Better understanding on the fungal chitosan and derivatives antiseptic effect on Brettanomyces bruxellensis in wine.

Abstract

The addition of fungal chitosan in wine is allowed since 2009 to release some spoilage microorganisms such as Brettanomyces bruxellensis (OIV/OENO 338A/2009; EC 53/2011). This yeast is able to produce volatile phenols and is responsible of organoleptic deviations compromising quality and typicality of red wines [1]. Despite the fact that fungal chitosan is highly renewable, no toxic and non-allergenic, its use remains marginal because this treatment is relatively recent (compare to sulphites treatment) and information are contradictory between different studies described in literature. For all these reasons, actors of wine industry are cautious to exploit this biopolymer. CHITOWINE project is born in this background to better understand the chitosan’s mechanism of action on Brettanomyces bruxellensis, to improve the effectiveness of this treatment in wine, and to disseminate recommendations among wine makers. Tests of sensitivity of two batches of fungal chitosan with different molecular weight (Mw) and acetylation degrees (DA) (F1, Mw = 30000 Da, DA = 10%; F4, Mw = 400000 Da, DA = 16%) have been done on 53 strains of B. bruxellensis in wine media. Three profiles were distinguished: strains having increased sensitivity (41%), others showed an intermediate profile, and few strains were categorized as resistant to chitosan (13%). At the end of those tests, F1 chitosan showed effectiveness clearly higher than F4 chitosan [2]. To identify the parameters which enhance or decrease the effectiveness of fungal chitosan, chemicals hydrolysis to modulate the molecular weight and chemical acetylation to modulate acetylation degrees were applied on F1 and F4 chitosan batches. Chemicals hydrolyses permitted the achieving of fractions having a molecular weight from 3000 to 100 000 Da. After a chemical acetylation, fractions fully acetylated were generated. Sensitivity to those chitosan derivatives fractions was thereafter evaluated on B. bruxellensis in wine media to establish a link between the structure and the function of chitosan and then, better understand the mechanism of action of this renewable biopolymer