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Effect of arabinoxylans and laccase on batter rheology and quality of yeast-leavened gluten-free breads
Accepted Manuscript Effect of arabinoxylans and laccase on batter rheology and quality of yeastleavened gluten-free breads
Fabiola E. Ayala-Soto, Sergio O. Serna-Saldívar, Jorge Welti-Chanes PII:
S0733-5210(16)30414-3
DOI:
10.1016/j.jcs.2016.11.003
Reference:
YJCRS 2240
To appear in:
Journal of Cereal Science
Received Date:
02 June 2016
Revised Date:
13 October 2016
Accepted Date:
07 November 2016
Please cite this article as: Fabiola E. Ayala-Soto, Sergio O. Serna-Saldívar, Jorge Welti-Chanes, Effect of arabinoxylans and laccase on batter rheology and quality of yeast-leavened gluten-free breads, Journal of Cereal Science (2016), doi: 10.1016/j.jcs.2016.11.003
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ACCEPTED MANUSCRIPT Highlights
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Maize fiber arabinoxylans (MFAX) decreased RVA peak viscosity in gluten free (GF) flour. MFAX addition decreased final RVA viscosity or retrogradation in GF flour. MFAX increased water absorption and benefited bread texture and volume. Laccase did not affect batter rheology nor GF bread quality.
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Effect of arabinoxylans and laccase on batter rheology and quality of yeast-leavened
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gluten-free breads
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Fabiola E. Ayala-Sotoa, Sergio O. Serna-Saldívara*, Jorge Welti-Chanesa
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Tecnológico de Monterrey. Escuela de Ingeniería y Ciencias. Centro de Biotecnología-
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FEMSA. Av. Eugenio Garza Sada 2501 Sur, C.P. 64849 Monterrey, N. L. Méxicoa.
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*Corresponding
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Sergio O. Serna-Saldívar
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Tecnológico de Monterrey. Escuela de Ingeniería y Ciencias. Centro de Biotecnología-
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FEMSA.
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Av. Eugenio Garza Sada 2501 Sur, C.P. 64849 Monterrey, N. L. México.
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Tel. +52 (81) 83284322;
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Fax. +52 (81) 83284262;
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e-mail:[email protected]
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author:
ACCEPTED MANUSCRIPT The supplementation effects of maize fiber arabinoxylans (MFAX, 0%-6%), laccase (0-2 U/g
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flour) and water absorption level (90%-100%) on gluten-free (GF) batter rheology and bread
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quality were analyzed. From viscoamylograph analysis, lower starch amount in GF flour due
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to MFAX addition decreased peak viscosity and retrogradation. Surface response plots
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showed that laccase did not have significant effect on GF batter rheology and bread quality,
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whilst water was the most important variable. Higher levels of water absorption benefited
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bread texture. Higher water level (>100 mL/100 g flour) was needed in the experimental
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design to evaluate correctly the effect of 6% MFAX replacement on GF bread quality. Further
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analyses were carried in order to adjust water absorption of batters according to their
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consistency index (K≈100 Pa sn), resulting an optimal water absorptions of 95%, 100% and
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105% for control flour and flours supplemented with 3% or 6% MFAX, respectively. Thus,
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MFAX addition enhanced water-binding capacity of flour and yielded GF breads with higher
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specific volume and softer crumb texture. These quality parameters were best rated with 6%
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MFAX addition to flours. This research demonstrated the potential of MFAX to develop GF
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breads with improved quality, when optimal water level is used.
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Keywords: maize fiber arabinoxylans (MFAX), batter rheology, gluten-free (GF) bread,
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response surface methodology (RSM). Introduction
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4.1.
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Bakery products are important staples for practically all consumers around the world. Wheat
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is unique as a raw material for the production of yeast-leavened products such as breads and
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pastries. However, there is a group of individuals that suffer conditions such as coeliac
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disease, allergy, gluten ataxia and non-celiac gluten sensitivity. These disorders are triggered
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by the consumption of prolamin fractions derived from wheat (gliadin), rye (secalin) or barley
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(hordein) (Rosell et al., 2015). The only treatment to gluten related disorder consists on
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gluten-free (GF) diet, in which food products must contain lower than 20 ppm of total gluten.
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The absence of gluten produces technological problems in the production of baked goods. GF
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doughs are more fluid than wheat doughs and closer in viscosity to cake batters due the lack
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of a gluten network (Schoeber et al., 2005). Different gums or hydrocolloids are often
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incorporated in different GF bread formulations to improve dough development and gas
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retention through the increase in system viscosity, producing loaves with higher specific
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volume, better crumb structure, overall acceptability and shelf life (Marco and Rosell, 2008,
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McCarthy et al., 2005).
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ACCEPTED MANUSCRIPT It is known that minor constituents such as non-starch polysaccharides in wheat flour play a
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relevant role in the bread making process (Biliaderis et al., 1995). AX are non-starch
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polysaccharides from the endosperm cell walls, aleurone layer and the pericarp of cereal
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grains. The structure is mainly constituted of a linear β-(1,4)-D-xylopyranose backbone and
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L-arabinofuranose residues as side chains on O-2 and/or O-3. Some of the arabinose moieties
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are ester-linked on O-5 positions to hydroxycinnamic acids (HCA) such as ferulic acid (FA)
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and p-coumaric acid (p-CA) (Saulnier et al., 2007). AX are subdivided into water-extractable
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(WEAX) and unextractable (WUAX) fractions. Previous studies have reported that WEAX
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have significant effects on dough properties and quality bread parameters such as loaf volume,
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crumb texture and staling characteristics; which may impact positively or negatively
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depending on flour quality, water absorption level and experimental design (Biliaderis et al.,
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1995; Courtin and Delcour, 2002; Hemalatha et al., 2013). The influence of this polymer has
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been related to the enhancement of viscosity, water holding capacity and gelation especially
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when oxidants such as laccase enzyme are employed (Courtin and Delcour, 1998). Moreover,
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due to their nature as soluble fiber and the presence of ferulic acid in their structure, AX also
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exert health benefits in controlling diabetes mellitus, cardiovascular disorders, improving
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colon function, activity against some types of cancer and immunological disorders (Zhou et
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al., 2010; Ogawa et al., 2011; Rose et al., 2010; Saeed et al., 2011).
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Few previous studies have shown an insight of the potential application of AX from in GF
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products (Mansberger et al., 2014). However, no evidence exists about the behavior of the
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polymer extracts in the development and features of GF breads. Due to their interesting
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functionalities in wheat or rye breads, AX may physically and nutritionally improve the
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quality of GF batter and bread. The present study is the first showing the potential application
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of MFAX for the improvement of the properties of GF breads. In order to evaluate the
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technological application of AX on GF bread formulations, the present study was undertaken
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to determine the viscoamylograph changes (related to starch retrogradation) of composite GF
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flour supplemented with MFAX. Likewise, by response surface methodology it was assessed
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the effects of MFAX, dough water absorption level and laccase activity on the rheology of GF
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batters and quality of corresponding GF breads especially in terms of specific volume and
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crumb hardness.
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4.2.
Materials and methods
4.2.1. Materials
ACCEPTED MANUSCRIPT Composite GF flours, chosen by preliminary studies, had the following formulation: 33% rice
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flour, 32% corn starch, 22% brown rice flour, 5% pregelatinized corn starch, 4% egg albumin
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and 4% soy protein isolate, determined from technical information of ingredients. The
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composite formulation contained 13.1% moisture, 12.06% protein, 0.98% lipids, 79.22% non-
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fibrous carbohydrates and 1.10% crude fiber. Salt, sugar, dry yeast and corn oil were
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purchased from the local market.
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Spray-dried MFAX were extracted under alkaline conditions and characterized as reported by
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Ayala-Soto et al., (2016). Triplicates of 100 g of maize fiber were suspended in 0.3 M sodium
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hydroxide (1:15 w/v agitated at 150 rpm) during 6 h at 60°C by using a glass beaker (capacity
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3 L) covered with aluminum foil. The temperature was controlled through a magnetic stirring
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hot plate (Thermo Scientific, USA). Following, the suspension was centrifuged at 4500 g for
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15 min at 20°C (IEC CL40R, Thermo Scientific, France) and the resulting supernatant
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acidified to pH 4 with 3 N hydrochloric acid. The precipitated hemicellulose A was separated
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through centrifugation (4500 g for 15 min at 20°C) and the acidified supernatant was mixed
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with 96% ethanol (55% v/v) in order to enhance the precipitation of hemicellulose B. The
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solution was allowed to precipitate at 4°C overnight. The ethanol supernatant was separated
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using a peristaltic pump (mini-pump variable flow, Fisher Scientific, USA). A second
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precipitation of the AX extract was performed with 55% ethanol to decrease the content of
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ethanol soluble compounds in the extract. The content of ethanol in the precipitate was
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evaporated using rotary evaporation under vacuum at 80 mbar at 55°C and 100 rpm
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(Rotavapor R-220 Büchi, Switzerland). During this process water was added to decrease the
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high viscosity of the extract. In preparation for spray, the solids of the AX solution was
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adjusted to 2.9% ± 0.3% and were set with inlet and outlet temperatures of 190°C and 90°C,
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respectively and a flow rate of 570 mL/h (Spray drier 311S YAMATO Scientific Co, Japan).
