Growth and aroma contribution of Microbacterium foliorum, Proteus vulgaris and Psychrobacter sp. during ripening in a cheese model medium.

The growth and aroma contribution of Microbacterium foliorum, Proteus vulgaris and Psychrobacter sp., some common but rarely mentioned cheese bacteria, were investigated in a cheese model deacidified by Debaryomyces hansenii during the ripening process. Our results show that these bacteria had distinct growth and cheese flavour production patterns during the ripening process. P. vulgaris had the greatest capacity to produce not only the widest variety but also the highest quantities of volatile compounds with low olfactive thresholds, e.g. volatile sulphur compounds and branched-chain alcohols. Such compounds produced by P. vulgaris increased after 21 days of ripening and reached a maximum at 41 days. The three bacteria studied exhibited various degrees of caseinolytic, aminopeptidase and deaminase activities. Moreover, P. vulgaris had a greater capacity for hydrolysing casein and higher deaminase activity. Our results show that P. vulgaris, a Gram-negative bacterium naturally present on the surface of ripened cheeses, could produce high concentrations of flavour compounds from amino acid degradation during the ripening process. Its flavouring role in cheese cannot be neglected. Moreover, it could be a useful organism for producing natural flavours as dairy ingredients.