Field-flow fractionation as analytical technique for the characterization of dry yeast: correlation with wine fermentation activity.

Important oenological properties of wine depend on the winemaking yeast used in the fermentation process. There is considerable controversy about the quality of yeast, and a simple and cheap analytical methodology for quality control of yeast is needed. Gravitational field flow fractionation (GFFF) was used to characterize several commercial active dry wine yeasts from Saccharomyces cerevisiae and Saccharomyces bayanus and to assess the quality of the raw material before use. Laboratory-scale fermentations were performed using two different S. cerevisiae strains as inocula, and GFFF was used to follow the behavior of yeast cells during alcoholic fermentation. The viable/nonviable cell ratio was obtained by flow cytometry (FC) using propidium iodide as fluorescent dye. In each experiment, the amount of dry wine yeast to be used was calculated in order to provide the same quantity of viable cells. Kinetic studies of the fermentation process were performed controlling the density of the must, from 1.071 to 0.989 (20/20 density), and the total residual sugars, from 170 to 3 g/L. During the wine fermentation process, differences in the peak profiles obtained by GFFF between the two types of commercial yeasts that can be related with the unlike cell growth were observed. Moreover, the strains showed different fermentation kinetic profiles that could be correlated with the corresponding fractograms monitored by GFFF. These results allow optimism that sedimentation FFF techniques could be successfully used for quality assessment of the raw material and to predict yeast behavior during yeast-based bioprocesses such as wine production.