Wheat Sourdough Breadmaking: A Scoping Review.

Using sourdough in breadmaking can enhance bread's shelf-life and flavor compared to exclusive baker's yeast use and is believed to increase its nutritional quality and healthiness. Previous research established insight into the microbial ecology of sourdough, but the link between leavening agent use, processing, and bread quality remains elusive. However, such knowledge is key for standardization, research on the health benefits, and the definition of sourdough bread. In this systematic scoping review, we analyzed 253 studies and identified large variations in the type and amount of leavening agent, fermentation conditions, and bread quality (specific loaf volume and acidification). The interrelation between these elements and their effect on the extent of fermentation is discussed, together with issues preventing proper comparison of breadmaking procedures. With this review, we want to contribute to the dialogue concerning the definition of sourdough-type bread products and the research into the health benefits attributed to them.

Impact of process parameters on the specific volume of wholemeal wheat bread made using sourdough- and baker's yeast-based leavening strategies.

The final quality of wholemeal wheat bread is determined by the process parameter settings and leavening strategy. We hypothesise that the used leavening strategy may influence the optimal process parameter settings and, as such, the specific volume of the bread loaf. To analyse this interaction, bread was leavened with (i) a type 1 sourdough (SB), (ii) a type 1 sourdough combined with baker's yeast (YSB), or (iii) baker's yeast (YB). For each leavening strategy, the specific volume of bread, in response to variations in mixing time (4-10/4-14 min), water absorption (60-85 %), and proofing time (1-7/1-3 h), was analysed using an I-optimal response surface experimental design. Data modelling identified a substantially lower maximal specific volume of SB (2.13 mL/g), compared to YSB (3.30 mL/g) and YB (3.26 mL/g). The proofing time and water absorption mostly influenced the specific volume of the SB and YSB, respectively. However, the mixing and proofing times mainly affected the specific volume of YB. The type 1 sourdough reduced the mixing time and water absorption required for an optimal specific volume of bread compared to baker's yeast. These results challenge the idea of yielding higher volumes upon using sourdough compared to baker's yeast and highlight the importance of optimisation of bread dough formulations and breadmaking processes.

Decreasing the Crystallinity and Degree of Polymerization of Cellulose Increases Its Susceptibility to Enzymatic Hydrolysis and Fermentation by Colon Microbiota.

Cellulose can be isolated from various raw materials and agricultural side streams and might help to reduce the dietary fiber gap in our diets. However, the physiological benefits of cellulose upon ingestion are limited beyond providing fecal bulk. It is barely fermented by the microbiota in the human colon due to its crystalline character and high degree of polymerization. These properties make cellulose inaccessible to microbial cellulolytic enzymes in the colon. In this study, amorphized and depolymerized cellulose samples with an average degree of polymerization of less than 100 anhydroglucose units and a crystallinity index below 30% were made from microcrystalline cellulose using mechanical treatment and acid hydrolysis. This amorphized and depolymerized cellulose showed enhanced digestibility by a cellulase enzyme blend. Furthermore, the samples were fermented more extensively in batch fermentations using pooled human fecal microbiota, with minimal fermentation degrees up to 45% and a more than eight-fold increase in short-chain fatty acid production. While this enhanced fermentation turned out to be highly dependent on the microbial composition of the fecal pool, the potential of engineering cellulose properties to increased physiological benefit was demonstrated.

The Wheat Starchy Endosperm Protein Gradient as a Function of Cultivar and N-fertilization Is Reflected in Mill Stream Protein Content and Composition.

Within the wheat starchy endosperm, the protein content increases biexponentially from the inner to outer endosperm. Here, we studied how this protein gradient is reflected in mill fractions using three cultivars (Claire, Apache, and Akteur) grown without and with N-fertilization (300 kg N ha-1). The increasing protein content in successive break fractions was shown to reflect the protein gradient within the starchy endosperm. The increasing protein content in successive reduction fractions was primarily due to more aleurone contamination and protein-rich material being harder to reduce in particle size. The miller's bran fractions had the highest protein content because of their high sub-aleurone and aleurone content. Additionally, the break fractions were used to deepen our understanding of the protein composition gradient. The gradient in relative gluten content, increasing from inner to outer endosperm, was more pronounced without N-fertilization than with and reached levels up to 87.3%. Regarding the gluten composition gradient, no consistent trends were observed over cultivars when N-fertilization was applied. This could, at least partly, explain why there is no consensus on the gluten composition gradient in the literature. This study aids millers in managing fluctuations in the functionality of specific flour streams, producing specialized flours, and coping with lower-quality wheat.

Decreasing the degree of polymerization of microcrystalline cellulose by mechanical impact and acid hydrolysis.

