Effect Of Casein Hydrolysates On Fermentation And Bacterial Construction In Buckwheat Sourdough

Buckwheat is an ideal healthy cereal food with comprehensive nutrients and various physiological functions.In recent years,the application of buckwheat in baking products is increasing.However,due to the gluten-free structure of buckwheat sourdough and the poor quality of the finished product,consumers'acceptance of buckwheat products is low.Therefore,improving the quality of buckwheat cereal products and increasing consumer acceptance are important issues that need to be resolved urgently.Studies have shown that protein hydrolysates can promote the growth and proliferation of lactic acid bacteria and improve the network structure of dough.In this study,casein hydrolysates was selected as an additional nitrogen source for lactic acid bacteria(LAB)in buckwheat sourdough,and its effects on the fermentation characteristics and bacterial construction of buckwheat sourdough were investigated.In this study,the fermentation characteristics of buckwheat sourdough were anal yzed by measuring the pH value,TTA value,LAB count,and fermentation ability of sourdough during fermentation of buckwheat sourdough;the metabolic ability of LAB in buckwheat sourdough was analyzed by measuring the content of two kinds of organic acids in the fermentation process;the degradation of protein and sugar in buckwheat sourdough was investigated by analyzing the changes of protease activity,reducing sugar content and protein content in sourdough;the quality of buckwheat sourdough was investigated by analyzing the texture and microstructure of the sourdough;the bacterial construction of natural fermented buckwheat sourdough was analyzed by high-throughput sequencing,and its correlation with environmental factors was analyzed.The results show that:Adding casein hydrolysates could increase the acidity of naturally fermented buckwheat sourdough system by 6.4%,and reached the established acidity at least 4 hours in advance,which greatly shorten the fermentation time.The LAB count in yeast fermented sourdough was far lower than that in natural fermentation.After 9 hours of fermentation,the LAB count in naturally fermented buckwheat sourdough reached 10~9CFU/g.The addition of casein hydrolysates in naturally fermented sourdough is beneficial to the growth of LAB in buckwheat sourdough.The addition of casein hydrolysates can significantly increase the fermentation ability of naturally fermented sourdough,but it has an adverse effect on the fermentation ability of yeast fermented sourdough.After adding casein hydrolysate,the organic acid content of naturally fermented buckwheat sourdough was significantly higher than that without casein hydrolysates(p<0.05),and the content of lactic acid and acetic acid increased by 58.28%and 23.39%,respectively.Adding casein hydrolysate was conducive to the metabolism of LAB in naturally fermented buckwheat sourdough.Compared with unfermented sourdough,the protease activity of buckwheat sourdough was significantly improved(p<0.05)after fermentation.The addition of casein hydrolysates was beneficial to increase the protease activity of natural fermented buckwheat sourdough,which was33.78%higher than that without casein hydrolysates.The protein degradation of naturally fermented buckwheat sourdough was obvious,while the protein degradation in yeast fermented buckwheat sourdough was negatively affected.The addition of casein hydrolysates promoted the utilization of reducing sugar by LAB and other microorganisms in buckwheat sourdough,and the addition of yeast also increased the consumption of reducing sugar in the system.The hardness of buckwheat sourdough decreased significantly(p<0.05),and the adhesiveness increased significantly(p<0.05)after fermentation.The naturally fermented sourdough added with casein hydrolysates has the best springiness,cohesiveness and resilience.The addition of casein hydrolysates was more conducive to the formation of spatial network structure of buckwheat sourdough and had positive effect on the improvement of the texture of buckwheat sourdough.The bacteria construction of naturally fermented sourdough changed after adding casein hydrolysates.Lactobacillus was the dominant genera,and Pediococcus was the secondary dominant genera.Meanwhile,the relative abundance of Weissella increased significantly(p<0.05),and that of Enterobacter and Enterococcus decreased significantly(p<0.05).The environmental factors such as pH value,TTA value and organic acid content were correlated with the bacteria construction of naturally fermented buckwheat sourdough.In a word,the addition of casein hydrolysates can increase the proportion of LAB in naturally fermented buckwheat sourdough,enhance the metabolic activity of LAB,shorten the fermentation time,improve the acidity and fermentability of the sourdough system,and improve the texture and microstructure of the sourdough.It has a positive effect on the improvement of the quality of naturally fermented buckwheat sourdough.