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The MFAX polymer had a composition of 97.34% carbohydrates, 1.79% protein, 0.21%
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lipids (expressed on dry weight basis); A/X 0.69; molecular weights of 811 kDa and 756 kDa,
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with distributions of 12.18% and 87.89%; average hydrodynamic radius of 380.2 nm; and
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1.5% of terminal xylose linked directly to the backbone. This value is related to the branching
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degree of the structure and represents an extract with lower branching structure compared to
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16% of terminal xylose previously reported by Rumpagaporn et al., (2015) in maize AX. The
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thermostable laccase extracted from Pycnoorus sanguineus was provided by the Emerging
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and Molecular Nutrition research chair of Tecnológico de Monterrey, México (Ramírez-
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Cavazos et al., 2014).
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4.2.2. Viscoamylograph properties Two levels of MFAX were substituted at the rate of 3% or 6% to the composite GF flour. The
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pasting properties of a control sample and experimental GF flours were determined with the
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Rapid-Visco Analyser (RVA) (RVA 4500, Perten Instruments, USA). Concerning to sample
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preparation, 2.64 g (dry weight basis) of flour samples were weighed directly into the
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aluminum RVA canister, distilled water was added to a total weight of 28 g, and then contents
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mixed. The RVA test profile used was the reported by Storck et al., (2013). The sample was
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held at 50C for 1 min, heated to 95C at a rate of 12C/minute, held at 95C for 2.5 min,
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cooled to 50C at a rate of -12C/minute, and held at 50C for 2.5 min. The rotational speed
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of the paddle was maintained at 160 rpm throughout the assay, except during the first 10 s
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when 960 rpm were applied in order to facilitate the blending of the solids with the water.
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Peak viscosity, breakdown, final viscosity and setback (difference between final viscosity and
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peak viscosity) were evaluated.
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4.2.3. Experimental design
Response surface methodology (RSM) was used to study the effects of MFAX, laccase
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enzyme and water addition on parameters related to bread quality such as specific volume and
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hardness throughout 3 days of storage at room temperature. After preliminary baking tests,
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the upper and lower limits for these variables were established. A completely random Box-
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Behnken design was used and the MFAX levels were 0%–6% of flour replacement, laccase 1-
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2 U/g flour and water absorption level 90%–100% (mL water/100 g flour). Three central
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points and 3 levels of each parameter were selected to perform 15 baking trials (Table 1) in
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duplicates. The analyses of variance (ANOVA) were used to determine the lack of fit and the
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significance of the linear, quadratic and interaction effects of the independent variables on the
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dependent variables.
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4.2.4. Rheology measurements
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GF batters of the experimental formulations were prepared adding the following ingredients
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(percentages calculated on wet flour basis): sugar (6%), salt (1.5%), corn oil (5%), diacetyl-
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tartaric acid ester of monoglycerides (DATEM) (0.3%), and calcium propionate (0.3%). The
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batters were covered with a plastic film in order to avoid loss of moisture and allowed to rest
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for 20 min. Shear viscosities were measured immediately afterwards at 25°C using a
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rotational rheometer (Anton Paar, Austria) equipped with the parallel plates geometry (25 mm,
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gap 1mm). The steady shear viscosity was determined (Kate et al., 2010) from 1 to 100 s-1 and
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the power law model (τ= Kγn) was used to describe the effect of shear rate on the viscosity of
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the samples by determining the consistency index (K) as follow:
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Log τ= n log γ + log K
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Where: τ, shear stress; n, flow behavior index (dimensionless) that reflects the closeness to
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Newtonian flow (n=1); γ, shear rate (s-1); and K, flow consistency index (Pa sn).
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(Eq. 1)
4.2.5. Breadmaking
A straight dough process was performed using a Kitchen-Aid professional mixer
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(KSM150PSER, KitchenAid, St. Joseph, MI, USA) with a wire wipe (K45WW). The
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following ingredients (percentages calculated on wet flour basis or bakers formulation) were
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used: sunflower oil (5%), sucrose (6%), salt (1.5%), dry yeast (2%), yeast food (0.5%),
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sodium propionate (0.3%) and DATEM (0.3%). The variables MFAX, laccase and water were
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added according to the experimental design shown in Table 1. All ingredients were mixed for
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5 min at speed 6 (in a scale 1–10 of the mixer). The batters were fermented for 30 min at
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30°C and 90% relative humidity; then were weighted (24.39 g ± 0.04 g of solid content)
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directly into non-stick mini loaf pan (25 x 55 x 100 mm) and fermented in a proofing chamber
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at 30°C and 90% relative humidity for 30 additional min. After proofing, the batters were
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baked (convection oven, Electrolux, USA) for 8 min at 195°C. Then the bread loaves were
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removed from the pans, cooled for 60 min at room temperature, and packed in sealed
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polyethylene bags to prevent dehydration.
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The loaf weight, bread height and volume were determined after 60 min of bread cooling. The
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volume of each bread loaf was determined by rapeseed displacement. Specific volume (mL/g)
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was obtained by dividing bread volume/bread weight. The moisture content of bread crumb
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was determined by drying 3 g of sample in a forced convection oven at 105°C for 24 h. The
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samples were cooled in desiccators and weighted. Three measurements of each sample were
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performed.
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4.2.7. Texture analysis
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Evaluation of crumb hardness of GF bread was performed the day 0 (3 hours after bread
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making), and day 3. The loaves were stored in polyethylene bags at ambient temperature. The
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crumb texture was determined using a TA-XT2 texture analyzer (Stable Microsystems, Surrey,
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UK) with the ‘‘Texture Exponent’ software (Stable Micro Systems, England). A 60 mm
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diameter perspex compression probe was used in a ‘Texture Profile Analysis’ (TPA) double
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compression test with 25% of strain, with a test speed of 5 mm/s, and a 5 s delay between the
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first and second compressions. Hardness was calculated from the TPA plot. Measurements
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were made on the central part of three slices (15 mm thickness) from breads of each batch. 4.2.8. Statistical analysis
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All analyses were done in triplicate and results expressed as mean ± standard deviations.
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Statistical analyses were conducted by one-way ANOVA, and differences among means were
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compared with Tukey’s tests with a level of significance of P<0.05. Regression analyses,
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Pearson’s correlations and main effect plots were performed to evaluate the relationship
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between variables. Response surface plots were generated from the regression equations only
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for significant interactions obtained by analysis of variance. All statistical analyses were
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performed by using the JMP® Version 11 software (SAS Institute Inc., Cary, NC, USA).
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4.3.
Results and discussion
4.3.1. Effect of MFAX substitution on pasting properties of gluten-free flour
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It is known, that baking properties of starch depend mostly on its swelling and gelatinization
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properties. The composite GF flour pasting properties would be useful to predict its
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performance during processing and phenomenon of bread staling (Arif et al., 2012).
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As shown in Figure 1, the supplementation of the two different levels of MFAX to the GF
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flour significantly affected pasting properties. The substitution of 3% or 6% of MFAX (x)
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correlated negatively (y= -0.105x + 2.07, R2= 0.96) with the average peak viscosity (y).
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Values of control GF flour decreased from 2.1 Pa s to 1.68 Pa s (20.4% lower) and to 1.47 Pa
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s (30% lower) with 3% and 6% of MFAX in flour, respectively. On the other hand, a positive
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correlation existed between MFAX content (x) and the time (y) to achieve peak viscosity (y=
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0.0889x + 5, R2=1). Compared to control GF flour, the replacement of 3% and 6% MFAX
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increased the time to peak viscosity from 5 min to 5.27 min and 5.54 min, respectively. In fact,
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the time increased 0.27 min with each 3% of MFAX substitution in the GF flour.
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From regression analyses, negative correlations existed between the substitution level of
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MFAX in GF flour (x) and the values of breakdown (y=- 0.06 x + 0.451, R2= 0.95) and final
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viscosities (y) (y=-0.18 x + 3.28, R2=0.99). Breakdown viscosities in control GF flour exerted
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the highest average value with 0.48 Pa s, followed by flours supplemented with 3% (0.23 Pa
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s) or 6% MFAX (0.13 Pa s). High values of breakdown are associated with high peak
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viscosities, which in turn, are related to the degree of swelling of the starch granules during
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ACCEPTED MANUSCRIPT heating (Arif et al., 2012). Final viscosity values of the control GF flour (3.29 Pa s) decreased
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17.5% and 32.3% when 3 or 6% MFAX were added to the flour. Concerning to setback
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viscosities (y), regression analysis showed quadratic correlations with the MFAX substitution
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(x) level (y = 0.05 x2 – 0.39 x + 1.66, R² =1). The highest setback viscosity was observed in
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the control GF flour (1.66 Pa s) whereas the lowest value was observed in the flour
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supplemented with 3% MFAX (0.98 Pa s). The addition of 6% MFAX produced an
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intermediate setback viscosity value of 1.27 Pa s.
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The negative correlations of MFAX supplemented flours with peak, breakdown and final
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viscosities, as well as the lower values of setback viscosity are attributed to the lower amount
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of starch in flours and to the hydrophilic nature of MFAX that enhanced the binding of free
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water which decreased the starch pasting properties. The time required to reach the peak
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viscosity is an indirect measurement of the time required for cooking, and higher values are
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related to the utilization of more energy to gelatinize the starch (Arif et al., 2012). The setback
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is usually related to recrystallization of the amylose chains. Therefore, the addition of MFAX
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and the lower starch amount weakened gelling of the GF flour likely decreasing granule
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swelling and starch leaching, and thus decreased GF flour retrogradation, compared to control
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sample.
