The microstructure and gas retention of bread dough

The influence of water-soluble arabinoxylan on the rheological properties of model dough and the interfacial properties of imitation dough liquor

Imitation dough liquor was formulated from natural dough liquid phase components, primarily comprising water-soluble arabinoxylan and wheat-soluble protein. It was found that arabinoxylan limited the diffusion rate of actively adsorbing components (Kdiff: -0.134 mNm-1 s-0.5 to -0.0573 mNm-1 s-0.5) and decreased the zeta potential (10.91 ± 1.31 mV to 5.76 ± 0.27 mV), which enhanced the composite viscosity and exhibited viscous properties in the low shear rate range. Model dough viscoelasticity decreased while rigidity improved with rising arabinoxylan ratios and critical thresholds existed (1:1.5 wheat, 1:2 potato). Arabinoxylan-enriched dough exhibited elevated tanδ values during thermal processing, enhancing ductility and plasticity compared to controls. The "film-like" shaped structure observed in the dough cavity contributes to maintaining the stability of the air-water interface, which in turn affects the rheological properties of the dough. This research establishes foundations for improving high fiber, low glycemic index fermented products.

Impact of compositionally diverse cereal flour water extracts on the gas cell size distribution and extensional rheology of model gluten-starch doughs

The role of water-extractable (WE) cereal flour constituents, and particularly WE proteins, in determining bread dough gas cell stability and bread specific volume (SV) remains ill-understood. We investigated the impact of compositionally diverse cereal flour aqueous extracts on bread SV, dough extensional rheology, and dough gas cell size distribution. To this end, aqueous extracts from wheat, rye, and defatted oat flours were either used as such, or their composition was modified by dialyzing out (i) low molecular mass constituents or (ii) both low molecular mass constituents and enzymatically hydrolyzed carbohydrates. These modifications generated wheat, rye, and oat extracts with increasing protein purities. Incorporating wheat or rye extracts in model gluten-starch (GS) doughs increased bread SV by 12-18%, regardless of modification, suggesting that not WE carbohydrates but probably proteins drive this effect. Dough extensional rheology and gas cell size distribution data could not explain these bread SV increases. It is hypothesized that wheat/rye WE proteins stabilize gas cells in dough by adsorbing at their interfaces. Incorporating oat extracts in GS dough led to a 50% decrease in bread SV. This was associated with oat extract-containing doughs having a lower strain hardening index, a lower gas cell number density, and a more heterogeneous gas cell size distribution. That similar effects were observed irrespective of the modification type suggests that oat WE proteins may be responsible for the adverse impact on dough and bread properties. Future efforts will focus on investigating direct gas cell stabilization effects by WE cereal flour constituents.

Alkali-Induced Protein Structural, Foaming, and Air-Water Interfacial Property Changes and Quantitative Proteomic Analysis of Buckwheat Sourdough Liquor

In this study, the protein structural, foaming, and air-water interfacial properties in dough liquor (DL) ultracentrifugated from buckwheat sourdough with different concentrations of an alkali (1.0-2.5% of sodium bicarbonate) were investigated. Results showed that the alkali led to the cross-linking of protein disulfide bonds through the oxidation of free sulfhydryl groups in DL. The alterations in protein secondary and tertiary structures revealed that the alkali caused the proteins in DL to fold, decreased the hydrophobicity, and led to a less flexible but compact structure. The alkali accelerated the diffusion of proteins and decreased the surface tension of DL. In addition, the alkali notably improved the foam stability by up to 34.08% at 2.5% concentration, mainly by increasing the net charge, reducing the bubble size, and strengthening the viscoelasticity of interfacial protein films. Quantitative proteomic analysis showed that histones and puroindolines of wheat and 13S globulin of buckwheat were closely related to the changes in the alkali-induced foaming properties. This study sheds light on the mechanism of alkali-induced improvement in gas cell stabilization and the buckwheat sourdough steamed bread quality from the aspect of the liquid lamella.

