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Effect of addition of sourdough on physicochemical characteristics of wheat and rice flour bread

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Gluten-free bread has been developed for people suffering from celiac disease. Nonetheless, the lack of gluten can change the quality of the bread. This study investigated the effect of the addition of sourdough on the physicochemical characteristics of wheat bread and gluten-free bread. In wheat bread, the addition of sourdough (0–15 g per 100 g dough) had no significant effect on the moisture content of the bread. However, the moisture content increased when the sourdough content increased to 22.5–30.0 g per 100 g dough. The addition of sourdough (up to 30 g per 100 g dough) decreased the hardness of the gluten-free bread from 28.94 to 14.95 N. The springiness of the gluten-free bread significantly (P ≤ 0.05) increased from 0.54 to 0.81 with the addition of 22.5–30.0 g per 100g dough sourdough. Likewise, the springiness of the wheat bread significantly increased (P ≤ 0.05) from 0.91 to 0.99. However, with the addition of 30 g sourdough per 100g dough, the hardness of the wheat bread increased significantly (P ≤ 0.05). The cohesiveness of both breads significantly (P ≤ 0.05) increased with an increase in the sourdough content. The addition of sourdough had no significant effect (P > 0.05) on the crust color, but affected the crumb color significantly (P ≤ 0.05). Therefore, the addition of sourdough could change the characteristics of both wheat and gluten-free breads. Keywords: sourdough, gluten-free, bread, wheat, Jasmine rice
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Kasetsart J. (Nat. Sci.) 48 : 964 - 969 (2014)
Department of Product Development, Faculty of Agro-Industry, Kasetsart University, Bangkok 10900, Thailand.
* Corresponding author, e-mail: faginwt@ku.ac.th
Received date : 01/04/14 Accepted date : 11/09/14
INTRODUCTION
Bread is a staple food consumed
worldwide and its consumption is continually
increasing (Novotni et al., 2012). It normally
contains gluten from wheat our because gluten is
responsible for the elastic and extensible properties
which are required to produce good quality bread
(Gallagher et al., 2003). However, the gluten can
be harmful to consumers who suffer from celiac
disease and for this reason, gluten-free bread
has been developed for those people (Arendt
et al., 2008). The lack of gluten can deteriorate
bread quality (Sivaramakrishnan et al., 2004)
Effect of Addition of Sourdough on Physicochemical Characteristics
of Wheat and Rice Flour Bread
Suparat Jitrakbumrung and Nantawan Therdthai*
ABSTRACT
Gluten-free bread has been developed for people suffering from celiac disease. Nonetheless, the
lack of gluten can change the quality of the bread. This study investigated the effect of the addition of
sourdough on the physicochemical characteristics of wheat bread and gluten-free bread. In wheat bread,
the addition of sourdough (0–15 g per 100 g dough) had no signicant effect on the moisture content of
the bread. However, the moisture content increased when the sourdough content increased to 22.5–30.0
g per 100 g dough. The addition of sourdough (up to 30 g per 100 g dough) decreased the hardness of
the gluten-free bread from 28.94 to 14.95 N. The springiness of the gluten-free bread signicantly (P
0.05) increased from 0.54 to 0.81 with the addition of 22.5–30.0 g per 100g dough sourdough. Likewise,
the springiness of the wheat bread signicantly increased (P ≤ 0.05) from 0.91 to 0.99. However, with
the addition of 30 g sourdough per 100g dough, the hardness of the wheat bread increased signicantly
(P ≤ 0.05). The cohesiveness of both breads signicantly (P ≤ 0.05) increased with an increase in the
sourdough content. The addition of sourdough had no signicant effect (P > 0.05) on the crust color,
but affected the crumb color signicantly (P ≤ 0.05). Therefore, the addition of sourdough could change
the characteristics of both wheat and gluten-free breads.
Keywords: sourdough, gluten-free, bread, wheat, Jasmine rice
and consequently, it is necessary to add some
ingredients or apply other methods to improve the
quality of gluten bread to be comparable to that of
wheat bread.
