Search

Bacillus spp. are the dominant spoilage organisms in a rehydrated non-fermented soy product, Sichuan yuba in China. In this study, we used two spoilage Bacillus amyloliquefaciens strains DY1a and DY1b to evaluate their destructive capability on rehydrated Sichuan yuba at 25 °C. Compared with the uninoculated soy product, the texture profile of the inoculated samples showed that the hardness, springiness, chewiness, and cohesiveness decreased significantly. Scanning electron microscope (SEM) revealed that the surface of bacteria-inoculated soy product was scattered with deep holes and loose film network structure. The subsequent analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that the α and α' subunit of 7S globulin and the acid subunit of 11S glycinin were hydrolyzed by Bacillus during storage. In addition, disulfide bond contents in inoculated samples decreased by 38.7–27.5%. Protein secondary structure characterized using Fourier transform infrared spectroscopy (FTIR) revealed that spoilage Bacillus inoculation reduced the β-sheet by 13.02–14.11%, and increased the β-turn by 15.55–16.00%. Consequently, the texture deterioration of Sichuan yuba was associated with soy protein degradation caused by B. amyloliquefaciens. • Textures and protein changes of rehydrated Sichuan yuba inoculated with spoilage Bacillus were analyzed. • B. amyloliquefaciens could hydrolyze the α and α′ subunit of 7S and the acidic subunit of 11S. • B. amyloliquefaciens changed molecular interactions and the secondary structure of soy protein. • Protein degradation by B. amyloliquefaciens contributed to the texture deterioration of rehydrated Sichuan yuba. [ABSTRACT FROM AUTHOR]