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 composition of the natural whey starter and its modification in response to curd cooking were considered. The growth and distribution of the thermophilic lactobacilli in the cheese at 48 h after molding was affected by the temperature gradient between the external and internal cheese zones. Growth was maximum between 0 and 6 h in the cheese exterior and between 6 and 24 h in the core. This variation occurred because the cheese interior was around 52°C 6 h after molding, which is far from the optimum for the thermophilic lactobacilli growth. Dot-blot hybridization 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 delbrueckii and the heterofermentative lactobacilli, which slowly increased from the molding until 48 h, was more variable in the internal regions than in the external regions of the cheese. This study demonstrates that the thermophilic lactobacilli behave differently during the technological process than during experiments using laboratory models.