The potential of almonds, hazelnuts, and walnuts SFE-CO2 extracts as sources of bread flavouring ingredients

Nuts have been part of the human diet since our early ancestors, and their use goes beyond nutritional purposes, for example, as aromatic sources for dairy products. This work explores the potential of almond (Prunus dulcis (Mill.) DA Webb), hazelnut (Corylus avellana L.), and walnut (Juglans regia L.) extracts as sources of food flavouring agents, suggesting a new added-value application for lower quality or excess production fruits. The extracts were obtained by supercritical fluid extraction with carbon dioxide and characterized by: quantification of the volatile fraction by HS-SPME GC-MS; sensory perception and description; and cytotoxicity against Vero cells. All extracts revealed potential as flavouring ingredients due to terpene abundance. No significant differences were observed for the minimal sensory perception, in which the odour threshold values ranged from 8.3 × 10^-4 to 6.9 × 10^-3 μg·mL^-1 for walnuts and almonds extracts, respectively. In contrast, the cytotoxic potential differed significantly among the extracts, and P. dulcis extract presented lower cytotoxicity. Notes as woody, fresh, and green were identified in the volatile intensifiers obtained from the P. dulcis extract. Thus, almond extract was identified as the most promising ingredient to increase the sensory value of food products, namely bread. This potential was verified by an increase in the odour perception of bread after adding 4 μL of extract to each 100 g of bread dough. The quantified eucalyptol and d-limonene terpenes - found in the P. dulcis extract - have improved the release of the pleasant and natural volatile compounds from bread crust and crumb compared to the control bread chemical and sensory profiles.

Influence of blend proportion and baking conditions on the quality attributes of wheat, orange-fleshed sweet potato and pumpkin composite flour dough and bread: optimization of processing factors

Orange-fleshed sweet potato (OFSP) and pumpkin fruit are underutilized crops with great potential for the production of high-quality bread with health-enhancing properties. However, the incorporation of nonconventional flour in bread formula may influence the dough and bread quality properties. This study investigated the effect of partial substitution of wheat flour with OFSP (10–50%) and pumpkin flour (10–40%), baking temperature (150–200 °C) and baking time (15–25 min) on the quality properties of the composite dough and bread using response surface methodology (RSM). Dough rheological, bread physical and textural properties were analyzed, modelled and optimized using RSM. Satisfactory regression models were developed for the dough and bread quality attributes (R2 > 0.98). The dough development time, crust redness, hardness, and chewiness values increased while optimum water absorption of dough, specific volume, lightness, springiness, and resilience of bread decreased significantly (p < 0.05) with increasing incorporation of OFSP and pumpkin flour in the bread formula. Additionally, the specific volume, crust redness, crumb hardness, and chewiness of the composite bread increased significantly (p < 0.05) with increasing baking temperature from 150 to 180 °C but reduced at higher baking temperatures (≥ 190 °C). The staling rate declined with increased OFSP and pumpkin flour whereas increasing the baking temperature and time increased the bread staling rate. The optimized formula for the composite bread was 78.5% wheat flour, 11.5% OFSP flour, 10.0% pumpkin flour, and baking conditions of 160 °C for 20 min. The result of the study has potential applications in the bakery industry for the development of functional bread.

Graphical Abstract

Towards Sustainable Shifts to Healthy Diets and Food Security in Sub-Saharan Africa with Climate-Resilient Crops in Bread-Type Products: A Food System Analysis