Sourdough is a mixture of flour and
water fermented with lactic acid bacteria (LAB)
and can be used for sourdough bread production
(Diowksz and Ambroziak, 2006). Sourdough
contains lactic acid and acetic acid resulting
in a sour taste of the end product. The action
of sourdough could be responsible for the
characteristics of sourdough bread in terms of acid
production, aroma and leavening, resulting in an
improvement in the volume, texture, avor and
Kasetsart J. (Nat. Sci.) 48(6) 965
nutritional value (Espinosa et al., 2011). In wheat
bread, the addition of 20% sourdough increased
CO2 production and thereby decreased the crumb
hardness (Sandra et al., 2012). Higher addition
of sourdough (30 g per 100 g dough) provided
a protective effect with regard to bread staling
and extended the shelf life of the bread (Torrieri
et al., 2014). In gluten-free bread, Novotni et al.,
(2012) reported that the addition of 15.0–22.5 g
sourdough per 100 g batter could improve the
volume and texture signicantly. The glycemic
index of bread was also decreased to a low level.
In the current research, sourdough was
added to both wheat our and rice our dough. Its
effect on the quality of the developed regular and
gluten-free bread was investigated.
MATERIALS AND METHODS
Materials
Wheat our (12–14% protein) (Hong
Kaw, Bangkok, Thailand), jasmine rice our (Kwao
Dawk Mali 105; Pechpanthong; Roi Et, Thailand),
soy protein (Pro 500A; Vicchi Enterprises;
Bangkok, Thailand), dry yeast (Bruggeman;
Ghent, Belgium), sugar (Mitr Phol; Suphanburi,
Thailand), salt (PrungThip; Nakornratchasima,
Thailand), butter (Allowrie; Bangkok, Thailand),
hydroxypropyl methylcellulose (Methocel K4M;
Vicchi Enterprises; Bangkok, Thailand), milk
(Dutch Mill; Nakhon Pathom, Thailand), egg (CP
Ltd; Chonburi, Thailand) and sourdough starter
(King Arthur Flour; Norwich, VT, USA) were used
to make the wheat bread and gluten-free bread.
Sourdough preparation
Wheat our or jasmine rice our (200 g)
and water (100 g) were mixed with the sourdough
starter (28 g) and fermented at 30 °C and 95%
relative humidity (RH) until the pH reached 4.00
± 0.05 (Novotni et al., 2012).
Bread making
 Wheatourbreadmaking
All ingredients (Table 1) and sourdough
were mixed in a blender (Kenwood Electronics,
Havant, England) at speed 2 for 2 min. Then, butter
was added and continuously mixed at speed 2 for
15 min. The dough was kneaded and placed in a
mold and allowed to prove at 35 °C and 95% RH
(modied from Therdthai et al., 2007) using a
prover for 60 min. Finally, the dough was baked
in a conventional oven at 195 °C for 30 min and
cooled at room temperature (25 °C) for 60 min.
 Riceourbreadmaking
A ll dry ing re dients (Ta ble 1) and
Table 1 Ingredients used in bread formulas.
Ingredient (g) Bread type
Wheat our Rice our
Wheat our 100.0 -
Jasmine rice our - 100.0
Soy protein - 4.0
Baker’s yeast 1.8 1.6
Sugar 4.0 18.0
Salt 1.0 1.0
Water - 75.0
Butter
HPMC
5.0
-
20.0
4.0
Milk 65.0 -
Egg 6.5 -
Source: Adapted from Nishita et al. (1976)
Kasetsart J. (Nat. Sci.) 48(6)
966
sourdough were mixed in the blender at speed 2
for 2 min. Then, butter was added and continuously
mixed at speed 2 for 3 min. The batter was kneaded
and placed in a mold and allowed to prove at 35
°C and 95% RH (modied from Therdthai et al.,
2007) using a prover for 120 min. Finally, the
batter was baked in a conventional oven at 195
°C for 30 min and cooled at room temperature (25
°C) for 60 min.
A completely randomized design was
used to determine the effect of the sourdough
content (0, 7.5, 15.0, 22.5 and 30.0 g per 100 g
dough) on the quality of wheat our bread and rice
our bread.
Determination of bread quality
Moisture content
Bread crumbs (20 mm diameter) were
sampled from the center of the loaf to measure
the moisture content using an oven method
(Association of Official Analytical Chemists,
1990).
 Textureproleanalysis
The bread was cut into 15 × 15 × 15 mm
cubes to measure the texture prole (15 cubes per
measurement). The texture prole was analyzed
using a texture analyzer (TA-XT plus; Charpatech
Center; Bangkok, Thailand) and a P50 cylinder
probe. The testing speed was set to 20 mm.s-1 at
60% deformation.
