Proteolytic activity of probiotic strain Lactobacillus helveticus M92.

The aim of this research was to investigate the potential of previously defined probiotic strain Lactobacillus helveticus M92 as functional starter culture for fermented dairy products. Therefore, proteolytic activity of L. helveticus M92 was investigated and compared with those of different representatives of probiotic and starter culture strains. Cluster analysis of AFLP fingerprints showed a difference of L. helveticus M92 compared to five other L. helveticus strains, but the percentage of similarity confirmed the identification on species level. Casein hydrolysis by L. helveticus M92 was monitored by agar-well diffusion test, SDS-PAGE and Anson's method. L. helveticus M92 exhibited the highest proteolytic activity among tested probiotic and starter cultures strains with the fastest acidification rate and the highest pH decrease after overnight incubation in skim milk. The presence of prtH2 gene was confirmed by PCR amplification with specific primers, while PCR product was not obtained after amplification with primers specific to prtH. Furthermore, SDS-PAGE LC-MS/MS analysis of insoluble proteome of L. helveticus M92 enabled identification of several proteins involved in proteolytic system of L. helveticus such as protease PrtM as well as proteins involved in Opp peptide transport system and the intracellular peptidases PepE, PepN, and PepQ.