Traditional and innovative approaches to evaluate microbial contribution in long ripened fermented foods: the case of Parmigiano Reggiano cheese

Future development and economic growth of dairy industry largely depends on microbial starter used to produce the great majority of industrial fermented products. Moreover, natural cultures implied in traditional cheeses manufacturing, are responsible for many good recognizable traits which make them appreciable all over the word. Even if, great progress has been made toward understanding lactic acid bacteria physiology, and processes that drive quality fermented food development, much remains to be learned. For this reason, a Protected Designation of Origin, appreciated and economically important Italian cheese like Parmigiano Reggiano, has been chosen as subject for this study, to try a better understanding of how and when lactic acid bacteria are involved in these processes. To reach this issue, both traditional and innovative approaches have been used. Troughout this Ph.D. thesis, an accurate and laborious sampling allowed to analyse Parmigiano Reggiano cheese in all stages of manufacturing and through two years of ripening. Traditional microbial counts have been attended and compared with data obtained by means of innovative counting media and direct enumeration considering even cell viability. Cell autolysis has been also evaluated by direct microbial count and by the quantification of both cell lysis-released DNA and cell lysis-released enzymes. Moreover, length heterogeneity-PCR has been held to monitor microbial species evolution during a complete cheesemaking process. Furthermore, a mathematical model able to assess the effect of NaCl concentration, as well as pH and temperature on aminopeptidases activities has been performed.