Studies On The Baking Properties Of Buckwheat Bread Fermented By Lactobacillus From Sourdough

In this study, five typical lactic acid bacteria(LABs) were screened from traditional sourdough: Lactobacillus plantarum(LP), Lactobacillus brevis(LB), Lactobacillus sanfrancisco(LS), Lactobacillus fermentum(LF) and Pediococcus pentosaceus(PP) and were used to ferment buckwheat dough. Their influence on physicochemical properties, nutritional characteristics and rheofermentation properties were determined. Based on these properties, the preferred strains were selected and used to make buckwheat sourdough bread. Three enzymes: xylanase(XY), transglutaminase(TG) and lipase(LI) were combined with sourdough and their effects on the staling characteristics of bread was investigated.The results reveated that all LABs grew very well in buckwheat dough. In the first 10 hours, the growth and metabolism were fastest and large amounts of lactic acid and acetic acid were produced, resulting in a decrease p H of sourdough to around 4. However, with long fermentation time, the p H of sourdough remained stable and TTA increased.Nutritional characteristics significantly improved with LAB fermentation, with differences noted between different strains. Using HPLC to analyze the content of free amino acids, it was found that after LP fermentation, the content of amino acid significantly increased 70.77% compare to the unfermented dough; the E/T(essential amino acid and total amino acid ratio) of LF fermented dough was 38.31%, higher than others. The total flavonoids content and the antioxidant activity increased during and after the fermentation of sourdough. LP fermented sourdough had the highest antioxidant capacity. During the fermentation process, total flavonoids of LPS was higher than other sourdough and total phenolic content, ABTS and DPPH radical scavenging capacity increased 21.27%, 18.28% and 3.05 times more than the unfermented dough. LAB was able to produce exopolysaccharide which improved the adverse effects caused by acidification. LFS produced the most exopolysaccharide compared to than other sourdough; therefore, the values of Hm, Tx and R of LFD were closer to the unfermented buckwheat dough.A response surface method was used to determine the fermentation time and amount of LP and LF fermented sourdough to be used to make bread. The specific volume and crumb hardness were measured as responses. The optimum fermentation time and amount of LPS and LFS were 9.27 h, 20.99% and 9.41 h, 18.29%; the responses, the specific volume were 4.33 m L/g and 5.07 m L/g and hardness were 471.31 g and 369.25 g, respectively. For further study, the fermentation time and amount of two LABs fermented sourdough was 10 h and 20%.The effect of LP and LF fermented sourdough on baking properties was studied. The results showed that LFS improved the negative effect of adding buckwheat dough, the baking properties of LF fermented buckwheat bread was closer to wheat bread. The content and type of volatile flavor compounds of the two LABs fermented bread were richer than unfermented bread. LABs fermentation significantly improved the antioxidant activity that decreased after baking. Generally, the antioxidant properties of fermented buckwheat bread were higher than the unfermented bread.Addition of the enzymes played an important role in delaying the staling of bread. When the amount of XY, TG and LI was 2 mg/100 g, 0.75 g/100 g and 7.5 mg/100 g, specific volume of bread increased and crumb hardness decreased. LAB fermented sourdough retarded the increase of hardness and retrogradation enthalpy during storage, while the combination of enzymes and sourdough was more effective in improving bread staling.