Massive urbanization and increasing disposable incomes favor a rapid transition in diets and lifestyle in sub-Saharan Africa (SSA). As a result, the SSA population is becoming increasingly vulnerable to the double burden of malnutrition and obesity. This, combined with the increasing pressure to produce sufficient food and provide employment for this growing population together with the threat of climate change-induced declining crop yields, requires urgent sustainable solutions. Can an increase in the cultivation of climate-resilient crops (CRCs) and their utilization to produce attractive, convenient and nutritious bread products contribute to climate change adaptation and healthy and sustainable diets? A food system analysis of the bread food value chain in SSA indicates that replacement of refined, mostly imported, wheat in attractive bread products could (1) improve food and nutrition security, (2) bring about a shift to more nutritionally balanced diets, (3) increase economic inclusiveness and equitable benefits, and (4) improve sustainability and resilience of the food system. The food system analysis also provided systematic insight into the challenges and hurdles that need to be overcome to increase the availability, affordability and uptake of CRCs. Proposed interventions include improving the agronomic yield of CRCs, food product technology, raising consumer awareness and directing policies. Overall, integrated programs involving all stakeholders in the food system are needed.

Gas cell stabilization by aqueous-phase constituents during bread production from wheat and rye dough and oat batter: Dough or batter liquor as model system

Proper gas cell stability during fermentation and baking is essential to obtain high-quality bread. Gas cells in wheat dough are stabilized by the gluten network formed during kneading and, from the moment this network locally ruptures, by liquid films containing nonstarch polysaccharides (NSPs) and surface-active proteins and lipids. Dough liquor (DL), the supernatant after ultracentrifugation of dough, is a model system for these liquid films and has been extensively studied mostly in the context of wheat bread making. Nonwheat breads are often of lower quality (loaf volume and crumb structure) than wheat breads because their doughs/batters lack a viscoelastic wheat gluten network. Therefore, gas cell stabilization by liquid film constituents may be more important in nonwheat than in wheat bread making. This manuscript aims to review the knowledge on DL/batter liquor (BL) and its relevance for studying gas cell stabilization in wheat and nonwheat (rye and oat) bread making. To this end, the unit operations in wheat, rye, and oat bread making are described with emphasis on gas incorporation and gas cell (de)stabilization. A discussion of the knowledge on the recoveries and chemical structures of proteins, lipids, and NSPs in DLs/BLs is provided and key findings of studies dealing with foaming and air-water interfacial properties of DL/BL are discussed. Next, the extent to which DL/BL functionality can be related to bread properties is addressed. Finally, the extent to which DL/BL is a representative model system for the aqueous phase of dough/batter is discussed and related to knowledge gaps and further research opportunities.

Water Absorption Capacity Determines the Functionality of Vital Gluten Related to Specific Bread Volume

Vital gluten is often used in baking to supplement weak wheat flours and improve their baking quality. Even with the same recipe, variable final bread volumes are common, because the functionality differs between vital gluten samples also from the same manufacturer. To understand why, the protein composition of ten vital gluten samples was investigated as well as their performance in a microbaking test depending on the water content in the dough. The gluten content and composition as well the content of free thiols and disulfide bonds of the samples were similar and not related to the specific bread volumes obtained using two dough systems, one based on a baking mixture and one based on a weak wheat flour. Variations of water addition showed that an optimal specific volume of 1.74–2.38 mL/g (baking mixture) and 4.25–5.49 mL/g (weak wheat flour) was reached for each vital gluten sample depending on its specific water absorption capacity.

Development of “New” Bread and Cheese

Bread and cheese have been a popular combination since early times. Indeed, the history of bread dates back to 8000 BC and that of cheese to 7200 BC. However, new types of breads and cheeses are increasingly popular for several reasons, such as allergies, lifestyles, economy and religion. The major challenge is that food manufacturers are offering new products most of which are not welcomed by consumers. Therefore, recently, researchers have placed importance on their relationships with consumers to boost the success of new products. This short review summarizes the backgrounds of recent trends, processes, and principles to manufacture new bread and cheese products, and discusses future perspectives. The development of additive-free, gluten-free rice bread we have recently done from basic research to commercialization of the products is highly focused in this review. Additionally, ongoing studies on plant-based cheeses are introduced from material selection to suggest future outlooks.

