Microbial ecology of Malga cheese as spontaneously fermented cheese.

Malga cheese is made from raw cow’s milk without addition of starter cultures, in small scale on-farm plants or huts during the summer season. Huts are located at least 1400 meters above the sea level in Trentino, an alpine province in northern Italy. The objectives of the present study were to characterize lactic acid bacteria (LAB) in the first stage of Malga cheese production and during ripening, and to relate lactic microbiota to cheese technological and physico-chemical parameters including pH, water activity and sensorial attributes. About 30 days of cheese-making were followed and sampled (vat raw milk, the curdle, the cheese at 1 day, one month and 7 months ripening). Different microbial groups were enumerated on selective media (PCA, M17, MRS, VRBA and KEA) under appropriate incubation conditions. 800 strains were isolated and the lactic ones were genotypically characterized combining Randomly Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR), species-specific PCR and partial sequencing of 16S rRNA gene. The milk microflora was heterogeneous and constituted by both mesophylic LAB and not-LAB psycrotrophic species. Untill one month ripening lactic microbiota was mainly constituted by mesophilic cocci-shaped LAB identified as Lactococcus lactis. Enterococcus faecalis and Streptococcus thermophilus were also found at the beginning of ripening but always at lower counts than mesophylic LAB probably because the low cooking temperature (44 °C) was not selective enough for thermophilic populations. Non LAB isolates, mainly belonging to Enterobacteriaceae genus, were found among dominant microbial population but only in the first day of production (mean count ranging between 2.9 and 4.7 log cfu / g). During the cheese ripening, the number of enterobacteria decreased concomitantly with pH. At 7 months of ripening, the cheese microbiota was constituted mainly of Lactobacillus strains. This study has provided an inventory of lactic acid bacterial strains used in the production of traditional Malga cheeses and constitutes a valuable biotechnological resource to prevent and save and a good alternative to introduction of industrial starter cultures.