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gluten-free bread characteristics
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Crust and crumb characteristics of gluten free breads
E. Gallagher a,*, T.R. Gormley a, E.K. Arendt b
a Teagasc, The National Food Centre, Dunsinea Castleknock, Dublin 15, Irelandb Department of Food Science Technology and Nutrition, National University of Ireland, Cork, Ireland
Received 21 October 2001
Abstract
Gluten free breads often have poor crust and crumb characteristics and the current study was conducted to help alleviate this
problem. A commercial wheat starch (Codex Alimentarius) gluten free flour was supplemented with seven dairy powders (0%, 3%,
6%, 9% inclusion rates based on flour weight). Initially a fixed water level was used (trial 1) and the resulting batters were proofed
and baked. The breads were tested 24 h after baking. Powder addition reduced loaf volume by circa 6% (P < 0:001). Increasing theinclusion levels of the powders decreased loaf volume (P < 0:001) with a decrease of 8% for the highest level. Powder addition
generally decreased the crumb L�=b� (white/yellow) ratio. Crust L� values were significantly reduced. All of the powders increased
crumb hardness (P < 0:001) with the exception of demineralised whey powder. Ten and 20% additional water (trial 2) was added tothe formulation and the resulting breads had higher volume, and a much softer crust and crumb texture. Sensory analysis revealed a
preference for breads containing skim milk replacer, sodium caseinate and milk protein isolate.
� 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Gluten free; Bread; Dairy powder
1. Introduction
Coeliac disease affects the small intestine and is due to
a sensitivity to gluten (Anonymous, 1982). An accept-
able treatment is strict adherence to a 100% gluten-freediet for life. This can prevent almost all complications
caused by the disease.
Gluten is the main structure-forming protein in flour,
responsible for the elastic and extensible properties nee-
ded to produce good quality bread. To ensure the ac-
ceptability of gluten free bread, the loaves must have
quality characteristics similar to those of wheat flour
bread. (Paulus, 1986; Ylimaki, Hawrysh, Hardin, &Thomson, 1991). Currently, many gluten free breads
available on the market are of a low quality, exhibiting a
dry crumbling crumb, resulting in poor mouthfeel and a
poor flavour (Gallagher & Gormley, 2002). Conse-
quently, trial 1 in the current study was conducted to
alleviate this problem. However, the removal of gluten
from bakery products negates bread quality and so the
use of polymeric substances that mimic the viscoelas-
tic properties of gluten is often required, (Christianson &
Gardner, 1974; Kent & Evers, 1994; Toufeili et al., 1994).
The incorporation of dairy ingredients has long beenestablished in the baking industry (Stahel, 1983; Zadow
& Hardham, 1981). Dairy proteins are highly functional
ingredients and due to their versatility can be readily
incorporated into many food products. They may be
used in bread for both nutritional and functional bene-
fits including flavour and texture enhancement, and stor-
age improvement (Cocup & Sanderson, 1987; Kenny,
Wehrle, Auty, & Arendt, 2001; Mannie & Asp, 1989).Dairy products may be used in gluten free bread for-
mulas to increase water absorption and, therefore, en-
hance the handling properties of the batter.
In a second trial, the effects of adding different levels
of water on the volume, crumb and crust characteristics
of the breads was investigated. In their studies, Platt and
Powers (1940) found a strong correlation between the
staling rate of bread and moisture content. Also Bechteland Meisner (1954) concluded that bread with a higher
moisture content was significantly fresher than bread
with a lower content.
Journal of Food Engineering 56 (2003) 153–161
www.elsevier.com/locate/jfoodeng
*Corresponding author. Tel.: +353-1-805-9500; fax: +353-1-805-
9550.
E-mail address: [email protected] (E. Gallagher).
0260-8774/02/$ - see front matter � 2002 Elsevier Science Ltd. All rights reserved.
PII: S0260-8774 (02 )00244-3
The aim of the current study was to incorporate arange of dairy powders into a gluten free bread formu-
lation; to investigate their effects on the baking charac-
teristics, crumb properties and protein and dietary fibre
contents of the breads; and also to study the effects of
increasing the moisture content on the crust and crumb
characteristics of the gluten free breads. Little work has
been published in the area of gluten free breads (�AAcs,Kovacs, & Matuz, 1996) and for this reason the datafrom the current study are often compared with results
from studies involving wheat breads.
