Analysis of okara soybean by-product peptides with antimicrobial properties

Abstract

One-quarter of total food production is lost globally due to food spoilage and contamination. Furthermore, synthetic food preservatives have increased their use in the food industry to address this issue even though they have been related to potential health risks. In this study, okara, a by-product waste from the soymilk production process was evaluated as a source of bioactive peptides which could act as a natural alternative to synthetic food preservatives. An experimental design of two kinds of okara were generated to compare the peptide profile through the time. One in which protein extraction happened immediately after okara generation, and another in which microbial growth was allowed for a week before protein extraction. Protein quantification assay and SDS-PAGE analysis were used to evaluate the protein composition changes. Antimicrobial analysis using disk diffusion susceptibility test against common foodborne pathogens was used. The protein quantification assay indicated a ten-fold decrease in protein content for the batch with microbial growth. SDS-PAGE analysis showed the presence of low molecular weight peptides when microbial growth occurs in okara, which is attributed to the proteolytic activity on enzymes during okara fermentation. Furthermore, antimicrobial analysis demonstrated that protein extract from okara with microbial growth has more antimicrobial effects against Staphylococcus aureus compared to food preservative sodium benzoate. In this regard, okara promises to be a valuable source of bioactive peptides when endogenous microorganisms are allowed to grow, but further studies and methods are needed to characterize okara derived peptides.