Dough and bread made from high- and low-protein flours by vacuum mixing: Part 2. Yeast activity,dough proofing and bread quality

The combined effects of reduced mixer headspace pressure and mixing duration on the yeast activity, proofing and quality of dough and bread made from both high-protein flour (HPF) and low-protein flour (LPF) were addressed in this study. Rheofermentometer analysis showed that a reduction in mixer headspace pressure up to 0.08 MPa did not affect the overall gassing power of yeast in either of the two dough matrices. An increase in mixing duration sped up the mass transfer rate of CO₂ at the initial stage of fermentation, leading to a faster expansion of dough volume at the beginning. Moreover, an increase in mixing time promoted dough development and gas inclusion, which resulted in a increased volume of dough and bread, as well as a softer texture of both baked bread and steamed bread. In general, reduced headspace pressure produced baked bread of smaller volume, denser structure and harder texture. On the other hand, vacuum mixing produced steamed bread with softer texture without significantly changing the bread’s volume and porosity.     

Volume and texture improvement of gluten-free bread using quinoa white flour

Patients suffering from coeliac disease have to avoid traditional cereals-based products and depend on the availability of gluten-free alternatives. The gluten-free bread matrix and its foam stability are strongly affected by the choice of ingredients. In this study, the impact of quinoa white flour on bread quality parameters, in particular volume, has been investigated. The pseudocereal proved to be a suitable substrate for dough aeration using yeast, since considerably more glucose and a higher activity of α-glucosidase were found in comparison to rice and corn flour. Consequently, quinoa white flour was used to replace 40–100% of the rice and corn flour in a gluten-free control recipe. As a result, quinoa white flour enhanced the specific volume by 33%, which was related to the absence of bran components and the increased α-glucosidase activity. The significance of the latter was proven by separately adding sucrose and fungal amyloglucosidase to the control recipe. Moreover, the crumb featured homogeneous and finely distributed gas bubbles and the taste was not compromised. Thus, it was possible to improve the quality of gluten-free bread by using quinoa white flour, which might be a relief for coeliac patients.     

Improved viscoelastic zein–starch doughs for leavened gluten-free breads: Their rheology and microstructure

Gluten-free bread was prepared from commercial zein (20 g), maize starch (80 g), water (75 g), saccharose, NaCl and dry yeast by mixing above zein's glass transition temperature (T_g) at 40°C. Addition of hydroxypropyl methylcellulose (HPMC, 2 g) significantly improved quality, and the resulting bread resembled wheat bread having a regular, fine crumb grain, a round top and good aeration (specific volume 3.2 ml/g). In model studies, HPMC stabilized gas bubbles well. Additionally, laser scanning confocal microscopy (LSCM) revealed finer zein strands in the dough when HPMC was present, while dynamic oscillatory tests showed that HPMC rendered gluten-like hydrated zein above its T_g softer (i.e. |G*| was significantly lower). LSCM revealed that cooling below T_g alone did not destroy the zein strands; however, upon mechanical impact below T_g, they shattered into small pieces. When such dough was heated above T_g and then remixed, zein strands did not reform, and this dough lacked resistance in uniaxial extension tests. When within the breadmaking process, dough was cooled below T_g and subsequently reheated, breads had large void spaces under the crust. Likely, expanding gas bubbles broke zein strands below T_g resulting in structural weakness.     

Rheofermentometer parameters and bread specific volume of frozen sweet dough influenced by ingredients and dough mixing temperature

Response surface methodology described the effects of salt, lactic acid, shortening, and exogenous trehalose and dough mixing temperature (DMT) and their interactions on the three rheological and fermentation parameters. These included maximum dough height (Hm), maximum height of gas release (Hm′) and CO₂ production, measured by the Rheofermentometer F3, and bread specific volume (Sp. Vol.) of frozen sweet dough. The models could estimate the four parameters with R² values of 0.76, 0.69, 0.93, and 0.59, respectively. Salt significantly influenced all four parameters in a negative way. DMT affected positively the Hm and Sp. Vol. of bread. Lactic acid affected Hm only, but its interactions with other variables influenced all four parameters. Shortening level affected Hm′ and CO₂ production positively and Sp. Vol. negatively. The added exogenous trehalose improved Hm, Hm′, and CO₂ production significantly, but not the Sp. Vol. of bread. Among the three Rheofermentometer parameters, Hm showed the highest correlation with Sp. Vol. (R² = 0.75). DMT for the maximum Hm and Sp. Vol. varied with the level of other ingredients. Trehalose alone could not overcome the challenges in a sweet frozen dough system to improve the Sp. Vol., and its combined effects with other ingredients will need to be evaluated to restore the impaired gas retention of the frozen sweet dough.     

