Typical metabolic traits of two Oenococcus oeni strains isolated from valpolicella wines

Aims: Physiological comparison of two indigenous Oenococcus oeni strains, U1 and F3 isolated in the same area (Valpolicella, Italy) in order to select a performant starter for MLF in wine. Methods and Results: Growth rate, sugar and malate metabolism in FT80 media at pH 5.3 and 3.5 were analysed. The amount of total protein synthesized and the level of expression of the small Hsp Lo18 were evaluated by radiolabelling and immunodetection experiments after heat (42°C), acid (pH 3.5) and ethanol (12% v/v) stresses. Strain U1 showed significantly lower specific growth rate and growth yield in acid conditions than strain F3. However, strain Ul had a higher malate consumption capacity at pH 3.5 than strain F3, in relation with an higher malolactic activity determined on whole cells. Strain Ul exhibited about half the total protein synthesis level than strain F3, but both strains expressed Lo18 similarly. Evaluation of malolactic fermentation (MLF) performance by microvinification trials was carried out. Strain Ul was able to complete MLF, whereas strain F3 degraded malic acid partially when inoculated in Amarone wine. Conclusions: Considering its performances in microvinifications experiments, strain U1 could be a good candidate for malolactic starter as an alternative to deficient commercial starters.