Isolation, selection, and characterization of autochthonous Oenococcus oeni strains according to their oenological properties.

Malolactic fermentation (MLF), carried out mainly by Oenococcus oeni after completion of the alcoholic fermentation, is a desirable microbiological process for certain types of wines. It contributes to the deacidification, microbial stability and aroma complexity of the wine. A common winery practice for MLF induction is the inoculation with commercially available strains. This practice oftentimes results problematic and fermentation is slow, incomplete or actually conducted by autochthonous strains with unpredictable results. The use of a selected autochthonous starter culture, well-adapted to the conditions of a specific wine-producing area, is proposed as alternative to ensure prompt initiation and completion of the fermentation. Grape must of the Vitis vinifera cv. Barbera is a rather harsh environment for O. oeni; low pH and high ethanol concentration after alcoholic fermentation are mainly responsible for MLF failure. For this reason a survey of O. oeni biodiversity was conducted with the purpose of identifying strains adapted to the specific grape must. One hundred and twenty-one strains of O. oeni were isolated during spontaneous MLF of Barbera wines from the Monferrato area (Piedmont, Italy). Fingerprinting analysis using the (GTG)5 primer revealed the existence of sixteen different strains. A thorough physiological characterization of these O. oeni strains was conducted. The main oenological properties considered were tolerance to low pH, high ethanol content and SO2. Subsequently, the seven strains that produced the best results were chosen for further analysis that considered the interaction with the yeast strain responsible for the alcoholic fermentation. This interaction may have a profound influence on the ability of the O. oeni to commence and complete the malolactic fermentation. Three autochthonous yeast strains, previously isolated from Barbera must, were used to conduct alcoholic fermentation in laboratory fermentations. Subsequently, the selected O. oeni strains were inoculated. Three out of the seven strains were able to persist in the must, as documented by the viable counts, and to convert malic acid to lactic acid. The results obtained suggest that the O. oeni intraspecies biodiversity represents a natural resource that can be exploited to improve the MLF process.