Rheofermentometer parameters and bread specific volume of frozen sweet dough influenced by ingredients and dough mixing temperature

Response surface methodology described the effects of salt, lactic acid, shortening, and exogenous trehalose and dough mixing temperature (DMT) and their interactions on the three rheological and fermentation parameters. These included maximum dough height (Hm), maximum height of gas release (Hm′) and CO₂ production, measured by the Rheofermentometer F3, and bread specific volume (Sp. Vol.) of frozen sweet dough. The models could estimate the four parameters with R² values of 0.76, 0.69, 0.93, and 0.59, respectively. Salt significantly influenced all four parameters in a negative way. DMT affected positively the Hm and Sp. Vol. of bread. Lactic acid affected Hm only, but its interactions with other variables influenced all four parameters. Shortening level affected Hm′ and CO₂ production positively and Sp. Vol. negatively. The added exogenous trehalose improved Hm, Hm′, and CO₂ production significantly, but not the Sp. Vol. of bread. Among the three Rheofermentometer parameters, Hm showed the highest correlation with Sp. Vol. (R² = 0.75). DMT for the maximum Hm and Sp. Vol. varied with the level of other ingredients. Trehalose alone could not overcome the challenges in a sweet frozen dough system to improve the Sp. Vol., and its combined effects with other ingredients will need to be evaluated to restore the impaired gas retention of the frozen sweet dough.     

A novel approach for improving yeast viability and baking quality of frozen dough by adding biogenic ice nucleators from Erwinia herbicola

Freezing deteriorates the baking quality of frozen bread dough by causing lethal injury to yeast cells and depolymerization to the gluten network. To investigate the potential of biogenic ice nucleators in frozen food applications, the effect of extracellular ice nucleators (ECINs) from Erwinia herbicola on the baking quality of frozen dough upon three freeze/thaw cycles were investigated. With addition of ECINs to the activity of 2.4 × 10⁶ units per gram of dough, hardening of bread crumb caused by three freeze/thaw cycles was alleviated by about 50% compared to the control. Additionally, the bread from frozen dough with added ECINs showed 50% larger specific volume compared to the control. The mechanism of cryoprotective effects from ECINs was possibly that ECINs helped in preserving the viability of yeast cells during freeze/thaw cycles. ECINs were able to improve the viability of log-phase and stationary-phase yeast cells in suspensions by about 100 and 10 fold, respectively, and viability of yeast in the frozen dough by 17%. This study revealed the potential of ECINs as a cryoprotectant for applications in the food and biotechnology industries.     

Extensional rheological properties in mixed and fermented/rested dough and relationships with steamed bread quality

In this study, sixteen wheat varieties for cultivation in China were examined for the flour characteristics using the farinograph, extensograph and rheofermentometer, uniaxial extensional rheology employing the extensograph and the Kieffer extensibility rig and biaxial extension by uniaxial compression of mixed dough with and without yeast, rested and fermented dough, and steamed bread quality including specific volume and texture properties. Three statistical analysis methods including Pearson correlation, principle component and stepwise multiple regression analysis were carried out to correlate dough properties with steamed bread quality. Biaxial extension viscosity was positively correlated with texture properties (hardness and chewiness) of steamed bread (r = 0.521–0.685, p < 0.05). Based on the correlation coefficients and the model (r² = 0.852, p = 0.003) obtained using stepwise multiple regression analysis, the best predictors for specific volume of steamed bread were the maximum resistance to extension of rested dough (r = 0.664, p < 0.01) and total work for breakage of fermented dough (r = 0.662, p < 0.01). Principal component analysis of rheological properties of fermented dough and flour characteristics provided more useful information for discriminating wheat flour quality and help breeders to select most convenient wheat flour for the steamed bread making.     

Gluten-Free Breads and Cookies of Raw and Popped Amaranth Flours with Attractive Technological and Nutritional Qualities

Gluten-free bakery foodstuffs are a challenge for technologists and nutritionists since alternative ingredients used in their formulations have poor functional and nutritional properties. Therefore, gluten-free bread and cookies using raw and popped amaranth, a grain with high quality nutrients and promising functional properties, were formulated looking for the best combinations. The best formulation for bread included 60–70% popped amaranth flour and 30–40% raw amaranth flour which produced loaves with homogeneous crumb and higher specific volume (3.5 ml/g) than with other gluten-free breads. The best cookies recipe had 20% of popped amaranth flour and 13% of whole-grain popped amaranth. The expansion factor was similar to starch-based controls and the hardness was similar (10.88 N) to other gluten-free cookies. Gluten content of the final products was around 12 ppm. The functionality of amaranth-based doughs was acceptable although hydrocolloids were not added and the final gluten-free products had a high nutritional value.     