2. Materials and methods
2.1. Materials
The control gluten free formulation contained com-
mercial wheat starch (Codex Alimentarius) gluten free
flour (Odlum Group, Dublin, Ireland), fresh yeast
(Yeast Products, Dublin, Ireland), vegetable oil (CrestFoods Ltd., Dublin, Ireland) and DATEM (Quest in-
gredients, Holland). In the trials this was supplemented
with dairy powders obtained from Kerry Ingredients
(Listowel, Co. Kerry, Ireland). The names (the abbre-
viated names are used in the following text) and protein
content of the powders are given in Table 1.
The batter recipe (based on flour weight) was 100%
gluten free flour, 87% water 35 �C, 2.7% fresh yeast, 1%oil and 0.5% DATEM. In trial 1, the dairy powders were
added at 3%, 6% and 9% of flour weight. In trial 2, 10%
and 20% additional moisture was added to breads con-
taining 6% inclusions of molkin (mlk), kerrylac (klc) and
milk protein isolate (mpi). Breads for both trials were
prepared by blending the liquid ingredients together.
These were then added to the dry ingredients and mixed
for a total of 3.5 min in a 3 speed mixer, (Model A120,Hobart, UK); 450 g of batter was scaled into 1lb tins
and placed in a proofer for 45 min (40 �C, 80% RH).
The batter was baked at 230 �C for 25 min in a reel oven
(Henry Simon, UK). The loaves were cooled to roomtemperature and placed in polyethylene bags until
tested.
2.2. Tests on the loaves
All loaves were measured 24 h after baking. For each
analysis, three loaves from each batch were used. Spe-
cific volume was measured using rapeseed displacement.
Crust and crumb colour was measured using a MinoltaChromameter (Minolta CR-100, Osaka, Japan). L�, a�,b� and L�=b�, were recorded, each value being the av-erage of six measurements. Crust (penetration, cylin-
drical probe; 6 mm diameter) and crumb (texture profile
analysis (TPA), cylindrical probe; 20 mm diameter)
characteristics were assessed using a texture analyser
(TAXT2i, Stable Micro Systems, Surrey, UK). Protein
content of the breads supplemented at the 6% level wasmeasured by the Leco method (AOAC 968.06) and di-
etary fibre content by the AOAC procedure (Fibertec
System E).
2.3. Image acquisition and analysis
Images of the sliced breads (at the 6% level of sup-
plementation) were captured using a flatbed scanner
(Sharp, JX-330, Japan). Images were scanned full scale
at 300 dots per inch and analysed in grey scale (0–255).Image analysis was performed using the UTHSCSA
ImageTool program (Version 2.0, University of Texas
Health Science Centre, San Antonio, Texas, available
by anonymous FTP from maxrad6.uthscsa.edu). A
threshold method was used for differentiating gas cells
and non-cells. The threshold was determined by the
method described by Crowley, Grau, and Arendt (2000).
Analysis was carried out on two subimages of 500� 500pixels selected from within the bread slice. Two slices
were analysed per treatment. Gas cell to total area ratio
was recorded.
2.4. Sensory analysis
Sensory analysis was conducted on trial 1 samples
only and the level of powder incorporation was 6%. As
there were eight products for testing, the sensory anal-ysis took place over two sittings. The first (20 tasters)
involved the control gluten free bread and four breads
containing dairy powders (demineralised whey powder
(dwp), skim milk replacer (smr), skim milk powder
(smp), mpi). The second (20 tasters) session embraced
the same control bread and three breads with dairy
powders (mlk, klc, sodium caseinate (nac)). Panellists
were asked to assess the breads for acceptability, and tomark a 5 cm line (0¼ unacceptable, 5¼ very acceptable)in accordance with their opinion. Results for the two
sessions were analysed separately.
Table 1
Name, type and protein content of the dairy powders
Name Type Protein content (%)
Molkin (mlk)a Sweet whey 6.5
Demineralised whey
powder (dwp)aDemineralised
whey
11.0
Kerrylac (klc)a Fresh milk solids 18.0
Skim milk replacer
(smr)aSpray dried milk
solids
26.0
Skim milk powder
(smp)aSpray dried skim
milk
35.0
Sodium caseinate (nac)a Casein 89.0
Milk protein isolate
(mpi)aProtein isolate 90.0
aAbbreviated names used in the text.
