Changes in the microbiological and physicochemical characteristics of Serrano cheese during manufacture and ripening

Abstract

Changes in the microbial flora present in six Serrano cheese batches (3 ripened in Summer and 3 in Winter) were studied during production and ripening, to microbiologically characterize this cheese, which is traditionally manufactured by farmers in the south of Brazil, using raw cow milk, without the addition of starter cultures. The levels of several microbial groups were enumerated in the milk, curd and different stages of the 60-day long ripening period. Values of some physicochemical parameters, such as pH, titratable acidity, water activity, moisture and NaCl content were also determined. The correlation coefficients between these parameters and the microbial groups throughout ripening were determined. The influence of the season of the year was also studied. Results demonstrated that the microflora and the physicochemical characteristics of Serrano cheese changed significantly during the 60-day ripening period, especially in Summer. Almost all microbial groups reached their highest counts after the 7th day of maturation, steadily decreasing towards the end of the process. Higher microbial counts during the first week of ripening was accompanied by lactic acid production and, as a consequence, a sharp drop in the pH of cheese was observed. Lactic acid bacteria comprised the main microbial group present in Serrano cheese and their counts were similar to the total viable counts at all sampling points. The abundance of lactobacilli during the manufacture and ripening suggests that these microorganisms may play an important role in the production of Serrano cheese. In conclusion, this work shows the importance of ripening time being longer than 30 days to allow for microbiological stabilization of this artisanal product. Also, except for halotolerants and moulds counts, and for moisture content, there were no significant differences observed either for microbial counting or for physicochemical characteristics of the cheese concerning the season of the year in which the product was manufactured.