Effect of microbial exopolysaccharide on wheat bran sourdough: Rheological, thermal and microstructural characteristics

Rheological, thermal and microstructural properties of wheat bran sourdough (WBS) containing different levels of microbial exopolysaccharide (EPS) extracted from Lactobacillus plantarum were investigated. All sourdough samples showed pseudoplastic behavior and the highest apparent viscosity was achieved at 1.5% EPS. The values of consistency coefficient of 1 and 2.5% EPS were significantly lower than for the dough without EPS. Increasing EPS in WBS produced a decrease in the storage, loss, and complex moduli of the sourdough, except that made with 1.5% EPS. This can be attributed to the microbial EPS structure and its ability to bind with water. It can be concluded, due to high hygroscopicity of EPS, WBS containing EPS had a lower access to water and other dough constituents. Thermal and microstructural results showed that EPS strongly modified starch gelatinization by prohibiting water access to amorphous parts of the granules and stabilized crystalline regions of starch causing an increase of end set temperature.

Volume, firmness and crumb characteristics of gluten-free bread based on extruded quinoa flour and lactic acid

Abstract Coeliac disease forces on the developing of gluten-free products. Gluten-free cereals may be modified by techniques like cooking-extrusion or by adding compounds like lactic acid in order to obtain mixtures with adequate viscoelastic properties for the developing of baked products. The present work studies the elaboration of gluten-free bread with extruded quinoa (Chenopodium quinoa Willd) flour and lactic acid. The influence of feeding humidity (18% and 25%) and temperature of extrusion (60 °C and 95 °C) on water absorption index (WAI) and water solubility index (WSI) of extruded flours was investigated. The results showed that feeding humidity led to changes on WAI. Baking process was studied by varying the amount of lactic acid added during bread baking. The specific volume, firmness and crumb characteristics (average cell size and cell number per mm2) of bread were determined. A control sample based on commercial gluten-free flour and no lactic acid was used. The results showed that lactic acid content did not affect bread firmness. Bread prepared with extruded flours at 95 °C, 25% feeding moisture had higher firmness (p < 0.05) than bread prepared with other extruded flours and control sample. Low level of lactic acid (0.2%) led to bread with high specific volume. The use of an extruded quinoa flour with low levels of lactic acid led to a gluten-free bread with a high specific volume and low firmness.

Recent practical researches in the development of gluten-free breads

Wheat bread is consumed globally and has played a critical role in the story of civilization since the development of agriculture. While the aroma and flavor of this staple food continue to delight and satisfy most people, some individuals have a specific allergy to wheat or a genetic disposition to celiac disease. To improve the quality of life of these patients from a dietary standpoint, food-processing researchers have been seeking to develop high-quality gluten-free bread. As the quality of wheat breads depends largely on the viscoelastic properties of gluten, various ingredients have been employed to simulate its effects, such as hydrocolloids, transglutaminase, and proteases. Recent attempts have included the use of redox regulation as well as particle-stabilized foam. In this short review, we introduce the ongoing advancements in the development of gluten-free bread, by our laboratory as well as others, focusing mainly on rice-based breads. The social and scientific contexts of these efforts are also mentioned.

Influence of dextran synthesized in situ on the rheological, technological and nutritional properties of whole grain pearl millet bread

The effect of dextran produced in situ by Weissella confusa on the structure and nutrition quality of whole grain pearl millet bread containing 50% of wheat flour was investigated. NMR spectroscopy analysis indicated that the dextran formed by the strain consisted of a α-(1 → 6)-linked linear backbone and 3% α-(1 → 3) branches, and had a molar mass of 3.3 × 10⁶ g/mol. In situ production resulted in 3.5% dextran (DW) which significantly enhanced the dough extensional properties, increased the bread specific volume (∼13%) and decreased crumb firmness (∼43%), moisture loss (∼15%) and staling rate (∼10%), compared to the control millet bread. DSC analysis showed that amylopectin recrystallization was significantly reduced in the bread containing dextran. In situ dextran production altered the nutritional value of millet, leading to increased free phenolic content (∼30%) and antioxidant activity. It also markedly lowered the bread predicted glycemic index and improved in vitro protein digestibility.

