INFLUENCE OF THE TEMPERATURE-GRADIENT ON THE GROWTH OF THERMOPHILIC LACTOBACILLI USED AS NATURAL STARTERS IN GRANA CHEESE

This study investigated the evolution of the Lactobacillus species and the microbial composition of the starter during Grana cheese making. The early stages of cheese making were studied, and both the compositi on of the natural whey starter and its modification in response to cur d cooking were considered. The growth and distribution of the thermoph ilic lactobacilli in the cheese at 48 h after molding was affected by the temperature gradient between the external and internal cheese zone s. Growth was maximum between 0 and 6 h in the cheese exterior and bet ween 6 and 24 h in the core. This variation occurred because the chees e interior was around 52 degrees C 6 h after molding, which is far fro m the optimum for the thermophilic lactobacilli growth. Dot-blot hybri dization experiments allowed the identification of up to 280 isolates. Lactobacillus helveticus predominated in the natural whey starter and in the external cheese zones. Distribution of Lactobacillus delbrueck ii and the heterofermentative lactobacilli, which slowly increased fro m the molding until 48 h, was more variable in the internal regions th an in the external regions of the cheese. This study demonstrates that the thermophilic lactobacilli behave differently during the technolog ical process than during experiments using laboratory models.