Proteomic Profiling and Cytotoxic Effects of Short-Chain Protein Hydrolysates from Bacillus siamensis MH3-Fermented Soybean Meal on Colon Cancer Cells

Soybean meal fermented via solid-state fermentation produces protein hydrolysates enriched with short-chain peptides, which exhibit enhanced biological activities compared with larger peptides. This study aimed to analyze their protein composition, antioxidant activity, cytotoxicity against colon cancer cell lines, and proteomic analysis. The soybean meal fermented with Bacillus siamensis serotype MH3 for 72 h (MH3-72), digested with pepsin, and extracted with a 3 kDa molecular weight cutoff, contained approximately three times more protein content than unfermented soybean meal (SB) and prefermentation samples (MH3-0). Antioxidant activity, measured using DPPH and FRAP assays, was retained in MH3-72. MTT assays revealed that MH3-72 was significantly cytotoxic to colon cancer cells (SW480) but nontoxic to normal cells (Vero). Peptide sequence analysis indicated that most peptides originated from glycinin and beta-conglycinin, ranging from 1000 to 2900 Da. Proteomic analysis identified 11 upregulated proteins and 25 downregulated proteins associated with metabolic pathways. These findings improve our understanding of soybean meal proteomics after B. siamensis serotype MH3 fermentation and highlight its potential for inhibiting colon cancer cell growth while providing antioxidant properties.