Milk microbiota investigation during and after summer Alpine transhumance and relation with cheese

Temporary summer alpine farms, called ‘Malga’ in Italy, contribute to the maintenance of the environment, landscape, local traditions and typical dairy production. Malga cheese is made with raw cow’s milk and is characterized by a peculiar flavour. Our aim was to investigate milk microbiota in summer pasture and in autumn, after the transhumance, in lowland during indoor farming and to characterize milk composition, cheese-making properties and quality. The project involved 4 permanent farms (PF) moving the cows on 4 summer farms located at Passo Vezzena (Trentino). Milk samples were collected in mid-July in Malga, from 26 Italian Simmental cows (5-7 per farm), and in mid-October, during lowland indoor feeding based on hay and compound feed. Each milk sample was investigated for the total aerobic and anaerobic bacteria, for the technological potential (lactic acid bacteria, LAB), presence of putative healthy bacteria (bifidobacteria, propionibacteria) and pathogenic bacteria (coliforms, haemolytic streptococci, prototheca). Over 200 bacterial isolates from MRS, MRS-cys, YELA, and WC plates were considered for the identification by 16S rDNA gene sequencing. Individual milk samples were also analysed for microbiota composition by Miseq Illumina, milk composition, milk coagulation properties, nutrient recovery in curd, cheese yield and composition. The data were analysed with a mixed model including the fixed effects of farm, period and their interaction, and the random effects of individual cows and residual. The results revealed high variability among milk plate counts. Coliform, LAB, total bacterial counts, propionibacteria, bifidobacteria, β-haemolytic streptococci were significantly lower in Malga compared to PF, by contrast α-haemolytic streptococci counts were higher. The metagenomics analysis confirmed the high variability of the microbiota in milk produced during and after summer highland pasture. Moreover, we confirmed that the milk microbiota has implications for the change in the cheese-making attitude of milk and the quality of cheese obtained.