Non-starter Lactic Acid Bacteria characterization for their control in cheese making

Cheese making date his practice over millennia and evolved nowadays being part of a sector representing one of the biggest business of the food industry. In the wide cheese variety, raw milk cheeses have particular economic relevance for many European countries. These products owe their popularity to a typic organoleptic profile whose formation is recognized to be strongly influenced by the raw milk microbiota. Non-starter lactic bacteria (NSLAB) represent the part of this microbiota which has shown the capability to better adapt in the cheese environment and their activity has been positively correlated with cheese flavor formation. Although much is known about the cheese microbiota and from which NSLAB species it is composed, further research has been highlighted as necessary to better understand the origin, development dynamics along the production chain, and metabolic traits at the strain level of NSLAB. The object of the present thesis was to do a step forward over what is known about the NSLAB, studying their diversity at the strain level through the characterization of their genotypic, phenotypic and metabolic traits. The knowledge of this information is at fundamental for the control of the interested NSLAB within the complex raw milk microbiota and as consequence govern their effect on the cheese's final characteristics. More than 120 NSLAB strains have been isolated from 20 dairies and screened in order to be qualified as potentially applicable as adjunct cultures. The possibility of positively influencing the cheese characteristic controlling the raw milk microbiota was also investigated by developing a natural adjunct milk culture. Finally, an investigation on hard cheeses produced from centrifugated raw milk gave new insight into the description and consequent prevention of structural defects possibly correlated with the NSLAB abundance unbalancing within the cheese microbiota. The results achieved lay the foundation to a better exploit of the raw milk microbiota, contributing to the possibility of predicting more precisely the final cheese characteristics. Cheese making trials will be necessary to test the effectiveness of the adjunct strains screened in influencing the cheese aroma. In order to obtain the same goal in the context of an artisanal dairy, more research is needed to optimize the natural adjunct milk culture developed, testing different treatments that could more specifically select desired NSLAB present in raw milk.