154 E. Gallagher et al. / Journal of Food Engineering 56 (2003) 153–161
2.5. Statistical analysis
Results were analysed using one way analysis of
variance (ANOVA) using SAS (Version 6.12, SAS In-
stitute Inc., Cary, NC, USA) as 7 powders� 4 inclusionlevels (0%, 3%, 6%, 9% powder addition)� 3 replicates(trial 1) and as 3 powders� 3 water levels� 3 replicates.The taste panel tests were analysed (ANOVA) as two
separate sets, i.e. 5 samples� 20 tasters, and 4 samples�20 tasters.
3. Results and discussion
Data for the effects of dairy powders and levels of
inclusion on gluten free bread quality are presented in
Figs. 1–11 together with probability (F-test) and stan-
dard error of the difference (s.e.d.) values. Many of the
effects were statistically significant as were interactionsbetween powder type and inclusion levels. The powders
are in the order lowest to highest protein content (and
vice versa for lactose) reading from left to right in each
figure.
3.1. Loaf volume
Inclusion of dairy powders had a variable effect on
loaf volume (Fig. 1) and there were differences (P <0:001) both between the powders and between the in-clusion levels. Overall, inclusions of dairy powders re-
duced loaf volume by about 6%. This is similar to thefindings of Erdogdu-Arnoczky, Czuchzjowska, and
Pomeranz (1996), Gelinas, Audet, Lachance, and Va-
chon (1995) and Kadharmestan, Baik, and Czucha-
jowska (1998). However, increasing inclusions gave a
recovery in loaf volume in the case of mlk, nac and mpi,
whereas the opposite was the case for dwp, klc and to a
lesser extent smp (Fig. 1). Sodium caseinate and mpi
have a high water holding capacity. With increasinglevels of addition of these powders, the resulting batters
became visibly more viscous, i.e. less like a batter and
more like a dough. These breads had an appealing
shape and were more similar in appearance to wheaten
breads.
3.2. Crust and crumb colour
The lightness of the gluten free bread crust varied
widely with L� values ranging from 62 (3% smp inclu-
sion) to 36 (9% nac inclusion) (P < 0:001). Breads con-taining the dairy powders were generally darker when
compared to their gluten free controls (Fig. 2). The
lower L� values were expected were due to Maillardbrowning and carmelisation which are influenced by the
distribution of water and the reaction of reducing sugars
and amino acids (Kent & Evers, 1994). L� values con-
tinued to decrease with increasing levels of powder in-
corporation but the effect was generally small except for
the high protein-containing powders smr, nac and mpi
where incorporation beyond 6% may be impractical.
Guy (1984) encountered similar darkening effects inwheaten breads. The darkening of the crust colour due
to the inclusion of dairy powders is desirable as gluten
free breads tend to have a lighter crust colour than white
wheaten breads (L� ¼ 38) (Gallagher & Gormley, 2002).Crumb colour ðL�=b�Þ (white/yellow ratio) was influ-
enced both by powder type (P < 0:001) and by level ofaddition (P < 0:001) (Fig. 3). Molkin, klc, smr (with theexception of the lowest inclusion level) and smp resultedin crumb darkening compared with the control gluten
free bread, while nac resulted in a whiter crumb; mpi
inclusion had no effect. These results are a reflection
of the L�=b� ratios for the control gluten free flourðL�=b� ¼ 13:3Þ and of the ‘neat’ dairy powders i.e. mlk(5.3), dwp (6.1), klc (4.9), smr (6.9), smp (7.6), nac (9.3)
and mpi (13.9).
Fig. 1. Influence of dairy powders and their level of inclusion, on the loaf volume of gluten free breads. F-test: powders (P) (P < 0:001; s.e.d. 9.8);
inclusion level (L) (P < 0:001; s.e.d. 7.4); interaction P � L (P < 0:001; s.e.d. 19.5).
E. Gallagher et al. / Journal of Food Engineering 56 (2003) 153–161 155
3.3. Crust and crumb softness
The inclusion of mlk, dwp, klc and smr (i.e. the lower
protein-content powders) in gluten free breads resulted
in a much softer (P < 0:001) crust than the control
gluten free loaves (Fig. 4). This is due to moisture mi-
gration from the crumb. The moisture contents of the
gluten free breads with the dairy powders were fairly
similar and were in the range 39–42%. The inclusion of
smp increased crust hardness but the control gluten free
Fig. 2. Influence of dairy powders and their level of inclusion, on the crust colour of gluten free breads (low values indicate darker crust). F-test:
powders (P) (P < 0:001; s.e.d. 1.2); inclusion level (L) (P < 0:001; s.e.d. 0.9); interaction P � L (P < 0:001; s.e.d. 2.4).
