Application of sesame peptides in soymilk: Impact of food matrix effects on antibacterial activity of natural plant-based preservatives

This study evaluated the antibacterial efficacy of sesame protein hydrolysate with a molecular weight cut-off below 10 kDa (<10SPH) against Escherichia coli and Bacillus cereus, focusing on the impact of food matrix effects (pH, sucrose, and sodium chloride (NaCl)) on their antimicrobial activities. This peptide exhibited much stronger antimicrobial activity against B. cereus (gram-positive) than E. coli (gram-negative), which was mainly attributed to differences in bacterial membrane structure and composition. The thermal resistance of both pathogens was assessed in soymilk with and without <10SPH by determining the D-values at 50, 55, and 60 °C. The antimicrobial activity of the peptides was found to be dependent on the surrounding food matrix, including pH, sucrose, and NaCl conditions. In particular, acidic conditions (pH 4) reduced the activity of the antimicrobial peptides against E. coli, whereas high salt concentrations (1–5 %) increased their activity. Thermal inactivation results showed that both E. coli and B. cereus in soymilk were slightly less resistant to heat after <10SPH was added. The calculated z-values were 7.01, 7.09, 7.04, and 7.56 °C for E. coli in soymilk, E. coli in <10SPH soy milk, B. cereus in soymilk, and B. cereus in <10SPH soymilk, respectively. The inclusion of <10SPH in soymilk therefore enhanced microbial inactivation, demonstrating its potential as a natural plant-based preservative. These findings provide valuable insights into the impact of food matrix effects on the antimicrobial activity of plant-derived peptides, which may be useful for optimizing their performance in plant-based food products.