Caseinolytic proteases of Lactobacillus and Lactococcus strains isolated from fermented dairy products

Abstract

Proteases of Lactobacillus and Lactococcus strains catalyze casein degradation in fermented dairy products, which can result in the production of bioactive peptides. Proteolytic properties of a selection of lactic acid bacteria (LAB) strains previously isolated in Croatia, including Lactococcus lactis and Lactobacillus strains, are described. All strains of Lactobacillus and Lactococcus showed an Fmc+ phenotype that can be associated with efficient growth in milk. The significant caseinolytic effect, after incubation of culture supernatant or concentrated cell biomass, was observed for Levilactobacillus brevis D6 and Lactiplantilactobacillus plantarum D13 after growth in the optimal growth medium, while for Lc. lactis ZGBP5-32 and Levilactobacillus brevis SF9B strains after growth in skimmed milk. To assess the LAB growth in skimmed milk, the acidification rate was monitored. Statistically, significant acidification capacity was determined for L. plantarum D13 in the optimal medium and by the proteolytic strain L. helveticus M92 in skimmed milk. After extraction of proteinases from the strains with caseinolytic activity, protein samples were analysed by the SDS-PAGE method. The protein extract of the strains Lc. lactis ZGBP5-32 and ZGZA7-10, retained proteolytic activity even at very low concentrations. The ultrafiltration improved protein extraction which possibly contained putative protease, as a decrease in contaminating proteins was confirmed by SDS-PAGE in samples of L. brevis D6 and SF9B, L. fermentum D12 and L. plantarum D13.