Enzymes involved in flavour formation by bacteria isolated from the smear population of surface‐ripened cheese

Twenty‐five bacterial isolates recovered from the surface population of smear‐ripened cheese were assigned phenotypically asBrevibacteriumspp., Corynebacteriumspp. andAureobacteriumspp. using the Biolog GP2 microplate system and database. The range and activity of hydrolytic enzymes involved in the formation of cheese flavour constituents were monitored in cell‐free lysates of the isolates. Esterase activity and the presence of a range of enzymes involved in amino acid release and breakdown was confirmed in all strains examined although there were pronounced interspecies and strain differences in the level of activity detected. Peptidolytic activities present in the smear bacteria included dipeptidyl peptidase and aminopeptidases that cleaved various N‐terminal amino acids including proline. Subsequent breakdown of the released aromatic and branched‐chain amino acids was mediated by α‐keto acid dependent aminotransferase action and several of the isolates were able to form thiols from sulphur‐containing amino acid precursors. It was confirmed that the enzymic activity of the smear population could be manipulated by the use of defined starter cultures comprising selected combinations of smear isolates. The hydrolytic activities of the smear bacteria are involved in the generation of cheese flavour compounds and the enzyme profile is thus an important selection criterion for strains to be evaluated for use in defined surface smear preparations.