Fructilactobacillus sanfranciscensis, the dominant species of lactic acid bacteria in sourdoughs, impacts the microstructure and flavor of steamed bread through exopolysaccharide production, acidification, proteolysis, and volatile compound generation. The aim of this study is to investigate the phenotypic diversity and technological traits of 28 F. sanfranciscensis strains of different genotypes isolated from Chinese traditional sourdoughs. The results showed that F. sanfranciscensis strains exhibited substantial variation in proteinase and peptidase activities and the amount of acidification and volatiles in fermented sourdoughs. However, we observed no significant differences in exopolysaccharide production among the strains. The strains Sx14 and Ts1 were further chosen for transcriptomics to gain a deep insight into their intraspecies diversity in sourdough fermentation. Significant transcriptome differentiations between these two strains after 12 h fermentation in sourdoughs were revealed. According to the results, the strain Sx14 possessed higher dipeptidase and aminopeptidase activities, galactose utilization, and lactic and acetic acid production abilities, whereas Ts1 showed higher transmembrane transport of substrates and fructose utilization.

The influence of lactic acid bacteria (LAB) strains of various species isolated from Chinese traditional sourdough on the properties of rice sourdough and the textural and flavor qualities of steamed rice bread (SRB) was investigated. Lactiplantibacillus plantarum-fermented rice sourdough had a higher total titratable acidity (13.10 mL) than the other groups. Strains Lacticaseibacillus paracasei PC1 (LPC), Lactobacillus helveticus H1 (LH), Lactobacillus crustorum C1 (LC), Lactobacillus paralimentarius PA1 (LPA), and Lactiplantibacillus plantarum P1 (LP) showed marked protein hydrolysis during rice sourdough fermentation and increased free amino acid levels in rice sourdoughs relative to the control. The Fourier Transform Infrared Spectroscopy results indicated that LAB fermentation could promote the strengthening of inter-intramolecular hydrogen bonds and cause modifications in protein structures; however, these effects varied among the different strains. The LC and LPC strains had the most significant effect on improving the specific volume and textural properties of SRBs. Gas chromatography-mass spectrometry (GC-MS) and GC-ion mobility spectrometry (IMS) identified 33 and 35 volatile compounds, respectively, in the LAB-fermented SRBs, and differentiation was observed in the volatile profiles of SRBs made using different LAB strains. The differential impacts of LAB strains during rice sourdough fermentation can assist in the selection of candidate microorganisms for the production of high-quality gluten-free rice products.