Influence of sugars and pH on the citrate metabolism of different lactic acid bacteria strains in a synthetic wine matrix

Aims This study investigated the influence of sugars (glucose and fructose) and pH on the gene expression of citE (citrate lyase beta-subunit) and the subsequent formation of metabolites associated with citrate metabolism. Methods and Results Different levels of glucose (2 center dot 5, 50 and 115 g l(-1)), fructose (2 center dot 5, 50 and 115 g l(-1)) and pH (3 center dot 0, 3 center dot 5, 4 center dot 0 and 5 center dot 0) were evaluated for their effect on citE expression in four different lactic acid bacteria strains. Two Oenococcus oeni strains and two Lactobacillus plantarum strains were used, of which one strain of each species screened positive for the citE gene. Among the factors tested, fructose had the biggest influence on the relative expression of citE in O. oeni. In addition, the citrate-positive strains produced high concentrations of diacetyl and acetoin. Conclusions This study gives an overview of how sugar, pH and different lactic acid bacteria strains influence citE gene expression and the formation of metabolites associated with citrate metabolism closely linked to malolactic fermentation (MLF). Significance and Impact of the Study These results can be used to make informed decisions regarding MLF when aiming to create a wine with a buttery aroma or not.