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Contradictory results related to the effects of AX on pasting properties of flours have been
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previously published. Arif et al., (2012) reported a significantly reduced starch retrogradation
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in white spring wheat flour due to the lower peak and setback viscosities as affected by the
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addition of water-soluble pentosans. However, Sasaki et al., (2000) documented that the
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addition of non-starch polysaccharides increased the peak and breakdown viscosities of wheat
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flour. The discrepancies in results could be due to the different sources from which pentosans
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were isolated and the quality of flour samples analyzed (Arif et al., 2012). In the present study,
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it was utilized water soluble MFAX with high molecular weight (756 kDa-811 kDa) and low
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degree of branching, compared with previous studies conducted by Rumpagaporn et al.,
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(2015). It is known that high molecular AX with low branching structures exhibit higher
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water solubility compared to counterparts with lower molecular weight and higher structure
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complexity (Saulnier et al., 2007).
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4.3.2. Effect of MFAX, laccase and water absorption levels on gluten-free batter rheology
ACCEPTED MANUSCRIPT According to rheograms obtained (not shown here), which related shear stresses vs shear rates,
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all the experimental GF batters showed shear thinning behavior with n values lower than 1
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(n= 0.37 to 0.56), and coefficient of determination R2 close to 0.99 (Eq. 1). The consistency
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index (k), which gives an indication of the viscosity of the fluid, varied from 77 Pa sn to 276
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Pa sn. According to statistical analyses, both the MFAX addition and water absorption levels
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significantly (P<0.05) affected K values whereas addition of laccase did not significantly
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affect this parameter. The consistency index in GF batters increased at higher concentrations
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of MFAX in flour and decreased at higher water absorption levels. The results agree with
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previous investigations, which have demonstrated that AX increased viscosity and thus
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affected functional properties (Courtin and Delcour, 1998; Saeed et al., 2011; Saulnier et al.,
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2007).
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4.3.3. Effect of MFAX, laccase and water absorption levels on GF bread quality
The widely accepted quality criteria for breads are large volume, soft crumb, and a uniform
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crumb grain. The selected parameters to evaluate the effect of MFAX, laccase and water
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amount on quality of GF bread were specific volume and crumb texture or hardness.
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The variable laccase and the interactions MFAX-laccase and laccase-laccase did not have
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significant effects (P>0.05) on specific bread volumes. As shown in response surface plots of
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Figure 2, higher values of specific volume were obtained when MFAX substitution ranged
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from 1% to 3% in GF flour, and when the water absorption levels varied from 96 to 99%. The
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lowest values were observed in breads supplemented with 6% MFAX produced with a water
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absorption level of 90%. The results agreed with the study of Biliaderis et al., (1995) who
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concluded that the relationship between preparation level and bread volume had a maximum
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at certain amount of AX. Addition of 2% AX did not always yield breads with higher volume
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compared to counterparts which only contained 1% of AX (Biliaderis et al., 1995). Mancebo
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et al., (2015) reported similar results with the addition of HPMC to rice-based GF breads.
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They stated that the effect of hydrocolloids depend of dough hydration, which increased
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proportionally when the amount of hydrocolloid augmented. Probably the consistency of
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batters with high level of MFAX was too thick which reduced the expansion of the carbon
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dioxide produced by the yeast during proofing and baking consequently generating breads
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with lower specific volumes. Renzetti et al., (2010) documented that increased batter
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deformability was related to higher specific volumes of GF breads.
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The bread hardness values after 3 days post baking were used for response surface analysis.
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ACCEPTED MANUSCRIPT The water absorption level and the interaction water absorption-MFAX were the parameters
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that affected the most (P<0.05). From surface response plots, lower crumb hardness values
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were associated to GF bread formulations with higher water absorptions (Figure 2). The
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higher water absorption levels in breads have been previously related to texture improvement
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in gluten-free formulations (de la Hera et al., 2014). Water acts as plasticizer lowering rigidity
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in bakery items (Biliaderis et al., 1995). Unlike to specific volume, the substitution of 6%
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MFAX improved the texture of GF breads when produced with water absorptions higher than
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95%. The positive effects of MFAX on texture of GF breads could be due to their strong
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water binding capacity that decreases starch gelatinization (as shown on viscoamylograph
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analysis), stabilizes water and decreases the rate of moisture loss, which have been related to
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the decrease in crumb firmness or staling rate. Additionally, the capacity of AX to interfere in
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the intermolecular associations of both amylopectin and amylose is other reported mechanism
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that reduces bread staling (Courtin and Delcour, 2002).
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Contradictory reports exist concerning to the impact of AX and laccase on bread quality.
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Some of them stated that water-soluble pentosans improves dough rheology and finally results
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in better crumb structure and larger loaf volume (Courtin and Delcour, 2002, Buksa et al.,
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2013) whereas other (Biliaderis et al., 1995) concluded that the higher moisture content of the
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AX-supplemented crumbs increased starch retrogradation by amylopectin recrystallization
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and therefore bread staling. Biliaderis et al., (1995) also showed contradictory results of bread
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staling by DSC and firmness measurements, and concluded that no single technique can
304
provide a complete view of all events related to these phenomena. Different starting materials
305
and isolation techniques for AX, as well as the polymer structure, different bread-making
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recipes and procedures may be responsible of these differences (Courtin and Delcour, 1998).
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Concerning to laccase, other investigations showed significant positive effects of the enzyme
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on bread quality. In this research the addition of laccase did not influence batter rheology nor
309
improved bread quality. Flander et al., (2008) concluded that laccase had detrimental results
310
on specific volume and texture of oat bread. However, Renzetti et al., (2010) reported positive
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results on oat bread. The microbial origin of laccase, the type of flour, AX supplementation
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and water absorption used to produce breads might explain the contradictory results (Renzetti
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et al., 2010). Likewise, the time of fermentation should be a key factor to control in order to
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allow the laccase to enhance AX crosslinking. In the present research the batters were rested
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only 25 min, and breads were manufactured following the straight dough process with only 1
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hour of fermentation. According to previous studies, the used MFAX sample gelled after two
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hours under the action of this enzyme (Ayala-Soto et al., 2016). Probably, for this reason in
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the present research the enzyme did not have a significant effect in batter rheology and bread
319
quality.
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4.3.4. Optimization of gluten-free bread formulations According to the established levels of each variable, the optimization of GF bread
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formulations was performed to maximize the specific volume and minimize bread hardness
323
values after 3 days storage at room temperature. With a desirability of 0.86, the most
324
outstanding GF breads were produced with 3.6% MFAX, 0 U/g laccase and 100% water
325
absorption. The resulting bread had a specific volume of 2.79 mL/g and 58.74 N of hardness
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after 3 days of storage. However, response surface plots indicated that the selected range of
327
water absorption was not enough to optimize bread specific volume and texture in
328
formulations containing 6% MFAX.
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The correct adjustment of water absorption is very relevant for both batter consistency and
330
bread quality especially when formulations are supplemented with AX. As mentioned above,
331
the high water affinity of AX decreases the free water and increases the batter consistency or
332
viscosity. Haque and Morris (1994) mentioned previously that the central problem to resolve
333
for the development of acceptable GF breads consists in adjusting water content to achieve
334
the right consistency. For this reason, K values were determined in order to establish a
335
relationship between dough rheology and parameters related to bread quality such as specific
336
volume and crumb hardness after 3 days of storage. Low correlations resulted between K
337
values and the studied parameters. However, it was possible to detect that breads with the
338
lowest hardness values for each MFAX level had similar batter consistencies. For the control
339
GF flour, the lowest crumb hardness and relative acceptable specific volume (>2.75 mL/g)
340
were observed in breads produced with a water absorption level of 95% whereas for
341
counterparts supplemented with 3% MFAX were 5 units higher or 100%. Both batters had K
342
values of 98 Pa sn and 101.7 Pa sn, respectively. As expected, batters containing 6% MFAX
343
had higher K values (145-276 Pa sn) and needed more water in order to obtain similar
344
consistency values.
345
Given the findings, the next step consisted on water optimization for GF flour enriched with
346
6% MFAX. It was determined as the water absorption needed to form GF batters with K
347
values quite similar to the other samples. Rheograms indicated that this specific formulation
348
required 105% water absorption and produced batters with K values of 107.5 Pa sn. Marco
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ACCEPTED MANUSCRIPT and Rosell (2008) used higher water level (110%) when producing GF rice flour-based breads.
350
Rheological analyses and breads were baked after determining the optimum water absorption
351
levels for the 3 different samples. Laccase was not considered because previous baking trials
352
clearly indicated that it did not improve batter nor bread properties. Table 2 depicts the
353
adjusted K values and the significant differences found for the n parameter for control and the
354
two experimental MFAX supplemented samples. High correlation existed between the water
355
absorption of the batters and n values (r= 0.98). In other words, the higher water addition
356
formed batters with lower shear thinning values and it was independent of the MFAX
357
concentration in flours. For example, the 6% MFAX flour mixed with the highest water
358
absorption (105%) formed batters with n values closer to 1. On the other hand, batters
359
containing 6% MFAX in flour were more resilient to decrease viscosity through the increase
360
of shear rate regardless of the water amount (Figure 3). The presence of MFAX in flour might
361
increase the entanglement between the polymer and ingredients forming a batter with higher
362
resistance to flow through the increase of shear rate.
