Today there is an increasing interest toward the reduction of ethanol content in wines. Indeed, the impact of climate change upon the global production of grapes and the current demand of well-structured and high phenolic content wines determine a generalized increase of ethanol concentration of wines. Among the various methodologies proposed for the reduction of alcohol content in wine, the microbiological approach seems quite promising to avoid negative variations to the final wine composition. In this regard, Saccharomyces cerevisiae, the main yeast species responsible for alcoholic fermentation during winemaking, is not the best yeast species for reducing alcohol levels in wine. On the other hand, non-Saccharomyces yeast species have shown great potential to produce less ethanol content in wine. Indeed, non-Saccharomyces yeast can divert carbon away from ethanol production affecting ethanol yield, fermentation efficiency, biomass production and final by-products. In addition, respiro-fermentative regulatory mechanisms exhibited by some non-Saccharomyces yeasts (Crabtree negative) are different from that exhibited by S. cerevisiae (Crabtree positive). This metabolic behaviour can be exploited to reduce ethanol production through partial and controlled aeration of the grape juice.
In the present work researchers evaluated the use of M. pulcherrima in sequential fermentations (M. pulcherrima/S. cerevisiae) at different aeration conditions to reduce the alcohol content and maintaining, at the same time, a good aromatic profile of wine. Sequential fermentation allows to exploit the metabolism of non-Saccharomyces yeast while the immobilization procedure allows for high density of cells.
In a preliminary screening the best conditions regarding free/immobilized cells, static/aerated fermentation and inoculation level were identified. Bench-Top fermentation trials with different aeration conditions showed that the use of M. pulcherrima selected strain with aeration flow of 20 mL/L/min during the first 72 h of fermentation, led an ethanol reduction of 1.38% (v/v) in comparison with Saccharomyces cerevisiae control strain. The analytical profile of the resulting wines did not show any negative feature. Indeed, the concentration of ethyl acetate, that above its sensory threshold impacts negatively the wine sensory profile, was found at an acceptable level. On the other hand, an increase in the concentration of significant fruity and flower compounds was found.
SIGNIFICANCE OF THE STUDY:
The study, as many studies before, demonstrated the ability of non-Saccharomyces yeasts to deliver a lower alcohol yield in sequential inoculations than S. cerevisiae on its own.
Canonico, L.; Comitini, F.; Ciani, M. Metschnikowia pulcherrima Selected Strain for Ethanol Reduction in Wine: Influence of Cell Immobilization and Aeration Condition. Foods 2019, 8, 378.
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