues.

The enzyme GO received from fungus catalyses the

oxidation of b-D-glucose to D-gluconolactone or D-glucon

acid and hydrogen peroxide. The hard oxidizing agent

hydrogen peroxide interacts as well with the very reactive

thiol groups of the proteins by forming disulphide bonds

[10]; moreover, it creates the cross-linking of the water-

insoluble pentosans via oxidation of the ferula acid [105]

and creation of other non-disulphide bonds like dityrosine

and dehydroferulic acid-protein bonds [103, 105, 106]. The

enzyme laccase catalyses by a similar effect the oxidation

of phenolic substances under reduction of oxygen. By

cross-linking proteins and proteins with arabinoxylans,

laccase is able to stabilize the dough structure [107]. The

cleavage of the a-1, 4 glycosidic bonds and the sometimes

Fig. 6 TG catalysed reactions. a acyl group transfer between the

c- carboxamide group of a protein or peptide bound Gln residue and a

primary amine; b cross-linking between protein bound Gln and Lys

residues to form a e-(c-glutamic)-lysine isopeptide bond; c deamina-

tion of the Gln residue by water [98]

Fig. 7 Some slices of gluten-free bread based on buckwheat flour (BW), brown rice flour (BR) and maize flour (CR) after addition of different

levels of the enzyme transglutaminase; 0, 0.1 and 10 U TG per gram protein [104]

202 Eur Food Res Technol (2012) 235:195–208

123

simultaneous cyclization of the resulting fragments inside

the starch molecules is catalysed be the enzyme CGTase

[108]. These cyclodextrins give, by the formation of

inclusion complexes with lipids or hydrophobic proteins,

emulsifying properties to the dough and can lead to an

increase in the crumb structure and a better gas binding in

gluten-free rice bread and finally aim in a higher specific

volume [93]. Also staling of gluten-free bread because of

the cyclodextrins reportedly decreased, based on interac-

tion with retrogradation of the amylopectin and other

interactions between proteins and starch [109].

In the past, most enzymes were sold immobilized on wheat

flour or wheat starch as carrier, but this phenomenon no longer

exists [10]. For using combinations of different enzymes in

gluten-free baking, presence of any antagonistic effects must

be checked first. The existence of the needed enzymes for

gluten-free products is the only limiting factor.

The use of sourdough

Sourdough fermentation is one of the most used and most

effective way of increasing flavour, taste, shelf life and the

structure of all kinds of bread [110–112]. Next to traditional

use in rye- and wheat-based bread production, it is also

widespread in gluten-free bread production [13, 110, 113]. It

has already been proved [13] that small amounts of lactic acid

bacteria-fermented sourdough in gluten-free dough produc-

tion, in comparison with chemical acidified and non-acidified

dough, can increase the viscosity, homogenize the crumb

structure, elongate the shelf life and create a stronger flavour

[13, 114, 115]. There is no substrate and activity limitation for

the lactic acid bacteria in gluten-free flours, but its fermen-

tation can differ between the strains used. There is always a

need for a compatibility test of substrate and starter strain

[113, 116–119] [114]. Next to the changes in bread quality,

the microbiological stability of gluten-free bread is also

increased by the use of sourdough [120]. The production of

antifungal organic acids (lactic acid, phenyl lactic) and cyclic

dipeptides (cyclo (L-Leu-L-Pro), cyclo (L-Phe-L-Pro)) can

delay the spoilage of bread [13]. During fermentation build-

up, organic acids and free amino acids, depending on the

selected starter culture, are responsible for the increase in

taste by the use of sourdough [121]. Next to the already listed

benefits of the use of sourdough in gluten-free bread pro-

duction, there can also be a helpful enzyme and exopoly-

saccharide production in the selected lactic acid bacteria.

During the fermentation of sucrose or raffinose, exopolysac-

charides and oligosaccharides are formed and lead to an

increase in the water-binding capacity. This optimizes the

starch gelatinization, slows staling and improves shelf life of

gluten-free bread [122–124]. The homopolysaccharides are

important in sourdough. The most common ones are dextran

and levan; glucan and fructan polymers that are built from

glucose and fructose units, and the synthesis is catalysed by

extracellular glucosyltransferases. Some of the homopoly-

saccharides (e.g., levan of L. sanfranciscensis) show a pre-

biotic effect and support the bifidobacteria in the intestine

[125]. The positive effect of sourdough addition on bread

volume and crumb structure is shown in Fig. 8 [126]. Next to

the use of sourdough, the use of chemical acids can also have

positive effects in gluten-free bread production [127].

