Effect of Sourdough and α-amylase on qualitative properties of toast bread

The quality of breads depends on the baking capability of flour, fermentation time, protein content, and type of additives. An economically important concern of the baking industry is delayingthe bread staling. In addition, the staling process changes outer and inner properties, scent, flavor, and chewiness of breads, which in turn leads to staled or, in other words, non-fresh breads. The application of lactic sourdough and/or other techniques such as improved dough making, improved baking quality, packaging, and use of additives and improvers can be highly effective in delaying this process. One of the additives that improve the properties of baked products is the α-amylase enzyme. α- amylase can improve the elastic properties of the texture while delaying staling. This enzyme can also form useful sugars for yeasts and increase gas formation in dough, which in turn improves and increases the bread volume. Against this background, the current study analyzed the effects of sourdough and α-amylase on qualitative characteristics, physicochemical properties, staleness, size and sensory profile of the toast breads.
The ingredients of the toast bread dough, i.e. 78% wheat flour (1 kg), sugare (1-2 w/w%), salt (1.8-2.2%), oil (3-6%), yeast (1.5-2%), α-amylase (0.01-0.03%), lactic sourdough (4 and 6% of wheat weight), were prepared and weighed to make the dough required for the baking process. The dough samples were spread and then rolled after an initial resting of 10-15 minutes. The rolls (approx. 580 g) were transferred to a cast. The dough samples were finally moved to the fermentation chamber at 35°C and 80% relative humidity for final fermentation and baking. Their analyzed using different physical, chemical, and sensory tests. A completely randomized design with three replications was used to analyze experimental data (except for staleness data of bread samples from sensory and instrumental tests which were analyzed using factorial experiment with a completely randomized design). Means were compared by Duncan's multiple-range test (α = 1%) in SPSS 16.
According to the results, α-amylase and lactic sourdough caused an increase in bread’s MC compared to the control samples. In other words, starch hydrolysis by α-amylase created free water in the dough. Moreover, sourdough increased water absorption of wheat through mechanisms including production of exopolysaccharides and increased production of pentosans. The application of α-amylase and lactic sourdough also increased the ash content of the breads compared to the control samples because they increased the production of dextrins and synthesis of exopolysaccharides. It should be mentioned that these additives decreased the pH of breads compared to the control samples. This is because the sourdough bacteria produced lactic, acetic and other acids that acidified the medium and reduced the pH. This enzyme also produced metabolites like dextrins and increased the amount of fermented active ingredients, which further reduced the pH. The proteolytic activity of lactic bacteria of the acid in sourdough led to decomposition of proteins, particularly gluten, into amino acids. This also reduced the protein content and diluted the gluten in breads. The results showed that the lactic acid bacteria of the sourdough hydrolyzed the fat control of bread samples by their lipase and thus lowered the fat content in bread samples compared to the control. The fiber content of samples was higher than that in the control as a result of enzyme and sourdough application. This is due to the fact that fermentation increases the pentosan content and reduces their molecular size. It also increased solubility of insoluble fibers like beta-glucans. On the other hand, their application led to larger bread size than the control because α-amylase hydrolyzes the starch and breaks the amylose and amylopectin chains to convert them into disaccharide substrates. Accordingly, yeasts could grow better and produce more CO2 in the dough, increasing the bread size. The application of this enzyme and lactic sourdough gave a brighter appearance to toast bread samples whereas a* and b* were reduced. This is because the bread undergoes changes in its crust color during the baking process, which are mainly caused by maillard and caramelization reactions. It is worth noting that these additives reduced the staleness of the samples. With respect to staling, the gluten content and its ratio to starch are highly effective. During the bread shelf life, as its kinetic energy decreases, the cross-linking increases and intensities. In other words, the bread becomes harder and staler. However, using α-amylase and sourdough, the bread hardness and staleness are decreased as the starch swelling is limited and cross-linking between protein and gluten is inhibited. These two additives improved most sensory properties including resistance to breakage and rupture, porosity, kernel color, crumb color, proportionality of shape, back-side uniformity, flavor, taste, texture, chewiness, and larger size of the bread samples. This reason for these improvements can be due to starch hydrolysis by α-amylase and production of dextrins and CO2. According to the results, the bread sample containing 0.03% α-amylase and 6% lactic sourdough was selected as the best sample.