Kinetics and malolactic activity of Oenococcus oeni strains sequentially inoculated in yeast fermented broth

MENDOZA L.M.; FARÍAS M.E.

Tucumán, Argentina

Simposio; III Simposio Internacional de Bacterias Lácticas. II Encuentro Red BAL Argentina.; 2009

Malolactic fermentation is a fundamental biochemical reaction in wine making, occurring at the end of alcoholic fermentation, when bacteria convert malic acid into lactic acid and carbon dioxide. Oenococcus oeni is the most important species among bacteria involved in MLF. Many strains of this species are well adapted to survive and grow in wine. Moreover, the viability of O. oeni in wine is strictly dependent on the capacity of this bacterium to tolerate multiple physical stresses such as acidity, SO2, high concentrations of ethanol and other inhibitory metabolites produced by wine yeasts. The main of this work was to evaluate the modification of growth and malic acid metabolism of different strains of O. oeni in fermented media by Saccharomyces cerevisiae. The wine yeast was cultured in grape juice medium for 6 days at 25ºC and the supernatant was used as fermented medium for sequential inoculation of malolactic bacteria. Unfermented grape juice medium was used as control. To avoid bacterial inhibition caused by depletion of nutrients, all media were supplemented with a concentrated solution of MRS components. Seven strains of O. oeni isolated from Cafayate wine and a commercial strain, PSU-1, were inoculated in fermented media with 107 cells ml-1. The bacterial growth was monitored by OD560nm. Concentration of L-malic acid was determined enzymatically. The growth of all strains of O. oeni was inhibited in fermented media by S. cerevisiae. The strains X2L and 21 were the most sensitive to the metabolites produced by the wine yeast whereas O. oeni m showed the lowest inhibition by S. cerevisiae. In unfermented media the malic acid depletion was similar among the several strains of O. oeni. However, in yeast fermented media, the specific malic acid consumption rate of O. oeni strains m, X2L, 10 and 49 increased, being similar for strains ST and PSU-1. The remaining strains, showed lower demalication rate in regard to control. Also, these strains were characterized by the lowest consumption rate, 0.07 and 0.16 g h-1(g dry weight)-1 for strains 21 and 29, respectively. The results highlight that the antagonistic effect of wine yeast on O. oeni growth was strain dependent and this effect did not necessarily prohibit MLF. During the sequential inoculation simulating the natural process of winemaking, the bacteria reached less biomass, but successfully completed the MLF. This study showed the importance to understanding interaction between S. cerevisiae and O. oeni to control this aspect of wine ecology by choosing a particular yeast and bacteria pair