Crust and crumb color
Color was measured for samples of the
bread crust and crumbs based on the CIE L*,
a* and b* system (Furlan et al., 2015) using a
spectrophotometer (Model CM - 3500d; Minolta;
Ramsey, NJ, USA). The values for L*, a* and
b* represent lightness, greenness-redness and
blueness-yellowness, respectively.
Statistical analysis
Analysis of variance was carried out
using the SPSS software package (version 12.0;
SPSS Inc, Chicago, IL, USA) with signicance
tested at the 95% condence level and differences
among means were determined using the least
signicant difference and Duncan’s test.
RESULTS AND DISCUSSION
Effectofourtypeandsourdoughcontenton
moisturecontentofwheatourandriceour
bread
Table 2 shows the moisture content of
the wheat our bread and the rice our bread
with and without the addition of sourdough. The
addition of sourdough (0–15.0 g per 100 g dough)
had no signicant effect on the moisture content
of the wheat our bread. However, increasing
the sourdough content to 22.5–30.0 g per 100g
dough increased the moisture content of the wheat
our bread. The nal moisture content of the rice
our bread signicantly increased from 37.97 to
44.20% (wet basis; wb) with an increase in the
sourdough content from 0 to 30 g per 100 g dough
because the addition of sourdough increased the
amount of water in the wheat dough and rice batter.
(Torrieri et al. (2014) reported that an increase in
the sourdough content from 20 to 30 g per 100
g dough increased the water content by 2–25%,
depending on the type of starter used.
Table 2 Moisture content of wheat flour and rice flour bread.
Bread type
Moisture (%)
Sourdough (g per 100g dough)
0.0 7.5 15.0 22.5 30.0
Wheat our 40.01 ± 0.06c40.40 ± 0.03bc 41.20 ± 0.01abc 41.96 ± 0.16ab 43.60 ± 0.01a
Rice our 37.97 ± 0.01e38.54 ± 0.03d39.81 ± 0.04c43.71 ± 0.01b44.20 ± 0.08a
a-e = Means ± SD within the same row with different lowercase superscript letters are signicantly different (P ≤ 0.05).
Kasetsart J. (Nat. Sci.) 48(6) 967
Effectofourtypeandsourdoughcontenton
thetextureofwheatourandriceourbread
The analysis of the texture prole of
the wheat our bread showed that the hardness
decreased significantly with an increase in
the sourdough content because the sourdough
improved gas retention in the bread dough.
Moreover, acidication caused by the sourdough
impacted on the solubility of the structure-forming
components such as gluten, starch and protein
(Gobbetti et al., 2008). However, the addition of
sourdough at 30 g per 100 g dough increased the
hardness of the wheat our bread signicantly
because the addition of too much sourdough
affected the growth of yeast and thereby the bread
volume expansion and density. In addition, the
springiness and cohesiveness of the wheat our
bread increased signicantly with the increased
sourdough content (Table 3) because sourdough
created a spongy structure in the bread which
was reected in the increased springiness and
cohesiveness.
Similarly, in the rice bread, the addition of
sourdough (up to 30 g per 100 g dough) decreased
hardness signicantly from 28.94 to 14.95 N due to
the increased gas retention in the dough (Gobbetti
et al., 2008). Furthermore, the springiness of the
rice our bread increased signicantly from 0.54 to
0.81 with the addition of 22.5 and 30.0 sourdough
g per 100 g dough. Likewise, the cohesiveness
of the rice flour bread increased significantly
with the increased sourdough content (Table
4). This coincided with the report of Diowksz
and Ambroziak, (2006) that sourdough strongly
inuenced the crumb structure.
Effectofourtypeandsourdoughcontenton
colorofwheatourandriceourbread
The L*, a* and b* values of the wheat
our bread crust were in the ranges 38.95–52.69,
11.48–14.89, and 22.62–29.82, respectively.
There was no signicant difference among the
wheat our bread crusts. However, the L* values
of the wheat our bread crumb decreased with
Table 3 Texture of wheat flour bread.
