Candida zemplinina can reduce acetic acid produced by Saccharomyces cerevisiae in sweet wine fermentations

In this study we have investigated the possibility of using Candida zemplinina, as a partner of Saccharomyces cerevisiae, in mixed fermentations of must with a high sugar content, in order to reduce its acetic acid production. Thirty five C. zemplinina strains, which were isolated from different geographic regions, were molecularly characterized and their fermentation performances were determined. Five genetically different strains were selected for mixed fermentations with S. cerevisiae. Two types of inoculation were carried out: co-inoculation and sequential inoculation. A balance between the two species was generally observed for the first 6 days, after which C. zemplinina started to decrease. Relevant differences were observed concerning the consumption of sugars, the ethanol and glycerol content and acetic acid production, according to which strain was used and which type of inoculation was performed. Sequential inoculation led to reduction of about a half of the acetic acid content, compared to the pure S. cerevisiae fermentation, but the ethanol and glycerol amounts were also low. A co-inoculation with selected couples of S. cerevisiae and C. zemplinina resulted in a decrease of about 0.3 g/L of acetic acid, maintaining high ethanol and glycerol levels. This study demonstrates that mixed S. cerevisiae and C. zemplinina fermentation could be applied in sweet wine fermentation to reduce the production of acetic acid, connected to the S. cerevisiae osmotic stress response.