Angela Zinnai, Francesca Venturi, Chiara Sanmartin, Gianpaolo Andrich
Over the last two decades, most of Italian vines have produced grapes with higher sugar to total acid ratios, greater concentrations of phenols and aromatic compounds and greater potential wine quality. As a consequence, the musts obtained by these grapes are more difficult to process because of the risk of slowing or stuck of fermentation. With the aim of describing the time evolution of the sugars bioconversion during alcoholic fermentation, the kinetics of the D-glucose and D-fructose degradations, promoted by two yeast strains (Saccharomyces cerevisiae (strain C) e Saccharomyces bayanus (strain B)), was investigated using synthetic media, added or not with ethanol. The concentrations of both the substrates and the products of the sugars conversions, as well as the number of viable cells of yeasts, were determined as a function of the alcoholic fermentation time and the related kinetics constants determined. If the reaction medium contained high concentrations of both glucose and fructose, the strains showed significant different fermentatory ability. In these conditions a stuck of fermentation occurred and the remaining sugar was only fructose (strain C) or prevailing fructose (strain B). If the reaction medium contained only glucose as substrate, the strain C seemed more efficient while the kinetics behavior changed completely in presence of only fructose. On the basis of the information collected using this kinetic approach, it would be possible to develop technical data sheets, specific for each yeast strain, useful to choose the optimal microbial strain as a function of the different operative conditions. Moreover the kinetic constant of hexose conversion could be adopted as bio-markers in selection and breeding of wine yeast strains having a lower tendency for sluggish fructose fermentation.
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