Changes in the Bacterial Phases of Soybean Curd Sheets and Analysis of Spoilage Ability of Dominant Bacteria Stored at Normal Temperature

The bacterial phase changes and the effect of dominant spoilage bacteria on quality were studied with traditional identification method and high-throughput sequence technique using Chinese traditional food soybean curd sheets as materials. Sterile soybean curd sheets were inoculated with three dominant bacteria and their combination. The total viable counts, total volatile base nitrogen (TVB-N), pH, sensory score, and texture characteristics of samples during normal temperature storage were measured periodically for spoilage potential. The scanning electron microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and Fourier transform infrared spectroscopy (FTIR) were used to determine the effect of spoilage bacteria on the protein. The results indicated the bacterial phases of soybean curd sheets changed obviously during storage, and Acinetobacter, Staphylococcus as well as Kurthia became the dominant bacteria after 2 days of storage. The selected representative spoilage bacteria were re-inoculated to the samples, one protease-producing Staphylococcus sciuri and the mixed bacteria had the strongest spoilage potential, because the TVB-N and viscosity increased greatly, while the hardness, springiness, and chewiness decreased significantly (P