This study was conducted to investigate the effect of soymilk fermented by Lactobacillus amylolyticus L6 on intestinal microorganisms and short-chain fatty acids in vitro. After simulated gastrointestinal digestion of the fermented soymilk, the survival rate of L. amylolyticus L6 was determined. Then, the digested product was inoculated with human fecal microorganisms and cultured at 37 ℃ under anaerobic conditions for 48 h, and the changes of short chain fatty acids were determined during the fermentation process. The relative abundance of intestinal flora was analyzed by 16S rRNA sequencing. The results showed that L. amylolyticus L6 in the fermented soymilk maintained a high survival rate after simulated gastrointestinal transport. After 48 h in vitro fermentation with the fermented soymilk, the relative abundance of many harmful intestinal bacteria decreased, and the content of short-chain fatty acids (SCFAs) increased significantly (P < 0.05). These findings suggest that L. amylolyticus L6 fermented soymilk can increase the content of SCFAs after 48 h in vitro fermentation. This study provides a theoretical guidance for the development of fermented soybean products.

The high-glucose tolerance of yeast is the main factor determining the efficiency of high-density alcohol fermentation. Zygosaccharomyces mellis LGL-1 isolated from honey could survive under 700 g/L high-glucose stress and its tolerant characteristics were identified in our previous study. This study was performed to explore and clarify the high-glucose tolerance mechanism of Z. mellis LGL-1. Comparative transcriptomic analysis was used to analyze the genes with differential expression in Z. mellis under high-glucose conditions of 300, 500 and 700 g/L. With 300 g/L samples as reference, there were 937 and 2380 differentially expressed genes (DEGs) in the 500 and 700 g/L samples, respectively. Meanwhile, there was 825 significant DEGs in the 700 g/L samples compared with that of the 500 g/L samples. The result revealed that transcriptional changes in multiple metabolic pathways occur in response to high-glucose stress. q-RT PCR analysis further confirmed that several stress response pathways, such as the high osmolarity glycerol mitogen-activated protein kinase (HOG-MAPK) signal transduction pathway, trehalose synthesis pathway and oxidative stress response are closely related to high-glucose tolerance in Z. mellis. This study clarifies mechanisms of Z. mellis in response to high-glucose osmotic stress, providing theoretical basis for the process control of high-density alcohol fermentation.