AUTOLYSIS OF LACTOBACILLUS-HELVETICUS AND PROPIONIBACTERIUM-FREUDENREICHII IN SWISS CHEESES - FIRST EVIDENCE BY USING SPECIES-SPECIFIC LYSIS MARKERS

Lactobacillus helveticus and Propionibacterium freudenreichii are esse ntial starters in Sn iss cheesemaking and the release of their intrace llular enzymes through autolysis could significantly influence ripenin g. To provide evidence of this lysis: cheese made from microfiltered t hermized milli inoculated with Lb. helveticus ITGLH77, Prop. freudenre ichii ITGP23 and a commercial Streptococcus thermophilus was assayed. Starter viability was determined and lysis was monitored during ripeni ng by protein analysis with SDS-PAGE of aqueous cheese extracts and by immunoblot detection of intracellular proteins: dipeptidase (PepD) fo r Lb. helveticus and methylmalonyl coenzyme A mutase for Prop. freuden reichii. We verified that. the species specificity of these lysis mark ers was towards the cytoplasms of all the species currently used in Sw iss cheese. Lb. helveticus exhibited an almost complete loss of viabil ity (99.9%) from the beginning of ripening in the cold room: concomita ntly PepD appeared in the cheese extracts and was detected until the e nd of ripening. Damaged Lk. helveticus cells were also visualized by s canning electron microscopy. In addition, free PepD was also successfu lly detected in commercial Swiss-related cheeses. All these results cl early demonstrated the autolysis of Lb. helveticus in Swiss cheese. Pl op. freudenreichii ITGP23 grew during warm room ripening and no loss o f viability was detected after maximal growth (10(9) cfu/g cheese). Fr ee methylmalonyl-coenzyme A mutase was detected at the end of ripening during cold storage, when the cheese extracts were concentrated 20-fo ld, demonstrating that the autolysis of Prop. freudenreichii was tardy and limited.