Microbiota characterization and volatile and non-volatile lipophilic fraction analysis of Bitto Storico cheese produced in six different Alpine pastures.

The Bitto Storico is an alpine heritage cheese made with raw milk and produced during the summer season in the Orobic Alps (Central Alps, Northern Italy). The cheese-making process depends on local traditions: freshly milked cow's milk is added to fresh goat's milk (10-20%), then production starts immediately in the "calècc" (itinerant dairy). The use of feeds and silage for animal feeding and the use of probiotics during curdling are prohibited thus the organoleptic variability of the cheese depends on local bacteria that change according to pastures and environment. These conditions guarantee a variability of organoleptic characteristics, probably associated to different microbial communities, highly appreciated by consumers. The objectives were (i) the characterization of the microbial variability of the Bitto Storico cheese by Next Generation Sequencing, and (ii) the analysis of the volatile and non-volatile lipophilic fractions. Samples were collected from 54 Bitto Storico cheeses produced in six different Alpine pastures, in three geographical areas (Val Gerola, Valli del Bitto, Valle Brembana), during 2015 summer season. Bacterial DNA was extracted using an optimized protocol and 16S rRNA gene amplicons on V3-V4 region analyzed by Miseq (Illumina). The lipophilic fraction was characterized by means of Solid Phase Extraction-Gas Chromatography-Mass Spectrometry (SPME-GC-MS), the fatty acid profile by the High Resolution Gas Chromatography (HRGC). Preliminary results showed a microbial community mainly dominated by Firmicutes with a high abundance of Streptococcaceae and Lactobacillaceae and low presence of Entrococcaceae. The volatile metabolome displayed a variability consistent with the dairy products of raw milk.