Another important function of chitosan is the removal of metal cations from the solution which, reduces the content of heavy metals such as iron, lead, cadmium and copper. On the one hand, this type of action allows avoiding copper and iron instabilities, on the other, it further destabilizes the microbial cell wall by removing structural cations.

In addition, it reduces any unwanted compounds such as ochratoxin A, a fungal toxin that can be found following microbial alterations in grapes. But what makes chitosan the polysaccharide of choice in oenology is its ability to inhibit Brettanomyces: against these contaminating yeasts, in fact, chitosan serves as an indispensable adjuvant and its use allows achieving incomparable results compared to other products.

The antiseptic action of chitosan against Brettanomyces 

The most important and widespread use of chitosan in oenology relates to the inhibition of Brettanomyces, where no other adjuvant is able to perform such an effective action. Brettanomyces is a contaminating yeast, which is particularly resistant to high levels of ethanol and can catalyze the reduction of vinylphenols through the enzyme vinylphenol reductase. This type of biocatalytic activity is responsible for the onset of olfactory defects such as the scents of “stable”, “leather” and “horse sweat”.

We need to examine the structure of chitosan in order to explain how it acts against the onset of Brettanomyces. Chitosan is obtained from the partial deacetylation of chitin, during which the release of the primary amino groups occurs, which in an acid environment are protonated, and thus yield a positive charge.