Microbial diversity in Natural Whey Cultures used for the production of Caciocavallo Silano PDO cheese

Abstract

The microbial diversity of sixty-three Natural Whey Cultures (NWCs) for the manufacture of Caciocavallo Silano cheese PDO was studied. The NWCs were collected from different dairies covering the whole territory of PDO production including five different regions of southern Italy. The microbial species diversity was determined by direct DNA extraction from NWCs and Polymerase Chain Reaction (PCR) amplification of variable regions of the 16S rRNA gene followed by denaturing gradient gel electrophoresis (DGGE) and denaturing high performance liquid chromatography (DHPLC). DGGE and DHPLC fingerprinting yielded the same results in terms of number of bands/peaks and specific migration/retention time of the amplicons. The DHPLC technique was used in this study for the first time to assess a food-related mixed microbial community by a culture-independent approach and proved to be at least as effective as DGGE in profiling species diversity in NWCs. Cluster analysis of DGGE and DHPLC data revealed that the species-related groups of similarity were not dependent on the geographical origin of the NWCs. The presence of three groups of 10–14 NWCs at 100% of species similarity indicated that some species associations are very commonly occurring in the NWCs for Caciocavallo Silano cheese PDO. A RAPD-PCR analysis of the NWCs was also performed for the members of the above groups and it showed that, though characterized by the same species diversity, most of the identical NWCs included different biotypes. The sequences of DGGE bands and DHPLC peaks revealed the occurrence of mainly thermophilic lactic acid bacteria such as Lactobacillus delbrueckii, L. helveticus and Streptococcus thermophilus even though the mesophilic Lactococcus lactis also occurred in some NWCs. In conclusion, the results of this study indicate that the microbial diversity of NWCs used for the Caciocavallo Silano PDO cheese is not high, it is not dependent on the geographical origin and the same microbial species occur within the territory examined. The microbiota of fermented PDO products and its possible link with territory should be studied case by case in order to have useful evidences for the assessment of product quality and authenticity.