Impact of Botrytis on the characteristics and foaming properties of yeast macromolecules released during a model juice fermentation

Abstract

Botrytis cinerea is an important fungal pathogen particularly dreaded in cool climate vineyards. It is responsible for important damage, including the decrease in foamability of sparkling wines, such as Champagne. Proteins are largely involved in the stabilization of Champagne foam despite their low concentration. Other works demonstrated changes in must proteins originating from botrytized grapes. Nevertheless, we have very few information concerning the effect of Botrytis contamination on the biochemical and physico-chemical characteristics of proteins released by Saccharomyces during fermentation. To answer this, the proteolytic activity of a Botrytis supernatant was compared with that of a Chardonnay grape juice produced with bunches contaminated by Botrytis (10%, visual estimation). A synthetic must was inoculated with an enological yeast (strain 18-2007, used as a reference) and with strains presenting or not a cell wall mutation with or without 1% of Botrytis culture supernatant. Macromolecule fractions of the 6 wines obtained after alcoholic fermentations were purified and analyzed by SEC-MALLS, and SDS-PAGE (AgNO3 and PAS staining). Mannoproteins and total proteins were quantified by HPLC and by the Bradford method respectively. Finally, the foamability of the wines was measured to estimate the effect of Botrytis proteases on wine foam-active macromolecules. Results show a strong decrease of wine foamability when synthetic musts are inoculated with only 1% (v/v) of Botrytis culture. The MW distribution, the total protein and glycoprotein contents prove a strong degradation of the higher MW molecules released by Saccharomyces during fermentation. Mn, Mw and Hw decrease whilst Mw/Mn, the 1-500.103 g/mol fraction and MPs content (including high, medium and low MW fractions) increase. Nevertheless, no effect of cell wall mutation was observed. This study clearly shows that Botrytis is not only capable to degrade the grape proteins but also the yeast ones, with the deleterious effects on the sparkling wine foaming properties.