Fat, oil and emulsifiers

The stabilization of the gas bubbles in bread dough is often

reached by the addition of fat. During kneading, the fat crys-

tals adsorb at the gas bubbles interface inside the dough, and

during baking, they melt and give the gas bubbles the

Fig. 8 Slice from gluten-free sorghum bread, the used flour was a mixture of 70 % sorghum and 30 % potato flour and an addition of 2 %

HPMC; a no use of sourdough b use of 70 % sorghum sourdough [126]

Eur Food Res Technol (2012) 235:195–208 203

123

possibility to expand without destruction [128, 129]. Next to a

decrease of the starch gelatinization and the starch solubility in

gluten-free bread production, the addition of margarine leads

to an increase in the gas-binding capacity [91]. By the addition

of vegetable oil, the kneading resistance is decreased and also

the swelling of the starch granules is reduced by complexation

of amylose with the monoacyl lipids [93]. The vegetable oil

results in a softer crumb and an increase in the specific volume

too [93]. An additional increase in the dough stickiness was

reported by Schober et al. [130].

Emulsifiers can be used to increase the dough stiffness,

improve the bread structure and decrease the speed of

staling. Due to their amphiphilic nature and their ability to

migrate to interfaces, they can reduce surface tension and

produce stable dispersions for the crumb [131]. By inter-

action with the starch molecules, they retard retrogradation

and inhibit the migration by immobilization of the water

[132]. They increase the gas absorption of the dough by

reducing the gas bubble surface tension [133]. Defloor

et al. [19] showed that an increase in the bread volume, a

change of the dough viscosity and a decrease in drying-out

process of the crumb are reachable by the use of glycerol

monostearate. By the addition of emulsifiers and fat, it

should always be kept in mind that overdosage cannot lead

to a total loss of crumb structure. Not only the right

emulsifier and fat but also the right dosage is important [3].

Conclusion and outview

The various listed-up methods show that not just one single

ingredient in gluten-free bread production can replace the

gluten and its functionality. The use of one enzyme, of one

additional starch, natural or modified, of just sourdough or

the addition of just one hydrocolloid can already increase

dough and bread quality. But a costumer-satisfying struc-

ture, a high volume and a good taste can only be reached by

a composition of replacers. The complexity of these addi-

tives shows the big challenge of cereal technology in the

twenty-first century. The next step is to work out the

interactions of these functional additives with the basic

ingredients. Not all functional additives show the same

activity and the same result for all starches and flours, so

there are no general statements possible.

A great benefit can be further use of sourdough. It

increases enzymatic activity and gives next to functional

benefit also an additional aroma to the product and elon-

gates shelf life. Great use in dough handling and crumb

softness can be expected by the addition of protein-con-

necting and also starch-crashing enzymes in the right

dosage.

Next to changes in the recipe, changes in dough prep-

aration and the use of dough pretreatment forecast to be a

good way in gluten-free bread production. A lot of work is

already done in the last years in high-pressure (HP) treat-

ment for polymer gluten-free ingredients. High-pressure

treatment is a non-thermal step to modify or even dena-

turize the proteins and change the properties of carbohy-

drates and fats [134]. There is a decrease in the quality of

oat bread made by high-pressure treatment above 350 MPa

[135]. This HP works out covalent bondages in the protein

network and leads to a gelatinization of the starch; finally,

it comes to an increase in dough stiffness and elasticity.

The final bread is smaller in size, and its crumb is harder

Fig. 9 First line oat dough samples with different pressure treat-

ments; on the left side the control without any special treatment; in

the other doughs 20 % of hp treated dough is added (200/350/

500 MPa); in the second line bread samples of the final oat bread.

Left side, bread made out of the dough without treatment, the other

breads are made by the addition of 10 % hp treated dough to the basic

recipe (200/350/500 MPa) [135]

204 Eur Food Res Technol (2012) 235:195–208

123

than without HP (Fig. 9). Smaller pressure levels weaken

the protein network by dissociation and weakening

hydrophobic and electrostatic bondages. The reallocation

of water and changes in the protein starch interactions

finally lead to homogeneous crumb pores. The addition of

10 per cent hp (200 MPa) oat dough to the basic dough

leads to an increase in the volume and a retardation in

staling of the final bread [135, 136].

For the hp treatment, next to the right pressure level, it is

necessary to find the optimal ratio between increase in

bread quality and decrease in staling.

The development in gluten-free baking products still

goes on. Further investigations and research are necessary

to increase quality and offer coeliac disease patients high-

quality baking products. With an increase in the request

for gluten-free baking products by non-coeliac disease

patients, the speed of developments will raise and the

prices for the final products on the market will go down.

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