In this research some potential sources of occurrence of dairy propionibacteria (PAB) in milk were analysed. 115 strains were isolated from raw milk, acid whey, cheese and feed flour samples. As determined by genetic fingerprinting methods and physiological tests, Propionibacterium freudenreichii and P. jensenii were the species most numerous in all the analysed sources. The development ability of single PAB strains in conditions similar to the cheese environment was evaluated. Propionibacterium freudenreichii was the most heat resistant species and comprised strains with tendency to autolysis. Conversely, P. jensenii, P. acidipropionici and P. thoenii remained at high levels throughout the incubation time both in the control medium and in presence of NaCl. PAB isolates showed differences in rate and amount of CO 2 production. Antimicrobial activity against Lactococcus lactis subsp. cremoris LMG 7951 was investigated for all strains; 30% of them was able to inhibit such micro-organism, however only for two strains of P. thoenii the active molecule was probably a bacteriocine.
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