Wheat (Triticum aestivum L.) flour free lipid fractions negatively impact the quality of sponge cake

The functionality of wheat flour lipids in sponge cakes prepared from flour, sugar, eggs and leavening agents only was investigated by altering their location or content in flour. Hexane (hex) or the more polar hexane:isopropanol (3:2 v/v) (hex:isoprop) were used to impact free flour lipid (FFL) or both FFL and bound flour lipid (BFL) fractions, respectively. Flour from which the FFLs were removed resulted in significantly improved cake volumes and crumb structures. Additional removal of part of the BFLs did not further impact cake quality. Prior contact of flour with hex:isoprop followed by gently removing the solvent broke native interactions between BFLs and starch or gluten and relocated more lipids than did hex. Cakes from flour with relocated lipids had coarse crumb structures. Our study demonstrates that FFLs and relocated flour lipids negatively impact sponge cake quality by disturbing air-liquid interface stabilization during mixing and the early phases of baking.

Relating the composition and air/water interfacial properties of wheat, rye, barley, and oat dough liquor

Gas cell stabilization in dough by its aqueous phase constituents is arguably more important in non-wheat than in wheat dough due to weaker protein networks in the former. Dough liquor (DL), a model for the dough aqueous phase, was isolated from fermented wheat, rye, barley, and oat doughs by ultracentrifugation. DL composition (protein, lipid, arabinoxylan, β-glucan) and air/water interfacial functionality [foaming, viscosity, surface tension, surface dilatational modulus (E)] were related to bread quality. Poor foaming and low E of wheat DL were ascribed to lipids and proteins co-occurring at the interface. Nonetheless, the presence of a gluten network resulted in high-quality wheaten breads. Homogeneous and heterogeneous crumb structures of rye and barley breads, respectively, were attributed to high and low E values of their respective DLs. High lipid content and low surface tension of oat DL indicated a lipid-dominated interface, which may explain the heterogeneous crumb structure of oat breads.

Flour quality and disproportionation of bubbles in bread doughs

The bread making process transforms wheat flour doughs into highly porous breads. Bread has been shown (Wang, Austin and Bell, 2011) to be a single, open cell that is massively interconnected giving it a maze-like structure that encompasses the entire volume. The solid strands are also porous and contain closed cells. How the bubbles in dough mix partition into these open and closed cells in bread is not known. This study was undertaken to track changes in bubbles in doughs using 3-D X-ray microtomography techniques as doughs proofed and were baked. The mechanical properties of doughs were measured to establish how dough rheology impacted bubble growth. The doughs were made with 'medium strong' Canadian flour (CWRS) and 'weak' Australian flours (Wylk). Both doughs had similar protein amounts and strain-hardening characteristics; however the CWRS dough was more elastic. The scans identified formation of clusters of partially-coalesced bubbles from which one cluster grew to form a massively interconnected, single, closed cell in doughs as doughs proofed. Microscopy studies confirmed that the open cell in breads was made of partially-coalesced bubbles. Compared to the dough made with the Australian flours, the dough made from Canadian flour had a thicker dough layer separating bubbles, smaller size bubbles and a slower rate of formation of the continuous structure. This study highlights the critical role of dough elasticity and the disproportionation phenomena of bubble growth in controlling the quality of cell structures in dough and baked products.