Fig. 3. Influence of dairy powders and their level of inclusion, on the crumb colour of gluten free breads (higher values indicate the whiter crumb).
F-test: powders (P) (P < 0:001; s.e.d. 0.05); inclusion level (L) (P < 0:001; s.e.d. 0.04); interaction P � L (P < 0:001; s.e.d. 0.09).
Fig. 4. Influence of dairy powders and their level of inclusion, on the crust hardness (penetration value) of gluten free breads. F-test: powders (P)
(P < 0:001; s.e.d. 46.8); inclusion level (L) (P < 0:005; s.e.d. 35.4); interaction P � L (P < 0:001; s.e.d. 93.7).
156 E. Gallagher et al. / Journal of Food Engineering 56 (2003) 153–161
bread from this set had a much softer crust than the
controls for the other sets (Fig. 4) and so this result may
be atypical. Both nac and mpi had a minimal effect on
crust hardness, due, presumably to their high protein
content which is strongly water-binding, and thus
minimised moisture migration to the crust.
Fig. 5. Influence of dairy powders and their level of inclusion, on the crumb TPA of gluten free breads. F-test: powders (P) (P < 0:001; s.e.d. 31.0);
inclusion level (L) (P < 0:001; s.e.d. 23.5); interaction P � L (P < 0:001; s.e.d. 62.1).
Fig. 6. Influence of dairy powders (6% inclusion level) on taste panel acceptability score (0 ¼ unacceptable; 5¼ very acceptable) of gluten free breads.F-test: Session 1; (P < 0:05, s.e.d. 0.33). Session 2; (P¼NS, s.e.d. 0.32).
Fig. 7. Influence of dairy powders plus additional water (10% or 20%) on the loaf moisture content of gluten free breads. F-test: powders (P)
(P < 0:05; s.e.d. 1.69); inclusion level (L) (P < 0:005; s.e.d. 0.68); interaction P � L (P < 0:001; s.e.d. 2.32).
E. Gallagher et al. / Journal of Food Engineering 56 (2003) 153–161 157
Fig. 8. Influence of dairy powders plus additional water (10% or 20%) on the loaf volume of gluten free breads. F-test: powders (P) (P < 0:005; s.e.d.
6.5); inclusion level (L) (P < 0:005; s.e.d. 4.2); interaction P � L (P < 0:005; s.e.d. 16.5).
Fig. 9. Influence of dairy powders plus additional water (10% or 20%) on the crust hardness (penetration value) of gluten free breads. F-test: powders
(P) (P < 0:001; s.e.d. 48.4); inclusion level (L) (P < 0:001; s.e.d. 36.8); interaction P � L (P < 0:001; s.e.d. 96.8).
Fig. 10. Influence of dairy powders plus additional water (10% or 20%) on the crumb TPA (firmness) of gluten free breads. F-test: powders (P)
(P < 0:005; s.e.d. 34.1); inclusion level (L) (P < 0:001; s.e.d. 26.8); interaction P � L (P < 0:001; s.e.d. 70.4).
158 E. Gallagher et al. / Journal of Food Engineering 56 (2003) 153–161
In contrast, all the powders reduced crumb softness
(P < 0:001) of the gluten free breads as indicated byhigher crumb hardness values (Fig. 5). The extent of theeffect varied with the level of inclusions, and from
powder to powder. However, breads with the higher
protein-content powder tended to have the firmest (least
soft) crumb compared to the control (0% inclusion).
Molkin was an exception in that it is a low protein-high
lactose powder but still gave a firm crumb (Fig. 5).
Dairy proteins contain strong water absorptive
properties, which may, in turn, lead to finer, densercrumb structures in the baked product Stahel (1983).
This was particularly evident for the breads containing
smp and mpi (P < 0:001). A strong positive correlationwas obtained in the current study between crumb
hardness and loaf volume (r ¼ 0:86, P < 0:001). Kadh-armestan et al. (1998) found similar increased crumb
hardness properties in studies involving whey protein
concentrate in wheat bread. Such firming may be at-tributed to the retrogradation of the wheat starch frac-
tion as described by Schoch and French (1947). Also, it
must be noted that gluten present in wheat-containing
bread slows the movement of water (Roach & Hoseney,
1995) by forming an extensible protein network, thus
keeping the crumb structure softer. Therefore, the ab-
sence of gluten will increase the movement of the water
from bread crumb to crust, thereby resulting in a firmercrumb and a softer crust. However, although the crumb
was firmer for those breads containing the dairy pow-
ders in the current study, it was more similar both
physically and texture-wise to that of ordinary wheat-
containing bread than to the cake-like appearance of
gluten some free breads.