363
Concerning to the corresponding GF breads, higher water absorption in batters formed breads
364
with higher moisture content and lower water losses (r=97) (Table 2). It is known that there is
365
an acceleration of the retrogradation rate with increasing moisture, especially in the range of
366
20%-45% water content (Biliaderis et al., 1995). In the present study, the moisture content
367
was higher than the cited range. As expected, the control bread contained the lowest moisture
368
whereas the counterpart containing 6% MFAX contained the highest moisture (Table 2).
369
After 3 days of storage, the control GF bread had the lowest moisture loss (1.67%), followed
370
by GF breads produced from formulations containing 6% MFAX (2.72%) and 3% MFAX
371
(3.50%). Despite the water losses, the GF breads with the highest level of MFAX had the
372
softest crumb being 1.7 and 1.5 times lower than control bread at days 0 and 3, whereas the
373
bread containing the lowest level of MFAX did not differ compared to the control bread
374
(Table 2). After 3 days, the control bread had the highest hardness (28.73 N), followed by
375
counterparts with the highest (23.05 N) and lowest MFAX levels (21.38 N).
376
Unlike the predicted results from the Box-Behnken design, the adjustment of water
377
absorption with respect to K values in flour supplemented with 6% MFAX not only formed
378
breads with the softest texture but also with the highest specific volume (Table 2, Figure 4).
379
The selected consistency index value was enough to allow gas bubble to expand during
380
proofing and baking. Furthermore, the addition of water according to the K parameter allowed
381
the formation of breads with uniform crumb loci, especially in breads produced with the
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ACCEPTED MANUSCRIPT highest MFAX concentration. Among breads, the 3% MFAX breads comparatively contained
383
larger loci (Figure 4).
384
In addition to the known plasticizing effect of water, previous studies have reported that non
385
starch polysaccharides such as AX stabilize protein foam against thermal disruption by virtue
386
of their enhanced viscosity which improves both the dough aqueous phase and the stability of
387
the liquid films surrounding gas cells (Izydorcyk et al., 1991; Prasad Rao et al., 2007).
388
Therefore, the rheological behavior of batters produced with the composite flour containing
389
6% MFAX showed higher viscosities at higher shear rates, which improved both specific
390
bread volume and crumb texture.
391
According to the established levels of MFAX and water, the flour containing 6% MFAX
392
blended with 105% water yielded the best quality GF breads (Table 2). These breads had 20%
393
higher specific volume and 14% softer structure with respect to the predicted values from the
394
optimized formulation by response surface methodology. With respect to control GF bread,
395
substitution of 6% on GF flour improved 20% and 33% the specific volume and crumb
396
texture respectively.
397
The functionality of MFAX on GF batter and bread quality is related to the functionality of
398
hydrocolloids. HMPC is one of the most suitable hydrocolloids to improve the volume and
399
texture on rice-based GF breads (Marco and Rosell, 2008). When compared to previous
400
studies, the best GF bread in the present study had higher specific volume compared to rice-
401
based GF breads supplemented with hydrocolloids (Lazaridou et al., 2007). The authors
402
obtained the highest specific volume with 1% β-glucan (2.68 mL/g) and 1% CMC (2.67
403
mL/g). Marco and Rosell (2008) documented specific volume of 2.71 mL/g for rice-based GF
404
breads containing 2% HPMC. Concerning to bread texture, the values were not compared
405
directly due to the differences in TPA conditions and probe. However, breads containing 2%
406
HPMC had 75% lower crumb hardness values compared to control counterparts (Marco and
407
Rosell, 2008). The same authors reported that breads supplemented with soybean protein
408
isolate (13%) and HPMC (2%) had 66% higher hardness even tough batters were produced
409
with 110% water absorption.
410
The development of GF bread with high quality and comparable to wheat bread represents a
411
challenge. The addition of 6% MFAX to the GF flour made possible to develop leavened GF
412
bread with a specific volume that represented 78% of the value reported by Chávez-Santoscoy
413
et al., (2016) in yeast-leavened whole wheat breads (4.37 mL/g).
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4.4.
Conclusions
From viscoamylograph analyses, it was confirmed that the smaller amounts of starch due to
416
the addition of MFAX to composite GF flours decreased both the starch peak viscosity and
417
retrogradation. According to response surface methodology, laccase did not have significant
418
effects on batter rheology and bread quality. However, the level of MFAX supplemented to
419
the GF composite flour and the water absorption levels greatly affected batter rheology and
420
bread quality. As expected, higher levels of water addition decreased batter consistency,
421
which improved both the bread specific volume and crumb texture. Likewise, breads had
422
softer crumb texture during 3 days of storage at room temperature. The adjustment of water
423
addition according to the selected consistency index allowed the optimization of the bread
424
formulations containing different levels of MFAX. This natural polymer of soluble fiber acted
425
as hydrocolloid improving water absorption and batter rheology to yield breads with higher
426
specific volume, softer crumb texture and lower staling. The best gluten-free breads in terms
427
of specific volume, texture and overall quality comparable to wheat bread were obtained with
428
batters containing 6% MFAX and higher amounts of water absorption (105%). These breads
429
contained the highest amounts of dietary fiber (approximately 1g total fiber/30g bread); and
430
more importantly, approximately 84% of this dietary fiber contribution was soluble. Acknowledgment
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The authors wish to acknowledge the support of the Nutriomic research chair (CAT-005)
433
from Tecnológico de Monterrey, México. Fabiola Ayala-Soto would like to thank CONACyT
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(scholarship number 285529) for the PhD financial support.
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4.6.
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Ayala-Soto, F. E., Campanella, O. H., Serna-Saldívar, S.S., Welti-Chanes, J. (2016). Changes in the structure and gelling properties of maize fiber arabinoxylans after their pilot scale extraction and spray-drying. Journal of Cereal Science, 70, 275-281.
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arabinoxylan preparations on baking properties of rye flour. Journal of Cereal Science
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Hemalatha, M. S., Manohar, R. S., Salimath, P. V. (2013). Effect of added arabinoxylans isolated from good and poor chapatti making wheat varieties on rheological properties of
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Lazaridou, A., Duta, D., Papageorgiou, M., Belc, N., Biliaderis, C.G., 2007. Effects of
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Marco, C., Rosell, C.M., 2008. Breadmaking performance of protein enriches, gluten-free breads. European Journal of Food Research Technology 227, 1205-1213.
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Mansberger, A., D’Amico, S., Novalin, S., Schmidt, J., Tömösközi, S., Berghofer, E.,
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Schoenlechner, R., 2014. Pentosan extraction from rye bran on pilot scale for application
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McCarthy, D.F., Gallagher, E., Gormley, T.R., Schoeber, T.J., Arendt, E.K., 2005.
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wheat flour on the gelatinization and gelation of wheat starches. Food Hydrocolloids 14
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exploiting variation in amount and composition to develop enhanced varieties. Journal of
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Schoeber, T.J., Messerschmidt, M., Bean, S.R., Park, S-H., Arendt, E.K. 2005. Gluten-free
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bread from sorghum: Quality differences among hybrids. Cereal Chemistry 82(4), 394–
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Storck, C.R., Zavareze, E.R., Guluarte, A., Cardoso Elias, M., Guerra Dias, A.R., 2013.
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Protein enrichment and its effects on gluten-free bread characteristics. Food Science and
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ACCEPTED MANUSCRIPT Title Table
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Table 1. Box-Behnken experimental design with different amounts of maize fiber
535
arabinoxylans, laccase and water absorptions for the development of gluten-free breads.
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Table 2. Rheological parameters of gluten-free batters produced from flours with different
537
MFAX levels and optimized water absorptions, and physical parameters of their respective
538
breads.
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Figure Captions
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Figure 1. Viscoamylographs of gluten free flours supplemented with 3% or 6% MFAX.
543
Figure 2. Response surface plots of the effects of MFAX, laccase and water absorption on
544
specific volume and hardness of GF breads.
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Figure 3. Viscosity rheograms of control and experimental batters containing 3% or 6%
546
MFAX with various water absorption levels.
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Figure 4. Effect of MFAX addition on yeast-leavened GF bread quality.
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ACCEPTED MANUSCRIPT Table 1. Water Absorption (%)
3%
2
90
3%
2
6%
1
3%
1
0%
1
6%
1
6%
0
3%
1
95
3%
0
90
1
90
0
95
6%
2
95
3%
1
95
3%
0
100
0%
2
95
100 90 95
100 100 95
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0%
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0%
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MFAX
Laccase enzyme (U activity/g flour)
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The amounts of maize fiber arabinoxylans (MFAX) are expressed as the percentage of substitution on composite GF flour. Water absorptions are expressed as mL water/100 g the composite GF flour
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Table 2.