Wheat (Triticum aestivum L. and T. turgidum L. ssp. durum) Kernel Hardness: II. Implications for End-Product Quality and Role of Puroindolines Therein

 Wheat kernel hardness is a major quality characteristic used in classifying wheat cultivars. Differences in endosperm texture among Triticum aestivum L. or between T. aestivum and T. turgidum L. ssp. durum cultivars profoundly affect their milling behavior, the properties of the obtained flour or semolina particles, as well as the quality of products made thereof. It is now widely accepted that the presence, sequence polymorphism, or absence of the basic and cysteine-rich puroindolines a and b are responsible for differences in endosperm texture. These proteins show features in vitro, including foaming and lipid-binding properties, which provide them with a potential impact in the production of wheat-based food products, where they may improve gas cell stabilization or modulate interactions between starch, proteins, and/or lipids. We here summarize the impact of wheat hardness on milling properties and bread, cookie, cake, and pasta quality and discuss the role of puroindolines therein.

Substituting normal and waxy-type whole wheat flour on dough and baking properties

Normal (cv. Keumkang, KK) and waxy-type (cv. Shinmichal, SMC) whole wheat flour was substituted at 20 and 40% for white wheat flour (WF) during bread dough formulation. The flour blends were subjected to dough and baking property measurement in terms of particle size distribution, dough mixing, bread loaf volume and crumb firmness. The particle size of white wheat flour was the finest, with increasing coarseness as the level of whole wheat flour increased. Substitution of whole wheat flour decreased pasting viscosity, showing all RVA parameters were the lowest in SMC40 composite flour. Water absorption was slightly higher with 40% whole wheat flour regardless of whether the wheat was normal or waxy. An increased mixing time was observed when higher levels of KK flour were substituted, but the opposite reaction occurred when SMC flour was substituted at the same levels. Bread loaf volume was lower in breads containing a whole wheat flour substitution compared to bread containing only white wheat flour. No significant difference in bread loaf volume was observed between normal and waxy whole flour, but the bread crumb firmness was significantly lower in breads containing waxy flour. The results of these studies indicate that up to 40% whole wheat flour substitution could be considered a practical option with respect to functional qualities. Also, replacing waxy whole flour has a positive effect on bread formulation over normal whole wheat flour in terms of improving softness and glutinous texture.

Effect of water migration between arabinoxylans and gluten on baking quality of whole wheat bread detected by magnetic resonance imaging (MRI)

A new method, a magnetic resonance imaging (MRI) technique characterized by T(2) relaxation time, was developed to study the water migration mechanism between arabinoxylan (AX) gels and gluten matrix in a whole wheat dough (WWD) system prepared from whole wheat flour (WWF) of different particle sizes. The water sequestration of AX gels in wheat bran was verified by the bran fortification test. The evaluations of baking quality of whole wheat bread (WWB) made from WWF with different particle sizes were performed by using SEM, FT-IR, and RP-HPLC techniques. Results showed that the WWB made from WWF of average particle size of 96.99 μm had better baking quality than those of the breads made from WWF of two other particle sizes, 50.21 and 235.40 μm. T(2) relaxation time testing indicated that the decreased particle size of WWF increased the water absorption of AX gels, which led to water migration from the gluten network to the AX gels and resulted in inferior baking quality of WWB.

Moisture-pressure combination treatments for cyanide reduction in grated cassava

Several cyanide-associated health disorders have been linked with frequent consumption of mildly toxic cassava (Manihot esculenta crantz) products in individuals on a low-protein diet. Production of bread from cassava often involves application of prolonged physical pressure (pressing) to the freshly grated root for several hours. This study aimed to determine effects of pressure and wetting on grated cassava. Six treatments were applied: confining pressure for 12 h, wetting for 4 h at 25 °C, 2 h at 25 °C, 2 h at 40 °C, and 2 h at 50 °C, or each of the above followed by pressure for 12 h. Treatments released cyanide from samples in the order: 2-h wet at 50 °C + pressing >4-h wet at 25 °C + pressing = 2-h wet at 40 °C + pressing >2-h wet at 25 °C + pressing = 4-h wet at 25 °C >12-h pressing. Wetting for 2 h at 50 °C followed by pressure for 12 h reduced cyanide levels by at least 20% more than that of any other treatment. The combination of moisture and pressure enhanced the contact time between linamarin and linamarase to increase the release of hydrogen cyanide.