Selection of autochthonous starter cultures for Malga cheese production

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 aim of this work was to select autochthonous lactic acid bacteria (LAB) strains as dairy starter cultures in order to improve the fermentation process. 243 mesophylic and 164 termophylic LAB were isolated from the raw milk curdle and the cheese after one day. All bacterial isolates were clustered by Randomly Amplified Polymorphic DNA Polymerase Chain Reaction (RAPD-PCR) using two primers and identified by partial sequencing of 16S rRNA gene and species-specific PCR. After clustering by RAPD-PCR we obtained 245 biotypes that were tested for their technological properties (acidifying, proteolytic, autolytic activities and coliforms growth inhibition ability). In order to use them in scaled-up cheese-making process, 20 strains were selected because showing better acidifying and autolytic activities and some ability in coliforms growth inhibition. These 20 strains were also tested for their resistance to freeze-drying process. Lactococcus lactis strains showed the fastest acidifying ability lowering the milk pH to 4.5 in 12 hours both at 30 and 15 °C. Streptococcus thermophilus strains showed the best acidifying ability lowering the milk pH to 3.5 but their acidifying activity needed at least 36 hours. They also showed the highest autolysis values (their values ranged between 30 and 70%). All the strains showing inhibition of coliforms’ growth.belonged to Enterococcus faecium or faecalis species. The 20 strains selected for cheese-making process showed a surviving ability to freeze-drying test between 15 and 20%. The development of autochthonous starter cultures selected on the basis of technological tests would ensure the dominance of desired strains in the first hours of ripening that is crucial to minimize microbial variability and growth of undesired spoilage bacteria which could survive during the further ripening.