Aeration of bread dough influenced by different way of processing

The effect of steady shearing versus z-blade mixing on mechanical aeration and gas retaining ability of the dough during processing and subsequent proofing and bread baking stages was investigated. Reduction in moisture content led to reduction in both static and dynamic densities of z-blade mixed dough. At low moisture content, dough had higher consistency and tended to physically entrap more air bubbles upon processing, leading to a higher dough volume and, thereby a low density. The results showed that both processes led to similar mechanical aeration as measured by static dough density immediately after processing. Shearing at a low rotational speed, led to similar proofing dough volume as z-blade mixing did. Nevertheless, both dough expansion test and breadmaking trials showed a significant reduction in gas retaining ability of sheared dough, especially at higher rotational speeds. This is explained by the fact that higher shear rates could break up the gluten network and negatively influence gas retaining ability. The results revealed the influence of processing conditions; e.g. the type of deformation flow on dough aeration. Furthermore, it was shown that rotational speed in the shearing system influences the aeration and gas holding ability of the dough during proofing and baking processes.     

Improved viscoelastic zein–starch doughs for leavened gluten-free breads: Their rheology and microstructure

Gluten-free bread was prepared from commercial zein (20 g), maize starch (80 g), water (75 g), saccharose, NaCl and dry yeast by mixing above zein's glass transition temperature (T_g) at 40°C. Addition of hydroxypropyl methylcellulose (HPMC, 2 g) significantly improved quality, and the resulting bread resembled wheat bread having a regular, fine crumb grain, a round top and good aeration (specific volume 3.2 ml/g). In model studies, HPMC stabilized gas bubbles well. Additionally, laser scanning confocal microscopy (LSCM) revealed finer zein strands in the dough when HPMC was present, while dynamic oscillatory tests showed that HPMC rendered gluten-like hydrated zein above its T_g softer (i.e. |G*| was significantly lower). LSCM revealed that cooling below T_g alone did not destroy the zein strands; however, upon mechanical impact below T_g, they shattered into small pieces. When such dough was heated above T_g and then remixed, zein strands did not reform, and this dough lacked resistance in uniaxial extension tests. When within the breadmaking process, dough was cooled below T_g and subsequently reheated, breads had large void spaces under the crust. Likely, expanding gas bubbles broke zein strands below T_g resulting in structural weakness.     

Preparation of gluten-free bread using a meso-structured whey protein particle system

This article presents a novel method for making gluten-free bread using mesoscopically structured whey protein. The use of the meso-structured protein is based on the hypothesis that the gluten structure present in a developed wheat dough features a particle structure on a mesoscopic length scale (100 nm–100 μm). Whey protein particles were prepared by cold gelation of soluble whey protein aggregates during phase separation. The addition of a 2.4% whey protein particle suspension to wheat starch resulted in a dough that could be baked into a leavened bread with a specific volume up to 3.7 ml/g and a bubble size comparable with a normal bread. The relevance for structuring the whey protein into mesoscopic particles was confirmed by tests in which only a homogeneous whey protein gel or a whey protein solution was used. The protein particle system gave better results after proving and baking compared with these systems.     

Improvement to baking quality of frozen bread dough by novel zein-based ice nucleation films

Freezing deteriorates the baking quality of frozen bread dough. This study revealed the protective effects of zein-based ice nucleation films (INFs) on the baking quality of frozen dough. INFs were prepared by immobilizing biogenic ice nucleators on the surface of zein films, which consequently revealed ice nucleation activity and increased the ice nucleation temperature of water from −15 °C to −6.7 °C. By using these films to wrap frozen dough during five freeze/thaw cycles, the specific volume of bread was increased by up to 25% compared to the bread from control frozen dough. The reason was attributed to 40% more viable yeast cells preserved by INFs. In addition, zein-based INFs also reduced the water loss by frozen dough resulting in higher water content in bread crumb. Combining the protective effects on both specific volume and water content from zein-based INFs, the obtained bread showed 68% lower firmness and fracturability and 2.4 times higher resilience compared to the control. The INFs were also superior in that for zein-based INFs, biogenic ice nucleators showed desirable affinity with the surface to sustain at least fifteen repetitive uses on freezing water.     