Depolymerization of cellulose is often used as a (pre)treatment protocol within the catalytic valorization strategies of cellulose. Typical depolymerization protocols yield polymerization degrees above 70 anhydroglucose units (AGU). However, shorter cellulose fibers are of interest in the search for accessible dietary fiber additives or renewable materials with distinct mechanical properties (bio-composites). In this work, short-polymer microcrystalline celluloses (SMCC) with an average polymerization degree between 29 and 70 AGU were produced with material yields of 95 % and above by combining a planetary ball mill pretreatment with mild acid hydrolysis. By first decreasing the levelling-off degree of polymerization (LODP) with an intensive ball mill treatment, a mild acid hydrolysis protocol was sufficient to ensure high yields of SMCC. Furthermore, the desired polymerization degree could be obtained by tuning the process parameters.

Process-Induced Changes in the Quantity and Characteristics of Grain Dietary Fiber.

Daily use of wholegrain foods is generally recommended due to strong epidemiological evidence of reduced risk of chronic diseases. Cereal grains, especially the bran part, have a high content of dietary fiber (DF). Cereal DF is an umbrella concept of heterogeneous polysaccharides of variable chemical composition and molecular weight, which are combined in a complex network in cereal cell walls. Cereal DF and its distinct components influence food digestion throughout the gastrointestinal tract and influence nutrient absorption and other physiological reactions. After repeated consumption of especially whole grain cereal foods, these effects manifest in well-demonstrated health benefits. As cereal DF is always consumed in the form of processed cereal food, it is important to know the effects of processing on DF to understand, safeguard and maximize these health effects. Endogenous and microbial enzymes, heat and mechanical energy during germination, fermentation, baking and extrusion destructurize the food and DF matrix and affect the quantity and properties of grain DF components: arabinoxylans (AX), beta-glucans, fructans and resistant starch (RS). Depolymerization is the most common change, leading to solubilization and loss of viscosity of DF polymers, which influences postprandial responses to food. Extensive hydrolysis may also remove oligosaccharides and change the colonic fermentability of DF. On the other hand, aggregation may also occur, leading to an increased amount of insoluble DF and the formation of RS. To understand the structure-function relationship of DF and to develop foods with targeted physiological benefits, it is important to invest in thorough characterization of DF present in processed cereal foods. Such understanding also demands collaborative work between food and nutritional sciences.

The Effect of Wet Milling and Cryogenic Milling on the Structure and Physicochemical Properties of Wheat Bran.

Wheat bran consumption is associated with several health benefits, but its incorporation into food products remains low because of sensory and technofunctional issues. Besides, its full beneficial potential is probably not achieved because of its recalcitrant nature and inaccessible structure. Particle size reduction can affect both technofunctional and nutrition-related properties. Therefore, in this study, wet milling and cryogenic milling, two techniques that showed potential for extreme particle size reduction, were used. The effect of the milling techniques, performed on laboratory and large scale, was evaluated on the structure and physicochemical properties of wheat bran. With a median particle size (d50) of 6 µm, the smallest particle size was achieved with cryogenic milling on a laboratory scale. Cryogenic milling on a large scale and wet milling on laboratory and large scale resulted in a particle size reduction to a d50 of 28-38 µm. In the milled samples, the wheat bran structure was broken down, and almost all cells were opened. Wet milling on laboratory and large scale resulted in bran with a more porous structure, a larger surface area and a higher capacity for binding water compared to cryogenic milling on a large scale. The extensive particle size reduction by cryogenic milling on a laboratory scale resulted in wheat bran with the highest surface area and strong water retention capacity. Endogenous enzyme activity and mechanical breakdown during the different milling procedures resulted in different extents of breakdown of starch, sucrose, ß-glucan, arabinoxylan and phytate. Therefore, the diverse impact of the milling techniques on the physicochemical properties of wheat bran could be used to target different technofunctional and health-related properties.

The impact of wheat (Triticum aestivum L.) bran on wheat starch gelatinization: A differential scanning calorimetry study.

The effect of wheat bran on starch gelatinization temperature was investigated. Dynamic water vapour sorption and water retention capacity experiments showed that bran bound up to 3 times more water than starch. However, examining starch gelatinization in starch-bran-water mixtures with differential scanning calorimetry showed that the effect of substituting starch by bran differed from that of moving into a regime of limiting water. Modelling the effect of the mixture composition on starch gelatinization behavior indicated that the onset (To) and peak (Tp) gelatinization temperatures were positively impacted by the bran concentration in water. The conclusion temperature (Tc) was negatively affected by the water content. Fractionation experiments demonstrated that the increased To and Tp were mainly caused by the extractable wheat bran components, such as potassium and phosphorus, which decrease the plasticization capacity of the solvent. The mechanism behind our observations was explained with the side-chain liquid-crystalline polymeric model for starch.

Extrusion-Cooking Modifies Physicochemical and Nutrition-Related Properties of Wheat Bran.

