Abstract
Brettanomyces bruxellensis is the main spoilage microbial agent in red wines. The use of fungal chitosan has been authorized since 2009 as a curative treatment to eliminate this yeast in conventional wines and in 2018 in organic wines. As this species is known to exhibit great genetic and phenotypic diversity, we examined whether all the strains responded the same way to chitosan treatment. A collection of 53 strains of B. bruxellensis was used. In the conditions of the reference test, all were at least temporarily affected by the addition of chitosan to wine, with significant decrease of cultivable population. Some (41%) were very sensitive and no cultivable yeast was detected in wine or lees after 3 days of treatment, while others (13%) were tolerant and, after a slight drop in cultivability, resumed growth between 3 and 10 days and remained able to produce spoilage compounds. There were also many strains with intermediate behavior. The strain behavior was only partially linked to the strain genetic group. This behavior was little modulated by the physiological state of the strain or the dose of chitosan used (within the limits of the authorized doses). On the other hand, for a given strain, the sensitivity to chitosan treatment was modulated by the chitosan used and by the properties of the wine in which the treatment was carried out.
Highlights
The most feared microbial spoilage in red wines is volatile phenols accumulation, associated with the development of the yeast Brettanomyces bruxellensis (Chatonnet et al, 1992; Romano et al, 2009; Comitini et al, 2019)
F4 was chosen to examine the importance of the codex requirement for chitosan activity in wine
Superimposition of two phenomena may contribute to chitosan final efficiency for a given strain present: a masking of chitosan active fraction by steric hindrance or linking to wine compounds, which may decrease chitosan efficiency, and a direct effect of the wine composition and characteristics on yeast growth inhibition, which may indirectly contribute to higher chitosan efficiency. This is the first study to report the characterization of chitosan impact on B. bruxellensis that takes into account the genetic factor (53 tested strains representative of the great genetic diversity of the species), the impact of the wine matrix and the impact of the chitosan batch
Summary
The most feared microbial spoilage in red wines is volatile phenols accumulation, associated with the development of the yeast Brettanomyces bruxellensis (Chatonnet et al, 1992; Romano et al, 2009; Comitini et al, 2019). Phenol deviations constitute a criterion for systematic rejection, tarnish the product image and turn buyers away, often permanently. They are perceived by professionals and by consumers, all over the world (Curtin et al, 2007). The most common method to prevent or eliminate B. bruxellensis in wine is sulfur dioxide (SO2) addition (Barata et al, 2008). The use of SO2 can cause undesirable odors of sulfur, hydrogen sulfide formation, and consumption of sulfites causes headaches in many people.
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