98.27 ± 4.24 a
0.35 ± 0.02 c
47.65% ± 0.15% b
101.66 ± 3.89 a
0.42 ± 0.01 b
50.78% ± 1.24% ab
6% MFAX in flour
107.51 ± 2.35 a
0.54 ± 0.01 a
(105% water absorption)
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* Water percentage on flour basis
Day 3
51.79% ± 0.71% a
Crumb hardness (N) Day 0
Day 3
2.83 ± 0.09 b
45.79 ± 2.75 a
74.53 ± 4.70 a
47.28% ± 0.10% ab
3.05 ± 0.07 ab
42.36 ± 2.35 a
63.74 ± 1.47 ab
49.08% ± 0.62% a
3.41 ± 0.12 a
27.06 ± 1.86 b
50.80 ± 3.43 b
45.97% ± 0.25% b
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(100% water absorption)
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3% MFAX in flour
Day 0
Specific volume (mL/g)
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n
Control (95% water absorption)
Moisture content
K (Pa sn)
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Sample
GF breads
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GF batter
Fabiola E. Ayala-Soto, Sergio O. Serna-Saldívar, Jorge Welti-Chanes PII:
S0733-5210(16)30414-3
DOI:
10.1016/j.jcs.2016.11.003
Reference:
YJCRS 2240
To appear in:
Journal of Cereal Science
Received Date:
02 June 2016
Revised Date:
13 October 2016
Accepted Date:
07 November 2016
Please cite this article as: Fabiola E. Ayala-Soto, Sergio O. Serna-Saldívar, Jorge Welti-Chanes, Effect of arabinoxylans and laccase on batter rheology and quality of yeast-leavened gluten-free breads, Journal of Cereal Science (2016), doi: 10.1016/j.jcs.2016.11.003
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ACCEPTED MANUSCRIPT Highlights
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Maize fiber arabinoxylans (MFAX) decreased RVA peak viscosity in gluten free (GF) flour. MFAX addition decreased final RVA viscosity or retrogradation in GF flour. MFAX increased water absorption and benefited bread texture and volume. Laccase did not affect batter rheology nor GF bread quality.
ACCEPTED MANUSCRIPT 1
Effect of arabinoxylans and laccase on batter rheology and quality of yeast-leavened
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gluten-free breads
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Fabiola E. Ayala-Sotoa, Sergio O. Serna-Saldívara*, Jorge Welti-Chanesa
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Tecnológico de Monterrey. Escuela de Ingeniería y Ciencias. Centro de Biotecnología-
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FEMSA. Av. Eugenio Garza Sada 2501 Sur, C.P. 64849 Monterrey, N. L. Méxicoa.
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*Corresponding
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Sergio O. Serna-Saldívar
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Tecnológico de Monterrey. Escuela de Ingeniería y Ciencias. Centro de Biotecnología-
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FEMSA.
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Av. Eugenio Garza Sada 2501 Sur, C.P. 64849 Monterrey, N. L. México.
25
Tel. +52 (81) 83284322;
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Fax. +52 (81) 83284262;
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e-mail:[email protected]
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author:
ACCEPTED MANUSCRIPT The supplementation effects of maize fiber arabinoxylans (MFAX, 0%-6%), laccase (0-2 U/g
30
flour) and water absorption level (90%-100%) on gluten-free (GF) batter rheology and bread
31
quality were analyzed. From viscoamylograph analysis, lower starch amount in GF flour due
32
to MFAX addition decreased peak viscosity and retrogradation. Surface response plots
33
showed that laccase did not have significant effect on GF batter rheology and bread quality,
34
whilst water was the most important variable. Higher levels of water absorption benefited
35
bread texture. Higher water level (>100 mL/100 g flour) was needed in the experimental
36
design to evaluate correctly the effect of 6% MFAX replacement on GF bread quality. Further
37
analyses were carried in order to adjust water absorption of batters according to their
38
consistency index (K≈100 Pa sn), resulting an optimal water absorptions of 95%, 100% and
39
105% for control flour and flours supplemented with 3% or 6% MFAX, respectively. Thus,
40
MFAX addition enhanced water-binding capacity of flour and yielded GF breads with higher
41
specific volume and softer crumb texture. These quality parameters were best rated with 6%
42
MFAX addition to flours. This research demonstrated the potential of MFAX to develop GF
43
breads with improved quality, when optimal water level is used.
44
Keywords: maize fiber arabinoxylans (MFAX), batter rheology, gluten-free (GF) bread,
45
response surface methodology (RSM). Introduction
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Bakery products are important staples for practically all consumers around the world. Wheat
48
is unique as a raw material for the production of yeast-leavened products such as breads and
49
pastries. However, there is a group of individuals that suffer conditions such as coeliac
50
disease, allergy, gluten ataxia and non-celiac gluten sensitivity. These disorders are triggered
51
by the consumption of prolamin fractions derived from wheat (gliadin), rye (secalin) or barley
52
(hordein) (Rosell et al., 2015). The only treatment to gluten related disorder consists on
53
gluten-free (GF) diet, in which food products must contain lower than 20 ppm of total gluten.
54
The absence of gluten produces technological problems in the production of baked goods. GF
55
doughs are more fluid than wheat doughs and closer in viscosity to cake batters due the lack
56
of a gluten network (Schoeber et al., 2005). Different gums or hydrocolloids are often
57
incorporated in different GF bread formulations to improve dough development and gas
58
retention through the increase in system viscosity, producing loaves with higher specific
59
volume, better crumb structure, overall acceptability and shelf life (Marco and Rosell, 2008,
60
McCarthy et al., 2005).
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ACCEPTED MANUSCRIPT It is known that minor constituents such as non-starch polysaccharides in wheat flour play a
62
relevant role in the bread making process (Biliaderis et al., 1995). AX are non-starch
63
polysaccharides from the endosperm cell walls, aleurone layer and the pericarp of cereal
64
grains. The structure is mainly constituted of a linear β-(1,4)-D-xylopyranose backbone and
65
L-arabinofuranose residues as side chains on O-2 and/or O-3. Some of the arabinose moieties
66
are ester-linked on O-5 positions to hydroxycinnamic acids (HCA) such as ferulic acid (FA)
67
and p-coumaric acid (p-CA) (Saulnier et al., 2007). AX are subdivided into water-extractable
68
(WEAX) and unextractable (WUAX) fractions. Previous studies have reported that WEAX
69
have significant effects on dough properties and quality bread parameters such as loaf volume,
70
crumb texture and staling characteristics; which may impact positively or negatively
71
depending on flour quality, water absorption level and experimental design (Biliaderis et al.,
72
1995; Courtin and Delcour, 2002; Hemalatha et al., 2013). The influence of this polymer has
73
been related to the enhancement of viscosity, water holding capacity and gelation especially
74
when oxidants such as laccase enzyme are employed (Courtin and Delcour, 1998). Moreover,
75
due to their nature as soluble fiber and the presence of ferulic acid in their structure, AX also
76
exert health benefits in controlling diabetes mellitus, cardiovascular disorders, improving
77
colon function, activity against some types of cancer and immunological disorders (Zhou et
78
al., 2010; Ogawa et al., 2011; Rose et al., 2010; Saeed et al., 2011).
79
Few previous studies have shown an insight of the potential application of AX from in GF
80
products (Mansberger et al., 2014). However, no evidence exists about the behavior of the
81
polymer extracts in the development and features of GF breads. Due to their interesting
82
functionalities in wheat or rye breads, AX may physically and nutritionally improve the
83
quality of GF batter and bread. The present study is the first showing the potential application
84
of MFAX for the improvement of the properties of GF breads. In order to evaluate the
85
technological application of AX on GF bread formulations, the present study was undertaken
86
to determine the viscoamylograph changes (related to starch retrogradation) of composite GF
87
flour supplemented with MFAX. Likewise, by response surface methodology it was assessed
88
the effects of MFAX, dough water absorption level and laccase activity on the rheology of GF
89
batters and quality of corresponding GF breads especially in terms of specific volume and
90
crumb hardness.
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4.2.
Materials and methods
4.2.1. Materials
ACCEPTED MANUSCRIPT Composite GF flours, chosen by preliminary studies, had the following formulation: 33% rice
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flour, 32% corn starch, 22% brown rice flour, 5% pregelatinized corn starch, 4% egg albumin
95
and 4% soy protein isolate, determined from technical information of ingredients. The
96
composite formulation contained 13.1% moisture, 12.06% protein, 0.98% lipids, 79.22% non-
97
fibrous carbohydrates and 1.10% crude fiber. Salt, sugar, dry yeast and corn oil were
98
purchased from the local market.
99
Spray-dried MFAX were extracted under alkaline conditions and characterized as reported by
100
Ayala-Soto et al., (2016). Triplicates of 100 g of maize fiber were suspended in 0.3 M sodium
101
hydroxide (1:15 w/v agitated at 150 rpm) during 6 h at 60°C by using a glass beaker (capacity
102
3 L) covered with aluminum foil. The temperature was controlled through a magnetic stirring
103
hot plate (Thermo Scientific, USA). Following, the suspension was centrifuged at 4500 g for
104
15 min at 20°C (IEC CL40R, Thermo Scientific, France) and the resulting supernatant
105
acidified to pH 4 with 3 N hydrochloric acid. The precipitated hemicellulose A was separated
106
through centrifugation (4500 g for 15 min at 20°C) and the acidified supernatant was mixed
107
with 96% ethanol (55% v/v) in order to enhance the precipitation of hemicellulose B. The
108
solution was allowed to precipitate at 4°C overnight. The ethanol supernatant was separated
109
using a peristaltic pump (mini-pump variable flow, Fisher Scientific, USA). A second
110
precipitation of the AX extract was performed with 55% ethanol to decrease the content of
111
ethanol soluble compounds in the extract. The content of ethanol in the precipitate was
112
evaporated using rotary evaporation under vacuum at 80 mbar at 55°C and 100 rpm
113
(Rotavapor R-220 Büchi, Switzerland). During this process water was added to decrease the
114
high viscosity of the extract. In preparation for spray, the solids of the AX solution was
115
adjusted to 2.9% ± 0.3% and were set with inlet and outlet temperatures of 190°C and 90°C,
116
respectively and a flow rate of 570 mL/h (Spray drier 311S YAMATO Scientific Co, Japan).
