Influence of raw milk microflora on the characteristics of Swiss-type cheeses. / Evolution of microflora during ripening and characterization of facultatively heterofermentative lactobacilli

Abstract

During the ripening of raw milk 8wiss-type minicheeses, the microbial ecosystem changed, and the quantitative and qualitative levels of microflora evolved constantly. The starter lactic acid bacteria population, ie, thermophilic streptococci and thermophilic lactobacilli, decreased regularly from 10 8 to 10 5 cfu/g. The propionibacteria and the facultatively heterofermentative lactobacilli, which were in very low numbers before ripening, increased rapidly to reach their final level after 6 weeks (approximately 10 8 cfu/g). The other microflora (Micrococcaceae and enterococci) remained at a subdominant level, or were even undetectable during ripening (coliforms, spores of butyric acid bacteria). Indigenous microflora enumerated in microfiltered milk cheeses evolved identically, except that they started at a lower level. Moreover, the starter bacteria decreased faster. Facultatively heterofermentative lactobacilli seemed to be the most important non-starter lactic acid bacteria. Eighty-eight colonies were isolated on FH agar du ring ripening, and characterized by means of the API system. The species identified evolved from a great diversity in the beginning to Iwo major subspecies: L paracasei subsp paracasei 1 and 3. However, the method used to detect this microflora did not allow us to evaluate the nature of the subdominant lactobacilli, although certainly many other species could be isolated.