Factors affecting viability of selected probiotics during cheese-making of pasta filata dairy products obtained by direct-to-vat inoculation system

Aim of the study was to produce probiotic "mozzarella" and "scamorza", two traditional Italian pasta filata cheeses, by direct-to-vat inoculum of probiotic adjuncts, the main method deliver system used by dairy factories to produce fermented cheeses. Factors that affect the adjuncts viability during cheese-making were evaluated and the identity of the surviving probiotics was ascertained by 16SrDNA sequencing. Five commercial probiotic cultures were selected for acidifying, growth ability and capability to tolerate high temperatures. The best selected probiotic, together with primary starter, was used for production in large scale of "mozzarella" and "scamorza" following procedures of the dairy farm. Results highlighted that stretching curd step is detrimental for probiotic viability reducing more than 2 log cfu/g probiotic load. In our experimental conditions, "mozzarella" could not be considered a good carrier of probiotic because the shelf-life at refrigeration temperature did not allow to re-establish a reasonable dose of probiotics. On the contrary, a ripening of at least 30 days at 15 °C could assure an increase in probiotic load from 10- to 100-fold, prove that semi-ripened cheese, as "scamorza", obtained by direct-to-vat inoculum system, can be a food-based vehicle for probiotics. Furthermore, sensory analysis showed that probiotic-enriched and traditional "scamorza" were comparable.