Bread type
Sourdough
(g per 100 g
dough)
Hardness (N) Springiness Cohesiveness Gumminess Chewiness (N) Resilience
Wheat our
0.0 4.43 ± 0.10a0.91 ± 0.09c0.67 ± 0.02e3.65 ± 0.16a3.45 ± 0.21a0.31 ± 0.01e
7.5 3.77 ± 0.19b0.95 ± 0.07b0.76 ± 0.03d2.94 ± 0.08b2.79 ± 0.26b0.39 ± 0.02d
15.0 1.12 ± 0.05d0.98 ± 0.10a0.83 ± 0.04b1.25 ± 0.42d1.24 ± 0.43d0.46 ± 0.05b
22.5 0.86 ± 0.14e0.99 ± 0.06a0.89 ± 0.18a1.01 ± 0.09e0.94 ± 0.06e0.48 ± 0.04a
30.0 1.80 ± 0.04c0.99 ± 0.07a0.82 ± 0.01c1.35 ± 0.35c1.34 ± 0.36c0.44 ± 0.02c
a-e = Means ± SD within the same column with different lowercase superscript letters are signicantly different (P ≤ 0.05).
Table 4 Texture of rice flour bread.
Bread
type
Sourdough
(g per 100 g
dough)
Hardness (N) Springiness Cohesiveness Gumminess Chewiness (N) Resilience
Rice our
0 28.94 ± 0.92a0.54 ± 0.10c0.31 ± 0.03e 7.23 ± 1.00e3.92 ± 1.19e0.17 ± 0.01d
7.5 26.18 ± 1.35b0.50 ± 0.10d0.38 ± 0.03d 9.98 ± 1.09b5.08 ± 1.42c0.19 ± 0.01c
15 23.92 ± 0.37c0.46 ± 0.07e0.39 ± 0.06c 9.33 ± 1.42c4.38 ± 1.28d0.20 ± 0.04b
22.5 19.35 ± 0.30d0.81 ± 0.01a0.58 ± 0.01a11.52 ± 0.30a9.39 ± 0.28a0.31 ± 0.01a
30 14.95 ± 0.60e0.79 ± 0.04b0.57 ± 0.03b 8.82 ± 0.39d7.01 ± 0.51b0.31 ± 0.02a
a-e = Means ± SD within the same column with different lowercase superscript letters are signicantly different (P ≤ 0.05).
Kasetsart J. (Nat. Sci.) 48(6)
968
the addition of sourdough (Table 5). This was
inuenced by the color of the sourdough starter.
Similar to the wheat our bread, the rice
our bread crust color (L*, a* and b*) was not
signicantly different among the various levels of
sourdough content. However, increased sourdough
content caused a signicant reduction in the L*
values of the rice our bread crumb (Table 6).
Compared to the wheat our bread crumb, the rice
our bread crumb had higher L* values due to the
light color of the rice our.
CONCLUSION
Wheat our and rice our were used to
develop regular and gluten-free bread with various
levels of sourdough content. An increase in the
sourdough content increased the moisture content
of the rice our bread but not of the wheat our
bread. Regardless of the our type, the increased
sourdough content increased the cohesiveness
and decreased the hardness of the bread crumb
signicantly. In addition, the L* values of both the
wheat our and rice our bread crumb decreased
with increased sourdough content. However, the
effect of the addition of the sourdough content on
all types of bread crust was not signicant.
ACKNOWLEDGEMENTS
Financial support from the Thailand
Research Fund (RSA5580017) is gratefully
acknowledged.
Table 6 Crust and crumb color of rice flour bread.
Bread
type
Sourdough
(g per 100 g
dough)
Crust Crumb
L* a* b* L* a* b*
Rice
our
0.0 53.00 ± 23.71a 9.74 ± 5.31a27.48 ± 13.46a71.54 ± 0.05a0.08 ± 0.01e16.38 ± 0.16a
7.5 53.54 ± 21.70a10.94 ± 8.39a26.27 ± 9.09a68.77 ± 0.09c0.76 ± 0.06a18.19 ± 0.43a
15.0 51.07 ± 19.78a11.14 ± 7.75a26.58 ± 10.01a67.60 ± 0.33d0.75 ± 0.11b17.93 ± 0.51b
22.5 51.09 ± 13.70a13.17 ± 5.61a29.80 ± 2.38a67.12 ± 0.16e0.57 ± 0.03d16.72 ± 0.19d
30.0 57.36 ± 14.07a11.64 ±5.83a30.91 ± 2.91a69.11 ± 0.11b0.58 ± 0.05c17.04 ± 0.26c
a-e = Means ± SD within the same column with different lowercase superscript letters are signicantly different (P ≤ 0.05).
