FUNGAL CHITOSAN IS AN EFFICIENT ALTERNATIVE TO SULPHITES IN SPECIFIC WINEMAKING SITUATIONS

Abstract

The most common method to prevent or eliminate microbes in wine is sulfur dioxide (SO₂) addition. However, as risk of acute allergy exists, the European Union has classified SO₂ as one of the 14 priority food allergens (EU Regulation N°1169/2011, Annex II). The legal dose admitted in both conventional and organic farming will be downgraded probably in the near future, according to consumer’s expectations. In addition, sulfur dioxide addition does not always prevent microbial spoilage, because of the emergence of tolerant/resistant strains. Winemakers thus need alternate and efficient antiseptic methods to reduce total SO₂ content in wines. The resolutions of the 7th general assembly of the International Organization of Vine and Wine (OIV/OENO 338A/2009) and the European Union (EC 53/2011) authorized the addition of fungal chitosan to reduce spoilage microorganism populations especially Brettanomyces bruxellensis. Chitosan is a partially acetylated polysaccharide of glucosamine. It is positively charged at wine pH, which allows it to interact with the microorganisms and particles present in the wine. With the trend in oenology of limiting SO₂, more and more questions arise as to the impact of fungal chitosan on other microorganisms from grapes and wine-related environment. It was shown recently that most species were affected, at least transiently, by chitosan treatment (Miot-Sertier et al. 2022). However, a high variability prevails within most species and sensitive, intermediate and tolerant strains can be observed, as well as different efficiencies depending on the wine chemical parameters or the winemaking stage when the treatment is performed.

In order to have a clear opinion on the usefulness of a chitosan treatment, we have carried out tests in various situations in which sulphites were not enough to protect the wine (presence of tolerant strains in particular). Though chitosan does not solve all the microbial spoilage issues, this study reveals that chitosane can be an interesting alternative to sulphites in certain situations. Furthermore, when the antiseptic effect is clear it seems durable and hence, wines are protected for microbial spoilage over long periods.
The study also shows that structural differences among fungal chitosans impact their efficiency. The organoleptic consequences of the treatment are also evaluated on red and white wines.