Ethyl butanoate is synthesised both by alcoholysis and esterification by dairy lactobacilli and propionibacteria

Abstract

Esters are important flavour-active compounds in cheese and result from the activity of cheese bacteria. The bacteria and reactions involved, however are still largely unknown, with two main mechanisms, alcoholysis or esterification, potentially involved in ester synthesis from different precursors. The aim of this study was to compare the potential for ester synthesis via different reactions in ripening bacteria. Four strains, one Lactobacillus fermentum, one L. casei, and two Propionibacterium freudenreichii, were tested as growing cultures and cell-free extracts (CFE) for their capacity to synthesise ethyl butanoate (EtC4) in the presence of different precursors. In cultures, EtC4 was mainly produced via alcoholysis. The highest EtC4 levels were produced by L. fermentum. Propionibacteria were also able to synthesise esters via alcoholysis, as demonstrated here for the first time. CFE from L. fermentum synthesised EtC4 via alcoholysis, whereas the other three strains did it via esterification. Our results show that the EtC4 synthesis mechanisms and the amounts produced were markedly strain-dependent, and suggest that both esterification and alcoholysis could be involved in ester formation during cheese ripening. By providing a better understanding of EtC4 biosynthesis, this work paves the way for controlling its production in cheese, accelerating the formation of desirable flavour.