Table 5 Crust and crumb color of wheat flour bread.
Bread
type
Sourdough
(g per 100 g
dough)
Crust Crumb
L* a* b* L* a* b*
Wheat
our
0.0 47.90 ± 15.70a13.47 ± 2.35a24.45 ± 9.67a58.12 ± 0.02b0.19 ± 0.05c12.21 ± 0.23b
7.5 45.61 ± 20.13a11.48 ± 3.38a24.66 ± 12.52a57.13 ± 0.01c0.83 ± 0.01a16.54 ± 0.01a
15.0 41.49 ± 12.98a13.39 ± 2.75a22.62 ± 9.41a46.31 ± 1.14e0.20 ± 0.00b11.21 ± 0.77d
22.5 38.95 ± 12.15a14.89 ± 0.66a22.86 ± 9.26a60.84 ± 1.67a0.11 ± 0.06d12.11 ± 0.50c
30.0 52.69 ± 18.13a11.63 ± 2.41a29.82 ± 10.56a50.90 ± 0.07d0.03 ± 0.00e10.66 ± 0.08e
a-e = Means ± SD within the same column with different lowercase superscript letters are signicantly different (P ≤ 0.05).
Kasetsart J. (Nat. Sci.) 48(6) 969
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... The titration acidity of the bread ranged between Table 4). The moisture content of bread produced with flour A was lower and firmness was softer than bread produced with flour B. Therdthai and Jitrakbumrung (2014) reported that the moisture content of sourdough bread was 43.60%. Crowley et al. (2002) determined the moisture content in breads containing different amounts of added sourdough and found it ranged between 44.4-46.3%. ...
... When bread crust colour was evaluated on flour basis, the bread samples prepared with flour A had higher a and b values and lower L value than those made with flour B. In this context, bread made with flour A was found to have a more desirable crust colour. Therdthai and Jitrakbumrung (2014) determined the L, a and b colour values of 30% sour yeast-added breads as 52.00, 11.63 and 29.82, respectively. These differences in crust colour values are thought to vary depending on the formulation, oven temperature and duration. ...
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Gluten-free bread often has low nutritive value, high glycemic index (GI) and short shelf-life. The aim of this research was to investigate the influence of sourdough addition on GI, quality parameters and firming kinetics of gluten-free bread produced by partially baked frozen technology. Sourdough was fermented with a commercial starter of Lactobacillus fermentum and added to bread batter at four levels (7.5; 15; 22.5 or 30%). We determined biochemical characteristics of the sourdough and bread chemical composition, glycemic index in vivo, physical properties and firming kinetics after final rebaking. All breads were enriched with inulin and were high in fiber (>6 g/100 g). Control bread that was prepared without sourdough had medium GI (68). Sourdough addition decreased bread GI. However, only breads with 15 and 22.5% of sourdough had low GI. Moreover, addition of 15 and 22.5% of sourdough had positively affected the quality parameters of partially baked frozen bread: specific volume increased, crumb firmness decreased and firming was delayed. In conclusion, the combined application of sourdough and partially baked frozen technology can decrease glycemic index, improve quality and shelf-life of gluten-free bread. Such breads can be recommended as a part of well balanced gluten-free diet.
Chapter
Gluten is an essential structure-building protein, contributing to the appearance, crumb structure, and consumer acceptability of many baked products. Therefore, the biggest challenge for food scientists and bakers in the area of gluten-free products is probably the production of high-quality gluten-free bread. Market research showed that the majority of breads currently on the market are of very poor quality. In wheat bread, gluten has such a wide range of functions that it is not possible to replace wheat flour with one single ingredient. Good-quality gluten-free bread can only be produced if a range of flours and polymeric substances, which mimic the viscoelastic properties of gluten, are included in the gluten-free formulation. It is recommended to use a range of gluten-free flours rather than just one flour to achieve products with good sensory and textural properties. The addition of a certain percentage of starch to a gluten-free formulation does certainly improve the overall quality of the gluten-free bread. Naturally gluten-free starches such as that from rice, potatoes, or tapioca, rather than wheat starch, should be used for this purpose. Hydrocolloids are an essential ingredient for gluten-free bread production, since they are able to mimic the viscoelastic properties of gluten to a certain extent. Research performed so far suggests that xanthan gum and HPMC are the most suitable hydrocolloids for gluten-free bread formulations. Protein-based ingredients are also essential in the improvement of gluten-free bread, and the most promising are probably the dairy-based ingredients. It is essential that only low lactose dairy ingredients be used. One of the most important ingredients in any gluten-free formulation is water, and therefore it is essential to optimize the water level for every formulation to achieve optimal results.