Effect of the addition of extruded wheat flours on dough rheology and bread quality

Extruded wheat flours, due to their increased water absorption capacity, constitute an opportunity to increase bread output in bakery production. However extrusion may modify dough and bread characteristics. The aim of this study was to investigate the effect of the substitution of 5% of the wheat flour by extruded wheat flour (produced with different time-temperature extrusion treatments) on dough mixing, handling and fermentation behaviour and bread volume, shape, texture and colour. The RVA curves indicate that extrusion intensity increases with increasing temperature or water content. Water absorption capacity rises with increasing treatment intensity, but dough stability tends to decrease. Adding extruded flours decreases dough extensibility but increases tenacity and gas production. Differences in dough structure were observed on photomicrography, though there were no clear differences in bread quality. These results indicate that it is possible to obtain adequate dough and bread characteristics using dough with 5% extruded wheat flour.     

Optimisation of rheological properties of gluten-free doughs with HPMC,psyllium and different levels of water

Hydrocolloids have traditionally been investigated as an alternative to gluten for making good quality products for coeliac patients. This study investigated the interactions between hydroxypropylmethylcellulose (HPMC) (2–4 g/100 g of flour), psyllium (0–4 g/100 g of flour) and water level (90–110 g/100 g of flour) in gluten-free breadmaking. Psyllium incorporation reduced the pasting temperature and compliance values, and increased elastic (G′) and viscous (G″) moduli values. In contrast, HPMC addition had no important effects on pasting properties and compliance values, but also increased G′ and G″ values. Psyllium inclusion reduced bread specific volume and increased bread hardness, while there were hardly differences in the bread specific volume and hardness between the percentages of HPMC studied. In addition, when the dough hydration level was increased, there was a decrease in the influence of hydrocolloids on dough rheology and specific volume and hardness of breads.     

Comparison of the impact of dextran and reuteran on the quality of wheat sourdough bread

This study investigates the influence of in situ exopolysaccharides (EPS) and organic acids on dough rheology and wheat bread quality. Dextran forming Weissella cibaria MG1 was compared to reuteran forming Lactobacillus reuteri VIP. For in situ production of EPS, sourdoughs were supplemented with 15% sucrose. Control sourdoughs were prepared with the same strain but without sucrose. W. cibaria MG1 and L. reuteri VIP formed 5.1 and 5.8 g kg⁻¹ dextran and reuteran, respectively. Formation of EPS from sucrose led to production of high amounts of acetate by L. reuteri VIP, but only small amounts were detected in W. cibaria MG1 sourdough. EPS containing sourdough or control sourdough was incorporated at 10% and 20% in wheat dough. EPS significantly influenced the rheological properties of the dough, with dextran exhibiting the strongest impact. The addition of dextran enriched W. cibaria MG1 sourdough significantly increased CO₂ production, whereas increased acidity in reuteran containing dough reduced gas production. The quality of wheat bread was enhanced when 10% of L. reuteri-sucrose sourdough was added. The positive effect of reuteran was masked by increased acidification after 20% sourdough addition. Incorporation of dextran enriched sourdough (10% and 20%) provided mildly acidic wheat bread with improved bread quality.     

The relationship between rheological characteristics of gluten-free dough and the quality of biologically leavened bread

The rheological characteristics of gluten-free doughs and their effect on the quality of biologically leavened bread were studied in amaranth, chickpea, corn, millet, quinoa and rice flour. The rheological characteristics (resistance to extension R, extensibility E, R/E modulus, extension area, stress at the moment of dough rupture) were obtained by uniaxial dough deformation. Specific loaf volume of laboratory prepared gluten-free breads was in significant positive correlation with dough resistance (r = 0.86), dough extensibility (r = 0.98) and peak stress at the moment of dough rupture (r = 0.96). Even if the correlation between R/E modulus and the characteristics of loaf quality were not significant, the breads with the highest specific loaf volume were prepared from flours with R/E closer to the wheat check sample (18 N?mm-1). The results showed, in general, good baking flours exhibited stronger resistance to extension and greater extensibility, but differences found were not directly related to the results of baking tests.     