The potential of extrusion-cooking to change the physicochemical characteristics of wheat bran, increase its nutritional value and decrease its recalcitrance towards fermentation was investigated in this study. The conditions in a twin-screw extruder were varied by changing screw configuration, moisture content and barrel temperature. The former was not previously investigated in studies on bran extrusion. Extrusion-cooking resulted in an increased water-holding capacity and extract viscosity of bran, suggesting shear-induced structure degradation and structure loosening due to steam explosion at the extruder outlet. Modelling showed that the extent of these modifications mainly correlates with the amount of specific mechanical energy (SME) input, which increases with an increasing number of work sections in the screw configuration and a decreasing moisture content and barrel temperature. Extrusion led to solubilisation of arabinoxylan and ferulic acid. Moreover, it led to starch melting and phytate degradation. Upon fermentation of the most modified sample using a human faecal inoculum, small numeric pH decreases and short-chain fatty acid production increases were observed compared to the control bran, while protein fermentation was decreased. Overall, extrusion-cooking can improve the nutrition-related properties of wheat bran, making it an interesting technique for the modification of bran before further use or consumption as an extruded end product.

Assessing the impact of xylanase activity on the water distribution in wheat dough: A 1H NMR study.

The molecular mobility of water and biopolymers in wheat dough and the influence of xylanases thereon was investigated with time domain proton nuclear magnetic resonance relaxometry. To reduce the complexity, model systems containing starch, gluten and/or water-unextractable arabinoxylan (WU-AX) were used. In the starch-WU-AX-water model, starch binds water fast but less strong compared to WU-AX, resulting in water withdrawal from starch during resting. In contrary, WU-AX did not affect the water distribution in a gluten-WU-AX-water system, despite the higher water retention capacity (WRC) of WU-AX compared to gluten. In a starch-gluten-WU-AX-water model and in wheat flour, water was distributed over the different constituents including WU-AX. Addition of xylanase reduced the WRC of WU-AX, resulting in a release of water. Therefore, the beneficial effect of xylanase on dough and bread quality can, in part, be attributed to the redistribution of water, initially bound by WU-AX, between the other flour constituents.

Study into the effect of microfluidisation processing parameters on the physicochemical properties of wheat (Triticum aestivum L.) bran.

The physicochemical properties of wheat bran have an effect on its technofunctional and nutritional profile. The possibility to induce physicochemical modifications in wheat bran using microfluidisation was investigated. An I-optimal experimental design was used to investigate the effect of microfluidisation processing parameters (pressure, number of passes, bran concentration and initial particle size) on important properties of wheat bran (particle size, microstructure, chemical composition, water retention capacity (WRC), extractability, viscosity and sedimentation). With the parameters used in this study, microfluidisation reduced wheat bran median particle size to 14.8 µm and disintegrated starch granules from the attached endosperm. This coincided with an increased extractability of starch and arabinoxylan. While the initial particle size was of minor importance, a higher pressure, larger number of passes and lower bran concentration during microfluidisation resulted in a smaller particle size, higher WRC and extractability, and an increased viscosity and stability in a 2% wheat bran suspension.

Sensitivity of the Bacillus subtilis Xyn A Xylanase and Its Mutants to Different Xylanase Inhibitors Determines Their Activity Profile and Functionality during Bread Making.

The importance of inhibition sensitivity for xylanase functionality in bread making was investigated using mutants of the wild-type Bacillus subtilis xylanase (XBSTAXI), sensitive to Triticum aestivum xylanase inhibitor (TAXI). XBSNI, a mutant with reduced sensitivity to TAXI, and XBSTI, a mutant sensitive to all wheat endogenous proteinaceous inhibitors (TAXI, Xylanase Inhibiting Protein and Thaumatin-like Xylanase Inhibitor) were used. The higher inhibition sensitivity of XBSTAXI and XBSTI compared to XBSNI was associated with a respective 7- and 53-fold increase in enzyme dosage required for a maximal increase in bread loaf volume. XBSTI and XBSTAXI were only active during the mixing phase and the beginning of fermentation, while XBSNI was able to hydrolyze arabinoxylan until the end of fermentation. In spite of this difference in activity profile, no differences in loaf volume were observed for the different xylanases at optimal concentrations. Dough extensional viscosity analysis suggests that increased water availability as a result of xylanase activity favors starch-starch and starch-gluten interactions and drives the improvement in bread loaf volume.

Density separation as a strategy to reduce the enzyme load of preharvest sprouted wheat and enhance its bread making quality.

As preharvest sprouting of wheat impairs its use in food applications, postharvest solutions for this problem are required. Due to the high kernel to kernel variability in enzyme activity in a batch of sprouted wheat, the potential of eliminating severely sprouted kernels based on density differences in NaCl solutions was evaluated. Compared to higher density kernels, lower density kernels displayed higher α-amylase, endoxylanase, and peptidase activities as well as signs of (incipient) protein, ß-glucan and arabinoxylan breakdown. By discarding lower density kernels of mildly and severely sprouted wheat batches (11% and 16%, respectively), density separation increased flour FN of the batch from 280 to 345s and from 135 to 170s and increased RVA viscosity. This in turn improved dough handling, bread crumb texture and crust color. These data indicate that density separation is a powerful technique to increase the quality of a batch of sprouted wheat.