Chitosan from sustainable source: antimicrobial activity against undesirable yeasts for production of low-sulphite wine

Abstract

The addition of sulphur dioxide (SO₂) is the method traditionally used for wine stabilisation, due to its broad spectrum of action against unwanted microorganisms and its ability to prevent oxidative phenomena. However, in recent years, interest toward alternatives to SO₂ has grown significantly due to concerns over its negative health effects on sensitive consumers and its impact on wine organoleptic properties (Li et al., 2008). For these reasons, the research has focused on alternative methods to reduce or eliminate the use of SO₂, while maintaining wine microbiological stability (Tedesco et al., 2022). Among the different alternatives proposed, chitosan, a natural polysaccharide obtained from the deacetylation process of chitin, has emerged as a promising SO₂-alternative. The OIV (International Organization of Vine and Wine) has already authorised the use of chitosan extracted from the fungus Aspergillus niger for different oenological purposes. However, other sources of chitin, and consequently of chitosan, are available. The aim of this research activity was to investigate the potential use of an innovative and sustainable chitosan, which is insect-based chitosan, for the control of unwanted wine microorganisms. Insects can be reared on different substrates and can be used for bioconversion of wastes; this allows to obtain the chitin during the whole year with a sustainable process (van Huis, 2013; Scala et al., 2020). Furthermore, the low molecular weight and high deacetylation degree of insect-based chitosan (Triunfo et al., 2022) are characteristics potentially correlated with high antimicrobial activity (Poznanski et al. 2023). The first step of this study was addressed to evaluate the antimicrobial activity of chitosan extracted from three different sources, which were shrimps shells (commercial chitosan), A. niger (chitosan approved for oenological use) and the insect Hermetia illucens, against different non-Saccharomyces species, such as Metschnikowia pulcherrima, Candida zemplinina, Hanseniaspora uvarum, H. guilliermondii, H. osmophila, Torulaspora delbrueckii, Zygosaccharomyces bailii, Lachancea thermotolerans, Pichia kluyveri, P. kudriavzevii, P. anomala. The second step of the research was addressed to evaluate the effect of the three chitosan types against Brettanomyces bruxellensis in comparison to Saccharomyces cerevisiae by flow cytometry, in order to obtain information on cell viability and damage at the cellular membrane level. The aim of this step was to elucidate the mechanism of antimicrobial action of chitosan, which is not yet well understood.

The obtained results showed that the antimicrobial activity is correlated to chitosan source and the effect is species/strain dependant; however, insect-based chitosan resulted very active against B. bruxellensis, promoting itself as an effective alternative to oenological chitosan.