3.4. Image analysis
There was considerable variation in the gas cell to
total area ratio depending on the additive (P < 0:001).The overall mean (38%) was comparable to previouslyreported values (33%, Crowley et al., 2000; 46%, Sa-
pirstein, Roller, & Bushuk, 1994). There was a pro-
gression in the data with the low protein-containing
powders giving the largest gas cells (Table 2). The dwp
was the exception to this trend as it has a low protein
content but gave a smaller number of gas cells. The
addition of mlk was the only treatment that resulted in a
larger gas cell to total area ratio compared to the control
(P < 0:001). There was an inverse rank correlation co-efficient of �0.56 between gas cell size and loaf volume;ie greater numbers of small gas cells gave a higher loaf
volume.
3.5. Sensory analysis
In the first session, three out of the four gluten freebreads were given a higher acceptability score than the
gluten free control (Fig. 6). Bread containing smp was
judged to be significantly more acceptable than the other
samples (P < 0:05). In the second session, a similartrend was observed, i.e. all breads containing the dairy
received higher acceptability scores than the control but
the effect was not statistically significant (Fig. 6).
3.6. Effect of additional water
The moisture content of the breads in trial 2 proved
to be a major factor regulating the loaf volume and
crumb and crust texture (Fig. 7). Increasing water ad-
dition in the batter by 10% and 20% resulted in loaf
volumes being increased in the breads containing allthree powder types with volumes peaking at the 10%
extra level of inclusion (Fig. 8). Both crust (Fig. 9) and
crumb (Fig. 10) hardness were reduced (P < 0:001) withincreasing water addition. However, the level of water
Table 2
Gas cell to total area ratio (%) for the gluten-free breads
Control mlk dwp klc smr smp nac mpi
43 64 31 53 33 20 28 33
Fig. 11. Protein content of gluten free breads supplemented (6% inclusion) with dairy powders.
E. Gallagher et al. / Journal of Food Engineering 56 (2003) 153–161 159
reduction was excessive and resulted in loaves thatwere too soft for ‘easy’ slicing. Starch retrogradation
is strongly influenced by the moisture content of the
product (Maleki, Hoseney, & Mattern, 1980; Morad &
Wakeil, 1976) and the texture results in trial 2 may be
attributed to a reduction in starch retrogradation due to
the presence of extra water, resulting in a softer crumb
overall. These results agree with previous work by
Rogers, Zeleznak, Lai, and Hoseney (1988).
3.7. Nutritional aspects
Gluten free breads supplemented at the 6% level with
the high protein-content powders had double the pro-tein content of the control, i.e. 4.9% (nac) and 5.0%
(mpi) vs 2.4% (control) (Fig. 11). Inclusion of the dairy
powders had no effect on the dietary fibre content of the
gluten free breads and the mean value of 1.4% was much
lower than that (�3.7%) found in white wheat breads(Ranhorta & Gelroth, 1988).
Supplementation of the gluten free breads with the
high lactose-content powders is not suitable for coeliacswho have significant damage to their intestinal villi as
they may be intolerant of lactose due to the absence
of the lactase enzyme which is generated by the villi
(Ortolani & Pastorello, 1997).
4. Conclusions
The seven dairy powders tested had variable effects
on the quality parameters of the gluten free breads. Ingeneral, powders with a high protein (smp, nac, mpi)
content gave breads with a lower loaf volume but with
an increased crumb and crust hardness. However, these
breads had an appealing dark crust and white crumb
appearance, and received good acceptability scores in
sensory tests. When additional water was added to the
gluten free formulation supplemented with mlk, klc and
mpi (6% inclusion), the resulting breads exhibited in-creased volume and a much softer crust and crumb
texture than the controls. Supplementing the gluten free
formulation with high protein-content dairy powders
doubled the protein content of the breads. The dietary
fibre content of the loaves was low but this issue will be
addressed in future trials where the gluten free formu-
lation will be supplemented with inulin.
Acknowledgements
We would like to thank Aidan Morrissey and Francis
Butler for their assistance in this study. This study is
funded by the FIRM Programme as part of the Irish
National Development Plan.
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