Comparative analysis of proteolytic activity in lactic and propionic acid bacteria: substrate specificity and complementary effects in dairy fermentation

Abstract

This study presents novel insights into the proteolytic activity of lactic acid bacteria (LAB) and their combinations with propionic acid bacteria (PAB), addressing the current gap in understanding the mechanisms of milk protein hydrolysis during dairy fermentation. The research involved a comprehensive analysis of 12 strains of Lactococcus spp. and 4 strains of Streptococcus spp., along with their combinations with PAB. Using SDS-PAGE electrophoresis, spectrophotometry, and high-performance liquid chromatography, the study investigated the proteolytic characteristics of these microorganisms during skim milk fermentation. Key findings revealed distinct patterns of protein hydrolysis. Preferential cleavage of β-casein was shown for the L. lactis 782 M-A proteolytic system, whereas S. thermophilus 1095 ST-AV, Propionibacterium sp. 2388 MYO-К and L. casei 1188 ML-OF hydrolysed α- and β-casein. However, whey proteins were not found to be proteolysed. Notably, the combination of PAB with lactococci demonstrated enhanced casein hydrolysis compared to individual strains. The research identified varying levels of proteolytic activity among different strains. The maximum proteolytic activity recorded was 2.54–3.12 mg/ml for Propionibacterium sp. 2388 MYO-K. The most significant finding was the complete hydrolysis of the casein fraction observed when milk was fermented by PAB in combination with lactococci or the L. lactis 782 M-A and S. thermophilus 1095 ST-AV combination. The results obtained can be applied to optimize fermentation processes and develop functional dairy products with tailored protein-peptide profiles. The results contribute to a better understanding of how to select appropriate bacterial strains for specific dairy fermentation processes based on their proteolytic characteristics.