The spatial distribution of bacteria in Grana-cheese during ripening

The microbial composition and spatial distribution of Grana Trentino, a hard Parmesan-like cheese, was evaluated, from vat milk to cheese. After cutting along the vertical axis of the cheese wheels, three layers were sampled diagonally across the cheese: under the cheese rind, an intermediate section and the cheese core. After two different ripening periods (9 and 18 months), the cheese samples were analyzed using traditional culture dependent and culture independent methods. Milk samples were dominated by mesophilic and psychrotrophic bacterial counts. Thermophilic bacteria (Lactobacillus helveticus) where found in high amounts in cooked whey and natural whey starter cultures. After 9 months of ripening, lactic acid bacteria (LAB) counts were higher than those after 18 months. Furthermore, the LAB numbers in the cheese core was lower than those under the rind or in the intermediate section. The main LAB species isolated from milk (Lactococcus lactis, Pediococcus pentosaceus, Streptococcus uberis and Lactococcus garvieae,) were not found in the corresponding cheeses. Some differences were observed in species composition among the three cheese sections. Microbiota under the rind and in the intermediate section was similar and dominated by Lactobacillus paracasei and Lactobacillus rhamnosus. The core, after 18 months of ripening, was characterized by a total absence of LAB. In each sample, all LAB were genotypically grouped and the different biotypes were subjected to several technological tests finding out that some non-starter LAB (NSLAB) were characterized by technological properties suitable for Grana Trentino cheese production.