A simple method for assaying the aptitude of yeast to adsorb phenolic compounds (intervento orale)

There is a remarkable variability in the adsorption capacity of phenolic compounds by wine yeast strains. Adsorption of phenolic compounds released from grapes is significant, especially in red wine technology. The goal of this research was to develop a new, very simple method for the determination of this capability based on visual evaluation of the colour of yeast colonies. The assumption is that colony colour reflects phenol binding of the biomass. Two new chromogenic plating media were prepared: grape-skin agar (homogenised grape-skin 200 g/L, peptone from casein 7.5 g/L, yeast extract 4.5 g/L, agar 15 g/L) and grape-seed agar (homogenised grape-seed 100 g/L, peptone from casein 7.5 g/L, yeast extract 4.5 g/L, agar 15 g/L). The media were sterilised at 121°C for 15 min, poured into Petri dishes, inoculated with a small quantity of yeast biomass, and incubated at 25°C for 7 days. The biomass colour - ranging from white to dark hazel - was correlated with the varying yeast aptitude to adsorb phenolic compounds: white biomass colour was explained as zero or low adsorption; dark hazel biomass colour as high adsorption. Evident colour differences among the strains were observed; these differences were confirmed by microvinification trials. The present research has shown that it is possible to quickly and simply select wine yeasts regarding their ability to interact with phenolic compounds. This indirect method has the potential to be applied mainly in industrial technology. It notably decreases times and costs of testing, allowing the opportunity to amplify the number of tested strains.