Biochemical Characteristics of Tannase-Producing LAB Fermented Red Beans and Lentils Sourdough and Its Effects on in Vitro Digestibility of Steamed Bread

In this study,a strain of Lactobacillus fermentum D23 with high yield of tannase,which was selected from the naturally fermented legume flour in the previous research of this group,was used to make red beans and lentils sourdough and steamed bread. By determining the content of anti-nutritional factors such as condensed tannin,peptide molecular weight distribution,content of free total phenols and free amino acids before and after sourdough fermentation,and the in vitro digestibility of starch and protein in steamed bread,the biochemical characteristics of sourdough and in vitro digestibility of steamed bread were studied to make a comparative research. The results showed that through the fermentation of D23,the content of condensed tannin in these two kinds of legume sourdough decreased significantly(P<0.05),by 57.87% and 53.54% in red beans and lentils sourdough,respectively. The content of large molecular weight peptides decreased,and the content of small molecular peptides increased.The content of free total phenols increased by 75.74% and 65.94%,respectively. The essential amino acid content increased by 429.31% and 358.20%,respectively. The content of reducing sugar in the final digestive juice of sourdough steamed bread increased by 3.27% and 5.55%,respectively.Compared with the unfermented group,the in vitro digestibility of starch was improved,and the final in vitro digestibility of protein also increased from 67.68%,70.21% to 73.21%,76.97% respectively. Therefore,the strain D23 with high tannase activity can effectively reduce the adverse effects of anti-nutritional factors such as condensed tannins in legume matrix,and enhance the nutritional value of final steamed bread products through the process of sourdough fermentation,which gives the strain a good application potential in fermented legume products.