Chapter
The use of sourdough as the natural starter for leavening is one of the oldest biotechnological processes in food fermentation. Sourdough is a mixture of flour (e.g. wheat, rye), water, and other ingredients that is fermented by naturally occurring lactic acid bacteria and yeasts. Although these microorganisms originate mainly from flours and process equipment, the resulting composition of the sourdough microbiota is determined by endogenous and exogenous factors. In the mature sourdoughs, lactic acid bacteria dominate, occurring in numbers > 108 cfu/g, whereas the number of yeasts is orders of magnitude lower. Three standard protocols are distinguished for sourdough fermentation. Type I sourdough is manufactured with a traditional technique and is characterized by continuous, daily refreshments to maintain the microorganisms in an active state, as indicated by their high metabolic activity. The process is carried out at room temperature (20-30°C) and the final pH of the sourdough is ca. 4.0. Type II sourdough is used as dough acidifier. The fermentation lasts 2-5 days at >30°C to speed up the process and the pH is <3.5 after 24 hours of fermentation. The microorganisms are in the late stationary phase of growth and exhibit restricted metabolic activity. Type III is a dried sourdough in powder form that is fermented by defined starter cultures. It is used as acidifier supplement and aroma carrier during breadmaking.
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The objective of this work was to study the effect of sourdough obtained with selected exopolysaccharide (EPS)-producing lactic acid bacteria (LAB) strains on the quality of bread and its shelf life. Two sourdough concentrations were used in order to ascertain the best bread composition. Fresh bread quality was studied by means of microbiological, physical, chemical and mechanical analysis, whereas physical, thermal and mechanical properties were investigated to study the product shelf life. The results showed that dough prepared with 30 g/100 g of sourdough had a negative impact on bread quality properties in the absence of EPS-producing LAB strains, whereas the opposite was observed in the presence of EPS-producing strains: bread samples at 30 g/100 g of sourdough showed higher volume, higher moisture content and better mechanical properties during storage than samples at 20 g/100 g of sourdough. Moreover, 30 g/100 g of sourdough showed a protective effect on bread staling, thus confirming the effect of sourdough concentration and the positive role of EPS on functional properties.
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The rheological properties of two varieties of rice with Hydroxy propyl methyl cellulose (HPMC) added as gluten substitute were studied using a farinograph and a rheometer and compared with wheat dough to find its suitability for making rice bread. The water absorption and dough development time data were obtained from the farinogram. The tests conducted in the rheometer were oscillation measurements (frequency sweep from 0.1 to 20 Hz at 1% strain), shear measurement (shearing from 0.1 to 5 s−1) and creep tests with an instant loading of 50 Pa for 60 S. Baking tests were conducted with all the dough samples and the loaf volume and moisture loss of bread were measured. The farinogram showed that rice flour supplemented with HPMC reached a consistency of 500 BU at a later time than that of standard wheat dough. The rheological measurements from the oscillation tests and creep tests showed that the rice dough with 1.5% and 3.0% HPMC had similar rheological properties to that of wheat flour dough and was suitable for making rice bread. The long grain rice sample produced a rice bread with better crumb texture.
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Proving is one of the key processes in bread making, where dough normally rests and grows under an environment of constant temperature and humidity. To better understand the effect of relative humidity (RH) and temperature on the kinetics of dough expansion during proving and be able to optimize the growth rate, rice-flour-based dough of same formulation was proved under various process conditions. Both RH and temperature showed significant effect on the dough expansion rate during proving. To describe the dough expansion, a first-order, non-Arrhenius kinetic model was developed. The influence of RH and temperature on the kinetic rate was described by an empirical model. Through verification, the model performance was proved to be reasonably good. The model was subsequently used to optimize the proving condition to maximize the kinetic rate constant therefore minimizing the proving time. The fastest proving condition for the rice-flour-based dough in this research was at 90% RH and 46.3 °C. According to the model, the kinetic rate constant under the optimal condition was estimated to be at 0.217 min−1. From an initial height of 5 mm, the dough height could be increased to 11 mm within 6.4 min.
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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 the inclusion 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 to the 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.