Screening of Saccharomyces cerevisiae and Torulaspora delbrueckii strains in relation to their effect on malolactic fermentation

The use of Torulaspora delbrueckii in the alcoholic fermentation (AF) of grape must is increasingly studied and used in the wine industry. In addition to the organoleptic improvement of wines, the synergy of this yeast species with the lactic acid bacterium Oenococcus oeni is an interesting field of study. In this work, 60 strain combinations were compared: 3 strains of Saccharomyces cerevisiae (Sc) and 4 strains of Torulaspora delbrueckii (Td) in sequential AF, and four strains of O. oeni (Oo) in malolactic fermentation (MLF). The objective was to describe the positive or negative relationships of these strains with the aim of finding the combination that ensures better MLF performance. In addition, a new synthetic grape must has been developed that allows the success of AF and subsequent MLF. Under these conditions, the Sc-K1 strain would be unsuitable for carrying out MLF unless there is prior inoculation with Td-Prelude, Td-Viniferm or Td-Zymaflore always with the Oo-VP41 combination. However, from all the trials performed, it appears that the combinations of sequential AF with Td-Prelude and Sc-QA23 or Sc-CLOS, followed by MLF with Oo-VP41, reflected a positive effect of T. delbrueckii compared to inoculation of Sc alone, such as a reduction in L-malic consumption time. In conclusion, the obtained results highlight the relevance of strain selection and yeast-LAB strain compatibility in wine fermentations. The study also reveals the positive effect on MLF of some T. delbrueckii strains.