Fermentation Characteristics of Tartary Buckwheat Sourdough by Exogenous Lactic Acid Bacteria and Quality Change of Frozen Dough Bread

In this study, Lactobacillus plantarum (Lp), Lactobacillus fermentum (Lf) and Weissella confusa (Wc) were selected as exogenous strains for the fermentation of sourdough. The growth of lactic acid bacteria, the distribution of major metabolites such as organic acid and sugar, and the distribution of protein in sourdough were evaluated by high performance liquid chromatography (HPLC) and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Finally, the sourdough was applied to the production of frozen dough bread. The results showed that in the sourdough, the bacteria entered the logarithmic growth phase at 4–12 h, and mixed cultures grew better than individual ones, showing synergism. Particularly, the colony count of Lf + Wc in sourdough was as high as 9.18 (lg(CFU/g)) after 12 h fermentation, and a large amount of fructose (11.82 mmol/kg) and extracellular polysaccharide (EPS) (3.132 g/kg) were generated. Compared with the other groups, Lf + Wc exhibited moderate acid production rate, lower protease activity and slower protein degradation rate. The baking quality of bread made from Lf + Wc fermented sourdough frozen and stored for 13 weeks decreased slightly, and the baking loss rate decreased only by 5.3%. In addition, GC-MS analysis showed that the number of volatile compounds in frozen dough bread fermented with Lf + Wc increased by eight after 13 weeks of frozen storage. In conclusion, Lf and Wc have a good synergistic effect when used together. Notably, metabolites such as exopolysaccharides generated during metabolism are of great significance for delaying and controlling the deterioration of frozen dough bread quality. This study provides a certain theoretical basis for the application of multigrain sourdough as a natural antifreeze agent in the large-scale preparation of frozen dough.