Malolactic fermentation performance of indigenous Oenococcus oeni strains from Shaanxi wine region (China) and their mutants on Pinot Noir and Chardonnay wines

This study investigated the malolactic fermentation (MLF) performance of three indigenous Oenococcus oeni strains isolated from the Shaanxi wine region (China) and mutants of those strains with different acid-tolerant phenotypes on Pinot Noir and Chardonnay wines. The MLF kinetics of these strains, as well as the basic chemical parameters and volatile compounds of wines after MLF, were determined. All strains successfully completed MLF in Pinot Noir wines with a pH of 3.45; however, only the acid-tolerant mutants were able to complete MLF in Chardonnay wines with a pH of 3.2. Compared with other strains, inoculation with the acid-tolerant mutants reduced the MLF duration up to 4.5 days in Pinot Noir wines, and significantly increased the concentrations of total volatile compounds in Pinot Noir wines and Chardonnay wines, with values rising from 324226.38 to 361450.91 μg/L and from 213322.96 to 279848.12 μg/L, respectively. These wines had higher levels of 2,3-butanediol, linalool, α-terpineol and β-damascenone, contributing to more pronounced butter and floral aroma profiles. MLF performance of these strains was positively correlated with their acid tolerance, and indigenous acid-tolerant mutants show great potential to be developed as MLF starters, contributing to the regional characteristics and high quality of wines.