Interactions between Torulaspora delbrueckii and Saccharomyces cerevisiae in wine fermentation: influence of inoculation and nitrogen content

Alcoholic fermentation by an oenological strain of Torulaspora delbrueckii in association with an oenological strain of Saccharomyces cerevisiae was studied in mixed and sequential cultures. Experiments were performed in a synthetic grape must medium in a membrane bioreactor, a special tool designed to study indirect interactions between microorganisms. Results showed that the S. cerevisiae strain had a negative impact on the T. delbrueckii strain, leading to a viability decrease as soon as S. cerevisiae was inoculated. Even for high inoculation of T. delbrueckii (more than 20x S. cerevisiae) in mixed cultures, T. delbrueckii growth was inhibited. Substrate competition and cell-to-cell contact mechanism could be eliminated as explanations of the observed interaction, which was probably an inhibition by a metabolite produced by S. cerevisiae. S. cerevisiae should be inoculated 48 h after T. delbrueckii in order to ensure the growth of T. delbrueckii and consequently a decrease of volatile acidity and a higher isoamyl acetate production. In this case, in a medium with a high concentration of assimilable nitrogen (324 mg L-1), S. cerevisiae growth was not affected by T. delbrueckii. But in a sequential fermentation in a medium containing 176 mg L-1 initial assimilable nitrogen, S. cerevisiae was not able to develop because of nitrogen exhaustion by T. delbrueckii growth during the first 48 h, leading to sluggish fermentation.