117
The MFAX polymer had a composition of 97.34% carbohydrates, 1.79% protein, 0.21%
118
lipids (expressed on dry weight basis); A/X 0.69; molecular weights of 811 kDa and 756 kDa,
119
with distributions of 12.18% and 87.89%; average hydrodynamic radius of 380.2 nm; and
120
1.5% of terminal xylose linked directly to the backbone. This value is related to the branching
121
degree of the structure and represents an extract with lower branching structure compared to
122
16% of terminal xylose previously reported by Rumpagaporn et al., (2015) in maize AX. The
123
thermostable laccase extracted from Pycnoorus sanguineus was provided by the Emerging
124
and Molecular Nutrition research chair of Tecnológico de Monterrey, México (Ramírez-
125
Cavazos et al., 2014).
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4.2.2. Viscoamylograph properties Two levels of MFAX were substituted at the rate of 3% or 6% to the composite GF flour. The
128
pasting properties of a control sample and experimental GF flours were determined with the
129
Rapid-Visco Analyser (RVA) (RVA 4500, Perten Instruments, USA). Concerning to sample
130
preparation, 2.64 g (dry weight basis) of flour samples were weighed directly into the
131
aluminum RVA canister, distilled water was added to a total weight of 28 g, and then contents
132
mixed. The RVA test profile used was the reported by Storck et al., (2013). The sample was
133
held at 50C for 1 min, heated to 95C at a rate of 12C/minute, held at 95C for 2.5 min,
134
cooled to 50C at a rate of -12C/minute, and held at 50C for 2.5 min. The rotational speed
135
of the paddle was maintained at 160 rpm throughout the assay, except during the first 10 s
136
when 960 rpm were applied in order to facilitate the blending of the solids with the water.
137
Peak viscosity, breakdown, final viscosity and setback (difference between final viscosity and
138
peak viscosity) were evaluated.
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4.2.3. Experimental design
Response surface methodology (RSM) was used to study the effects of MFAX, laccase
141
enzyme and water addition on parameters related to bread quality such as specific volume and
142
hardness throughout 3 days of storage at room temperature. After preliminary baking tests,
143
the upper and lower limits for these variables were established. A completely random Box-
144
Behnken design was used and the MFAX levels were 0%–6% of flour replacement, laccase 1-
145
2 U/g flour and water absorption level 90%–100% (mL water/100 g flour). Three central
146
points and 3 levels of each parameter were selected to perform 15 baking trials (Table 1) in
147
duplicates. The analyses of variance (ANOVA) were used to determine the lack of fit and the
148
significance of the linear, quadratic and interaction effects of the independent variables on the
149
dependent variables.
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GF batters of the experimental formulations were prepared adding the following ingredients
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(percentages calculated on wet flour basis): sugar (6%), salt (1.5%), corn oil (5%), diacetyl-
153
tartaric acid ester of monoglycerides (DATEM) (0.3%), and calcium propionate (0.3%). The
154
batters were covered with a plastic film in order to avoid loss of moisture and allowed to rest
155
for 20 min. Shear viscosities were measured immediately afterwards at 25°C using a
156
rotational rheometer (Anton Paar, Austria) equipped with the parallel plates geometry (25 mm,
157
gap 1mm). The steady shear viscosity was determined (Kate et al., 2010) from 1 to 100 s-1 and
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the power law model (τ= Kγn) was used to describe the effect of shear rate on the viscosity of
159
the samples by determining the consistency index (K) as follow:
160
Log τ= n log γ + log K
161
Where: τ, shear stress; n, flow behavior index (dimensionless) that reflects the closeness to
162
Newtonian flow (n=1); γ, shear rate (s-1); and K, flow consistency index (Pa sn).
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(Eq. 1)
4.2.5. Breadmaking
A straight dough process was performed using a Kitchen-Aid professional mixer
165
(KSM150PSER, KitchenAid, St. Joseph, MI, USA) with a wire wipe (K45WW). The
166
following ingredients (percentages calculated on wet flour basis or bakers formulation) were
167
used: sunflower oil (5%), sucrose (6%), salt (1.5%), dry yeast (2%), yeast food (0.5%),
168
sodium propionate (0.3%) and DATEM (0.3%). The variables MFAX, laccase and water were
169
added according to the experimental design shown in Table 1. All ingredients were mixed for
170
5 min at speed 6 (in a scale 1–10 of the mixer). The batters were fermented for 30 min at
171
30°C and 90% relative humidity; then were weighted (24.39 g ± 0.04 g of solid content)
172
directly into non-stick mini loaf pan (25 x 55 x 100 mm) and fermented in a proofing chamber
173
at 30°C and 90% relative humidity for 30 additional min. After proofing, the batters were
174
baked (convection oven, Electrolux, USA) for 8 min at 195°C. Then the bread loaves were
175
removed from the pans, cooled for 60 min at room temperature, and packed in sealed
176
polyethylene bags to prevent dehydration.
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The loaf weight, bread height and volume were determined after 60 min of bread cooling. The
179
volume of each bread loaf was determined by rapeseed displacement. Specific volume (mL/g)
180
was obtained by dividing bread volume/bread weight. The moisture content of bread crumb
181
was determined by drying 3 g of sample in a forced convection oven at 105°C for 24 h. The
182
samples were cooled in desiccators and weighted. Three measurements of each sample were
183
performed.
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4.2.7. Texture analysis
185
Evaluation of crumb hardness of GF bread was performed the day 0 (3 hours after bread
186
making), and day 3. The loaves were stored in polyethylene bags at ambient temperature. The
187
crumb texture was determined using a TA-XT2 texture analyzer (Stable Microsystems, Surrey,
188
UK) with the ‘‘Texture Exponent’ software (Stable Micro Systems, England). A 60 mm
ACCEPTED MANUSCRIPT 189
diameter perspex compression probe was used in a ‘Texture Profile Analysis’ (TPA) double
190
compression test with 25% of strain, with a test speed of 5 mm/s, and a 5 s delay between the
191
first and second compressions. Hardness was calculated from the TPA plot. Measurements
192
were made on the central part of three slices (15 mm thickness) from breads of each batch. 4.2.8. Statistical analysis
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All analyses were done in triplicate and results expressed as mean ± standard deviations.
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Statistical analyses were conducted by one-way ANOVA, and differences among means were
196
compared with Tukey’s tests with a level of significance of P<0.05. Regression analyses,
197
Pearson’s correlations and main effect plots were performed to evaluate the relationship
198
between variables. Response surface plots were generated from the regression equations only
199
for significant interactions obtained by analysis of variance. All statistical analyses were
200
performed by using the JMP® Version 11 software (SAS Institute Inc., Cary, NC, USA).
201
4.3.
Results and discussion
4.3.1. Effect of MFAX substitution on pasting properties of gluten-free flour
203
It is known, that baking properties of starch depend mostly on its swelling and gelatinization
204
properties. The composite GF flour pasting properties would be useful to predict its
205
performance during processing and phenomenon of bread staling (Arif et al., 2012).
206
As shown in Figure 1, the supplementation of the two different levels of MFAX to the GF
207
flour significantly affected pasting properties. The substitution of 3% or 6% of MFAX (x)
208
correlated negatively (y= -0.105x + 2.07, R2= 0.96) with the average peak viscosity (y).
209
Values of control GF flour decreased from 2.1 Pa s to 1.68 Pa s (20.4% lower) and to 1.47 Pa
210
s (30% lower) with 3% and 6% of MFAX in flour, respectively. On the other hand, a positive
211
correlation existed between MFAX content (x) and the time (y) to achieve peak viscosity (y=
212
0.0889x + 5, R2=1). Compared to control GF flour, the replacement of 3% and 6% MFAX
213
increased the time to peak viscosity from 5 min to 5.27 min and 5.54 min, respectively. In fact,
214
the time increased 0.27 min with each 3% of MFAX substitution in the GF flour.
215
From regression analyses, negative correlations existed between the substitution level of
216
MFAX in GF flour (x) and the values of breakdown (y=- 0.06 x + 0.451, R2= 0.95) and final
217
viscosities (y) (y=-0.18 x + 3.28, R2=0.99). Breakdown viscosities in control GF flour exerted
218
the highest average value with 0.48 Pa s, followed by flours supplemented with 3% (0.23 Pa
219
s) or 6% MFAX (0.13 Pa s). High values of breakdown are associated with high peak
220
viscosities, which in turn, are related to the degree of swelling of the starch granules during
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ACCEPTED MANUSCRIPT heating (Arif et al., 2012). Final viscosity values of the control GF flour (3.29 Pa s) decreased
222
17.5% and 32.3% when 3 or 6% MFAX were added to the flour. Concerning to setback
223
viscosities (y), regression analysis showed quadratic correlations with the MFAX substitution
224
(x) level (y = 0.05 x2 – 0.39 x + 1.66, R² =1). The highest setback viscosity was observed in
225
the control GF flour (1.66 Pa s) whereas the lowest value was observed in the flour
226
supplemented with 3% MFAX (0.98 Pa s). The addition of 6% MFAX produced an
227
intermediate setback viscosity value of 1.27 Pa s.