Evaluation of a new method to determine the water addition level in gluten-free bread systems

The water content in gluten-free recipes plays an essential role in the resulting product quality. Up to date the water adjustment is conducted mainly by trial-and-error. Brabender GmbH & Co. KG developed an attachment for the Farinograph, which makes the measurement of batter consistencies feasible. The water content was adjusted using this new tool and compared to the water determined based on the water hydration capacity (WHC) of the single bulking ingredients. Furthermore, bread quality characteristics were analysed. Five different hydrocolloids were tested in a gluten-free system based on rice flour. Water levels differed significantly, when guar gum (20% water) or sodium alginate (18% water) were incorporated. The use of Farinograph resulted generally in a higher specific volume (+0.63 ml/g) and a softer crumb (−16 N). On the contrary, the WHC-method only gave an indication about the water addition but did not consider temperature changes during mixing and its effect on the hydration. In conclusion, Farinograph can be considered as a useful tool for the determination of the optimal water content, and additionally provides useful information about batter stability and dough development time.     

Pilot scale production of a non-immunogenic soluble gluten by wheat flour transamidation with applications in food processing for celiac-susceptible people

Celiac disease (CD) is an immune-mediated disease triggered by wheat gluten and related prolamins. A lifelong gluten-free (GF) diet is mandatory to normalize the intestinal mucosa. We previously found that transamidation by microbial transglutaminase of gluten was effective in suppressing the gliadin-specific inflammatory response in CD patients without influencing the main technological properties of wheat flour or semolina. In this study, we produced on a pilot scale a soluble form of transamidated gluten (soluble protein fraction, spf), characterised by a high protein content (88 mg/ml), while native gluten was dramatically reduced (32 ± 2 ppm; R5-ELISA). Using HLA-DQ8 transgenic mice as a CD model, we found suppression of interferon-γ secretion in gliadin-specific CD4⁺ T cells challenged with spf-primed dendritic cells. In terms of functional properties, spf showed both solubility and emulsifying activity values within the range of commercial soluble glutens. Notably, dough prepared by mixing rice flour with spf could leaven. After baking, blended rice bread had a higher specific volume (2.9 ± 0.1) than control rice bread (2.0 ± 0.1) and acquired wheat-like sensory features. Taken together, our results highlighted the technological value of transamidated soluble gluten to improve both nutritional and sensory parameters of GF food.     

Measurement of dough specific volume in chemically leavened dough systems

Gas production and gas retention properties of doughs are pivotal to the manufacture of bread of good quality, but these properties are rarely measured directly in fermenting dough due to a paucity of suitable instrumentation. A digital image analysis-based method was used to measure the dynamic specific volume (DSV) of various chemically leavened dough systems. Sodium bicarbonate (1.4–4.2 g per 100 g of flour) in combination with equivalent neutralizing amounts of the leavening acidulants glucono-delta-lactone, potassium acid tartrate, adipic acid or sodium acid pyrophosphate consistently increased the specific volume of bread dough so that void fractions in the dough spanned between 5 and 67% at ordinary fermentation temperatures. The relationship between the specific volume of dough at the end of fermentation and the actual gas evolved (measured independently) was essentially linear and was characterized by a slope that provided a good index of the actual gas-trapping properties of dough. Therefore, the use of the DSV technique in conjunction with chemical leaveners offers the possibility of obtaining quantitative, real time information on the gassing capacity of the leavening system and the gas-holding capacity of the dough.     

Effect of extrusion cooking of sorghum flour on rheology,morphology and heating rate of sorghum–wheat composite dough

Addition of a gluten-free flour such as sorghum has negative impact on the quality of wheat dough for bread making. One of the methods which can be used to promote the quality of sorghum-wheat composite dough is to extrude the sorghum flour before incorporation. In this regard, to produce a dough with appropriate bakery properties sorghum flour was extruded at 110 °C and 160 °C die temperature with 10%, 14% and 18% feed moisture. The effect of extruded sorghum flour incorporation (10%) on rheological (farinography and stress relaxation behavior), morphological and temperature profile of sorghum-wheat composite dough were evaluated. Extrusion cooking altered the sorghum-wheat composite dough properties through partial gelatinization of starch granules. Addition of extruded sorghum flour increased the water absorption and dough development time but it decreased the dough stability. Native sorghum-wheat composite dough showed viscoelastic liquid-like behavior whereas addition of sorghum flour extrudate changed dough to a more viscoelastic solid-like structure. Maxwell model was more appropriate than Peleg model to describe the viscoelasticity of the sorghum-wheat composite dough. Extrusion cooking decreased composite dough elasticity and viscosity. Sorghum extrudate increased the heating rate of composite dough crumb during baking. Addition of extruded sorghum flour formed a non-uniform and less compact dough structure. As a result, dough containing extruded sorghum flour had a good potential for producing a high-yielding bread in a short time of baking.