Abstract
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.
Highlights
Several Saccharomyces species have been extensively used in wine making, sake making, and brewing processes such as in bioethanol production, despite yeasts are rather sensible to ethanol accumulation in the reaction medium [1]
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
The ability shown by Saccharomyces spp. to metabolise the hexoses depends on the temperature and the composition of culture media [10,11]
Summary
Several Saccharomyces species have been extensively used in wine making, sake making, and brewing processes such as in bioethanol production, despite yeasts are rather sensible to ethanol accumulation in the reaction medium [1]. The increase in alcoholic fermentation rate by the addition of selected yeasts strains to the must could result ineffective so the residual sugars were utilized by contaminating microorganisms able to carry out unwished metabolic pathways. Such an example, in these conditions, some heterofermentative lactic acid bacteria strains could significantly increase volatile acidity inducing a remarkable loss of quality of the alcoholic beverage. Yeasts lysis, occurring at the end of alcoholic fermentation, determines the solubilisation of cellular contents which can greatly stimulate Brettanomyces spp. growth [5]
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