Abstract
BackgroundAerobic fermentation of grape must, leading to respiro-fermentative metabolism of sugars, has been proposed as way of reducing alcohol content in wines. Two factors limit the usefulness of Saccharomyces cerevisiae for this application, the Crabtree effect, and excess volatile acidity under aerobic conditions. This work aimed to explore the impact on ethanol acetate production of different S. cerevisiae strains deleted for genes previously related with the Crabtree phenotype.ResultsRecombinant strains were constructed on a wine industrial genetic background, FX10. All yeast strains, including FX10, showed respiro-fermentative metabolism in natural grape must under aerobic conditions, as well as a concomitant reduction in ethanol yield. This indicates that the Crabtree effect is not a major constrain for reaching relevant respiration levels in grape must. Indeed, only minor differences in ethanol yield were observed between the original and some of the recombinant strains. In contrast, some yeast strains showed a relevant reduction of acetic acid production. This was identified as a positive feature for the feasibility of alcohol level reduction by respiration. Reduced acetic acid production was confirmed by a thorough analysis of these and some additional deletion strains (involving genes HXK2, PYK1, REG1, PDE2 and PDC1). Some recombinant yeasts showed altered production of glycerol and pyruvate derived metabolites.ConclusionsREG1 and PDC1 deletion strains showed a strong reduction of acetic acid yield in aerobic fermentations. Since REG1 defective strains may be obtained by non-GMO approaches, these gene modifications show good promise to help reducing ethanol content in wines.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0555-y) contains supplementary material, which is available to authorized users.
Highlights
Aerobic fermentation of grape must, leading to respiro-fermentative metabolism of sugars, has been proposed as way of reducing alcohol content in wines
The aim was the identification of yeast genetic modification strategies that would improve alcohol level reduction during wine fermentation under aerobic conditions
Given that the Crabtree effect is the major metabolic feature of S. cerevisiae restricting respiratory metabolism, three of these genes were selected according to published information about the impact of gene deletions on respiro-fermentative metabolism
Summary
Aerobic fermentation of grape must, leading to respiro-fermentative metabolism of sugars, has been proposed as way of reducing alcohol content in wines. Wines with a high alcoholic degree might be rejected by some consumers on the ground of health or road safety considerations International trade of such wines might be hampered by significant increases in taxes, depending on the countries involved. Concerning the fermentation step in winemaking, most of the efforts are currently focused on the use of non-Saccharomyces wine yeast species/strains showing lower ethanol yields than Saccharomyces cerevisiae [6, 7]. Several yeast strains were shown to be able to reduce ethanol yields during aerated fermentation, as compared to standard conditions [9]; but many of them, including S. cerevisiae strains, were discarded for this application, due to a significant increase in acetic acid production under aerobic conditions [9, 10]. Volatile acidity due to the metabolic activity of S. cerevisiae would always remain a matter of concern for the fermentation of wine under aerated conditions, as shown in studies using a combination of Metschnikowia pulcherrima and S. cerevisiae [11]
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