Antibacterial activity of protein hydrolysates obtained from enzymatic digestion of soy protein isolate on some food indicator bacteria

In this study, soy protein isolate (SPI) was hydrolyzed using Alcalase with the aim of generating natural antibacterial components. Then, antibacterial activities of resulting protein hydrolysates were investigated against some indicator bacteria including Escherichia coli, Bacillus cereus, and Staphylococcus aureus. Enzyme to substrate ratio (E/S) and hydrolysis time were chosen as process variables. Degree of hydrolysis (DH) and its effects on hydrolysates activity were also evaluated. The maximum DH was observed after protein hydolysis for 90 min at E/S value of 1.5%, which was not significantly different from that observed after 60 min at E/S of 2.5%. According to the results, enzymatic hydrolysis effectively enhanced antibacterial activity of SPI. The obtained hydrolysates showed the highest activity against E. coli and the least effect on B. cereus. Applying higher enzyme concentration showed significant effect on hydrolysis progress and also on inhibitory activity of hydrolysates against E. coli, but not against B. cereus and S. aureus. The effect of increase in hydrolysis time on the inhibitory activity of resulting hydrolysates against different tested bacteria was highly varied. In overall, the results of this study showed that with controlled enzymatic hydrolysis of SPI, peptides with considerable antimicrobial activity against E. coli may be obtained that can be used in food formulation.