228
The negative correlations of MFAX supplemented flours with peak, breakdown and final
229
viscosities, as well as the lower values of setback viscosity are attributed to the lower amount
230
of starch in flours and to the hydrophilic nature of MFAX that enhanced the binding of free
231
water which decreased the starch pasting properties. The time required to reach the peak
232
viscosity is an indirect measurement of the time required for cooking, and higher values are
233
related to the utilization of more energy to gelatinize the starch (Arif et al., 2012). The setback
234
is usually related to recrystallization of the amylose chains. Therefore, the addition of MFAX
235
and the lower starch amount weakened gelling of the GF flour likely decreasing granule
236
swelling and starch leaching, and thus decreased GF flour retrogradation, compared to control
237
sample.
238
Contradictory results related to the effects of AX on pasting properties of flours have been
239
previously published. Arif et al., (2012) reported a significantly reduced starch retrogradation
240
in white spring wheat flour due to the lower peak and setback viscosities as affected by the
241
addition of water-soluble pentosans. However, Sasaki et al., (2000) documented that the
242
addition of non-starch polysaccharides increased the peak and breakdown viscosities of wheat
243
flour. The discrepancies in results could be due to the different sources from which pentosans
244
were isolated and the quality of flour samples analyzed (Arif et al., 2012). In the present study,
245
it was utilized water soluble MFAX with high molecular weight (756 kDa-811 kDa) and low
246
degree of branching, compared with previous studies conducted by Rumpagaporn et al.,
247
(2015). It is known that high molecular AX with low branching structures exhibit higher
248
water solubility compared to counterparts with lower molecular weight and higher structure
249
complexity (Saulnier et al., 2007).
250 251
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4.3.2. Effect of MFAX, laccase and water absorption levels on gluten-free batter rheology
ACCEPTED MANUSCRIPT According to rheograms obtained (not shown here), which related shear stresses vs shear rates,
253
all the experimental GF batters showed shear thinning behavior with n values lower than 1
254
(n= 0.37 to 0.56), and coefficient of determination R2 close to 0.99 (Eq. 1). The consistency
255
index (k), which gives an indication of the viscosity of the fluid, varied from 77 Pa sn to 276
256
Pa sn. According to statistical analyses, both the MFAX addition and water absorption levels
257
significantly (P<0.05) affected K values whereas addition of laccase did not significantly
258
affect this parameter. The consistency index in GF batters increased at higher concentrations
259
of MFAX in flour and decreased at higher water absorption levels. The results agree with
260
previous investigations, which have demonstrated that AX increased viscosity and thus
261
affected functional properties (Courtin and Delcour, 1998; Saeed et al., 2011; Saulnier et al.,
262
2007).
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4.3.3. Effect of MFAX, laccase and water absorption levels on GF bread quality
The widely accepted quality criteria for breads are large volume, soft crumb, and a uniform
265
crumb grain. The selected parameters to evaluate the effect of MFAX, laccase and water
266
amount on quality of GF bread were specific volume and crumb texture or hardness.
267
The variable laccase and the interactions MFAX-laccase and laccase-laccase did not have
268
significant effects (P>0.05) on specific bread volumes. As shown in response surface plots of
269
Figure 2, higher values of specific volume were obtained when MFAX substitution ranged
270
from 1% to 3% in GF flour, and when the water absorption levels varied from 96 to 99%. The
271
lowest values were observed in breads supplemented with 6% MFAX produced with a water
272
absorption level of 90%. The results agreed with the study of Biliaderis et al., (1995) who
273
concluded that the relationship between preparation level and bread volume had a maximum
274
at certain amount of AX. Addition of 2% AX did not always yield breads with higher volume
275
compared to counterparts which only contained 1% of AX (Biliaderis et al., 1995). Mancebo
276
et al., (2015) reported similar results with the addition of HPMC to rice-based GF breads.
277
They stated that the effect of hydrocolloids depend of dough hydration, which increased
278
proportionally when the amount of hydrocolloid augmented. Probably the consistency of
279
batters with high level of MFAX was too thick which reduced the expansion of the carbon
280
dioxide produced by the yeast during proofing and baking consequently generating breads
281
with lower specific volumes. Renzetti et al., (2010) documented that increased batter
282
deformability was related to higher specific volumes of GF breads.
283
The bread hardness values after 3 days post baking were used for response surface analysis.
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ACCEPTED MANUSCRIPT The water absorption level and the interaction water absorption-MFAX were the parameters
285
that affected the most (P<0.05). From surface response plots, lower crumb hardness values
286
were associated to GF bread formulations with higher water absorptions (Figure 2). The
287
higher water absorption levels in breads have been previously related to texture improvement
288
in gluten-free formulations (de la Hera et al., 2014). Water acts as plasticizer lowering rigidity
289
in bakery items (Biliaderis et al., 1995). Unlike to specific volume, the substitution of 6%
290
MFAX improved the texture of GF breads when produced with water absorptions higher than
291
95%. The positive effects of MFAX on texture of GF breads could be due to their strong
292
water binding capacity that decreases starch gelatinization (as shown on viscoamylograph
293
analysis), stabilizes water and decreases the rate of moisture loss, which have been related to
294
the decrease in crumb firmness or staling rate. Additionally, the capacity of AX to interfere in
295
the intermolecular associations of both amylopectin and amylose is other reported mechanism
296
that reduces bread staling (Courtin and Delcour, 2002).
297
Contradictory reports exist concerning to the impact of AX and laccase on bread quality.
298
Some of them stated that water-soluble pentosans improves dough rheology and finally results
299
in better crumb structure and larger loaf volume (Courtin and Delcour, 2002, Buksa et al.,
300
2013) whereas other (Biliaderis et al., 1995) concluded that the higher moisture content of the
301
AX-supplemented crumbs increased starch retrogradation by amylopectin recrystallization
302
and therefore bread staling. Biliaderis et al., (1995) also showed contradictory results of bread
303
staling by DSC and firmness measurements, and concluded that no single technique can
304
provide a complete view of all events related to these phenomena. Different starting materials
305
and isolation techniques for AX, as well as the polymer structure, different bread-making
306
recipes and procedures may be responsible of these differences (Courtin and Delcour, 1998).
307
Concerning to laccase, other investigations showed significant positive effects of the enzyme
308
on bread quality. In this research the addition of laccase did not influence batter rheology nor
309
improved bread quality. Flander et al., (2008) concluded that laccase had detrimental results
310
on specific volume and texture of oat bread. However, Renzetti et al., (2010) reported positive
311
results on oat bread. The microbial origin of laccase, the type of flour, AX supplementation
312
and water absorption used to produce breads might explain the contradictory results (Renzetti
313
et al., 2010). Likewise, the time of fermentation should be a key factor to control in order to
314
allow the laccase to enhance AX crosslinking. In the present research the batters were rested
315
only 25 min, and breads were manufactured following the straight dough process with only 1
316
hour of fermentation. According to previous studies, the used MFAX sample gelled after two
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ACCEPTED MANUSCRIPT 317
hours under the action of this enzyme (Ayala-Soto et al., 2016). Probably, for this reason in
318
the present research the enzyme did not have a significant effect in batter rheology and bread
319
quality.
320
4.3.4. Optimization of gluten-free bread formulations According to the established levels of each variable, the optimization of GF bread
322
formulations was performed to maximize the specific volume and minimize bread hardness
323
values after 3 days storage at room temperature. With a desirability of 0.86, the most
324
outstanding GF breads were produced with 3.6% MFAX, 0 U/g laccase and 100% water
325
absorption. The resulting bread had a specific volume of 2.79 mL/g and 58.74 N of hardness
326
after 3 days of storage. However, response surface plots indicated that the selected range of
327
water absorption was not enough to optimize bread specific volume and texture in
328
formulations containing 6% MFAX.
329
The correct adjustment of water absorption is very relevant for both batter consistency and
330
bread quality especially when formulations are supplemented with AX. As mentioned above,
331
the high water affinity of AX decreases the free water and increases the batter consistency or
332
viscosity. Haque and Morris (1994) mentioned previously that the central problem to resolve
333
for the development of acceptable GF breads consists in adjusting water content to achieve
334
the right consistency. For this reason, K values were determined in order to establish a
335
relationship between dough rheology and parameters related to bread quality such as specific
336
volume and crumb hardness after 3 days of storage. Low correlations resulted between K
337
values and the studied parameters. However, it was possible to detect that breads with the
338
lowest hardness values for each MFAX level had similar batter consistencies. For the control
339
GF flour, the lowest crumb hardness and relative acceptable specific volume (>2.75 mL/g)
340
were observed in breads produced with a water absorption level of 95% whereas for
341
counterparts supplemented with 3% MFAX were 5 units higher or 100%. Both batters had K
342
values of 98 Pa sn and 101.7 Pa sn, respectively. As expected, batters containing 6% MFAX
343
had higher K values (145-276 Pa sn) and needed more water in order to obtain similar
344
consistency values.
