Microbial diversity, dynamics and activity throughout manufacturing and ripening of Castelmagno PDO cheese

Abstract

The diversity, dynamics and activity of Castelmagno PDO cheese microbiota were studied in three batches produced in a floor valley farm, in the Grana Valley (northwest Italy), during the wintertime. Samples of milk, curd and cheese (core and subsurface) at different ripening time were submitted to both culture-dependent and -independent analysis. In particular, DNA and RNA directly extracted from the matrices were studied by PCR-Denaturing gradient gel electrophoresis (DGGE) and reverse transcription (RT)-PCR-DGGE. Culture-dependent methods highlighted the initial dominance of a thermophilic streptococcal population with the species Streptococcus thermophilus and S. agalactiae. Then, mesophilic lactococci occurred among isolates during manufacturing, with Lactococcus lactis which was also well represented in the first month of Castelmagno PDO ripening. At this point and throughout the ripening, lactobacilli prevailed in cheese samples, represented from Lactobacillus plantarum and Lb. casei. Culture-independent analysis underlined the undoubted role of L. lactis, actively involved in both Castelmagno PDO manufacturing and ripening. Despite Lb. helveticus was never isolated on selective media, a DGGE band referred to this microorganism was detected, at RNA level, in samples from ripened cheeses. On the other hand, Lb. plantarum was widely isolated from the plates, among lactobacilli, but never detected by direct analysis. Due to the importance of microbiota in the sensory richness and properties of traditional cheeses, new information have been added, in this work, on microbial diversity of Castelmagno PDO cheese.