345
Given the findings, the next step consisted on water optimization for GF flour enriched with
346
6% MFAX. It was determined as the water absorption needed to form GF batters with K
347
values quite similar to the other samples. Rheograms indicated that this specific formulation
348
required 105% water absorption and produced batters with K values of 107.5 Pa sn. Marco
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ACCEPTED MANUSCRIPT and Rosell (2008) used higher water level (110%) when producing GF rice flour-based breads.
350
Rheological analyses and breads were baked after determining the optimum water absorption
351
levels for the 3 different samples. Laccase was not considered because previous baking trials
352
clearly indicated that it did not improve batter nor bread properties. Table 2 depicts the
353
adjusted K values and the significant differences found for the n parameter for control and the
354
two experimental MFAX supplemented samples. High correlation existed between the water
355
absorption of the batters and n values (r= 0.98). In other words, the higher water addition
356
formed batters with lower shear thinning values and it was independent of the MFAX
357
concentration in flours. For example, the 6% MFAX flour mixed with the highest water
358
absorption (105%) formed batters with n values closer to 1. On the other hand, batters
359
containing 6% MFAX in flour were more resilient to decrease viscosity through the increase
360
of shear rate regardless of the water amount (Figure 3). The presence of MFAX in flour might
361
increase the entanglement between the polymer and ingredients forming a batter with higher
362
resistance to flow through the increase of shear rate.
363
Concerning to the corresponding GF breads, higher water absorption in batters formed breads
364
with higher moisture content and lower water losses (r=97) (Table 2). It is known that there is
365
an acceleration of the retrogradation rate with increasing moisture, especially in the range of
366
20%-45% water content (Biliaderis et al., 1995). In the present study, the moisture content
367
was higher than the cited range. As expected, the control bread contained the lowest moisture
368
whereas the counterpart containing 6% MFAX contained the highest moisture (Table 2).
369
After 3 days of storage, the control GF bread had the lowest moisture loss (1.67%), followed
370
by GF breads produced from formulations containing 6% MFAX (2.72%) and 3% MFAX
371
(3.50%). Despite the water losses, the GF breads with the highest level of MFAX had the
372
softest crumb being 1.7 and 1.5 times lower than control bread at days 0 and 3, whereas the
373
bread containing the lowest level of MFAX did not differ compared to the control bread
374
(Table 2). After 3 days, the control bread had the highest hardness (28.73 N), followed by
375
counterparts with the highest (23.05 N) and lowest MFAX levels (21.38 N).
376
Unlike the predicted results from the Box-Behnken design, the adjustment of water
377
absorption with respect to K values in flour supplemented with 6% MFAX not only formed
378
breads with the softest texture but also with the highest specific volume (Table 2, Figure 4).
379
The selected consistency index value was enough to allow gas bubble to expand during
380
proofing and baking. Furthermore, the addition of water according to the K parameter allowed
381
the formation of breads with uniform crumb loci, especially in breads produced with the
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ACCEPTED MANUSCRIPT highest MFAX concentration. Among breads, the 3% MFAX breads comparatively contained
383
larger loci (Figure 4).
384
In addition to the known plasticizing effect of water, previous studies have reported that non
385
starch polysaccharides such as AX stabilize protein foam against thermal disruption by virtue
386
of their enhanced viscosity which improves both the dough aqueous phase and the stability of
387
the liquid films surrounding gas cells (Izydorcyk et al., 1991; Prasad Rao et al., 2007).
388
Therefore, the rheological behavior of batters produced with the composite flour containing
389
6% MFAX showed higher viscosities at higher shear rates, which improved both specific
390
bread volume and crumb texture.
391
According to the established levels of MFAX and water, the flour containing 6% MFAX
392
blended with 105% water yielded the best quality GF breads (Table 2). These breads had 20%
393
higher specific volume and 14% softer structure with respect to the predicted values from the
394
optimized formulation by response surface methodology. With respect to control GF bread,
395
substitution of 6% on GF flour improved 20% and 33% the specific volume and crumb
396
texture respectively.
397
The functionality of MFAX on GF batter and bread quality is related to the functionality of
398
hydrocolloids. HMPC is one of the most suitable hydrocolloids to improve the volume and
399
texture on rice-based GF breads (Marco and Rosell, 2008). When compared to previous
400
studies, the best GF bread in the present study had higher specific volume compared to rice-
401
based GF breads supplemented with hydrocolloids (Lazaridou et al., 2007). The authors
402
obtained the highest specific volume with 1% β-glucan (2.68 mL/g) and 1% CMC (2.67
403
mL/g). Marco and Rosell (2008) documented specific volume of 2.71 mL/g for rice-based GF
404
breads containing 2% HPMC. Concerning to bread texture, the values were not compared
405
directly due to the differences in TPA conditions and probe. However, breads containing 2%
406
HPMC had 75% lower crumb hardness values compared to control counterparts (Marco and
407
Rosell, 2008). The same authors reported that breads supplemented with soybean protein
408
isolate (13%) and HPMC (2%) had 66% higher hardness even tough batters were produced
409
with 110% water absorption.
410
The development of GF bread with high quality and comparable to wheat bread represents a
411
challenge. The addition of 6% MFAX to the GF flour made possible to develop leavened GF
412
bread with a specific volume that represented 78% of the value reported by Chávez-Santoscoy
413
et al., (2016) in yeast-leavened whole wheat breads (4.37 mL/g).
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4.4.
Conclusions
From viscoamylograph analyses, it was confirmed that the smaller amounts of starch due to
416
the addition of MFAX to composite GF flours decreased both the starch peak viscosity and
417
retrogradation. According to response surface methodology, laccase did not have significant
418
effects on batter rheology and bread quality. However, the level of MFAX supplemented to
419
the GF composite flour and the water absorption levels greatly affected batter rheology and
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bread quality. As expected, higher levels of water addition decreased batter consistency,
421
which improved both the bread specific volume and crumb texture. Likewise, breads had
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softer crumb texture during 3 days of storage at room temperature. The adjustment of water
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addition according to the selected consistency index allowed the optimization of the bread
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formulations containing different levels of MFAX. This natural polymer of soluble fiber acted
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as hydrocolloid improving water absorption and batter rheology to yield breads with higher
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specific volume, softer crumb texture and lower staling. The best gluten-free breads in terms
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of specific volume, texture and overall quality comparable to wheat bread were obtained with
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batters containing 6% MFAX and higher amounts of water absorption (105%). These breads
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contained the highest amounts of dietary fiber (approximately 1g total fiber/30g bread); and
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more importantly, approximately 84% of this dietary fiber contribution was soluble. Acknowledgment
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4.5.
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The authors wish to acknowledge the support of the Nutriomic research chair (CAT-005)
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from Tecnológico de Monterrey, México. Fabiola Ayala-Soto would like to thank CONACyT
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(scholarship number 285529) for the PhD financial support.
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4.6.
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ACCEPTED MANUSCRIPT Title Table
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Table 1. Box-Behnken experimental design with different amounts of maize fiber
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arabinoxylans, laccase and water absorptions for the development of gluten-free breads.
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Table 2. Rheological parameters of gluten-free batters produced from flours with different
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MFAX levels and optimized water absorptions, and physical parameters of their respective
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breads.
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Figure Captions
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Figure 1. Viscoamylographs of gluten free flours supplemented with 3% or 6% MFAX.
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Figure 2. Response surface plots of the effects of MFAX, laccase and water absorption on
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specific volume and hardness of GF breads.
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Figure 3. Viscosity rheograms of control and experimental batters containing 3% or 6%
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MFAX with various water absorption levels.
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Figure 4. Effect of MFAX addition on yeast-leavened GF bread quality.
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ACCEPTED MANUSCRIPT Table 1. Water Absorption (%)
3%
2
90
3%
2
6%
1
3%
1
0%
1
6%
1
6%
0
3%
1
95
3%
0
90
1
90
0
95
6%
2
95
3%
1
95
3%
0
100
0%
2
95
100 90 95
100 100 95
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PT
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0%
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0%
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MFAX
Laccase enzyme (U activity/g flour)
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The amounts of maize fiber arabinoxylans (MFAX) are expressed as the percentage of substitution on composite GF flour. Water absorptions are expressed as mL water/100 g the composite GF flour
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Table 2.
98.27 ± 4.24 a
0.35 ± 0.02 c
47.65% ± 0.15% b
101.66 ± 3.89 a
0.42 ± 0.01 b
50.78% ± 1.24% ab
6% MFAX in flour
107.51 ± 2.35 a
0.54 ± 0.01 a
(105% water absorption)
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* Water percentage on flour basis
Day 3
51.79% ± 0.71% a
Crumb hardness (N) Day 0
Day 3
2.83 ± 0.09 b
45.79 ± 2.75 a
74.53 ± 4.70 a
47.28% ± 0.10% ab
3.05 ± 0.07 ab
42.36 ± 2.35 a
63.74 ± 1.47 ab
49.08% ± 0.62% a
3.41 ± 0.12 a
27.06 ± 1.86 b
50.80 ± 3.43 b
45.97% ± 0.25% b
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(100% water absorption)
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3% MFAX in flour
Day 0
Specific volume (mL/g)
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n
Control (95% water absorption)
Moisture content
K (Pa sn)
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Sample
GF breads
SC
GF batter