Introduction:
The production of wine involves a complex process that includes the growth of yeast and bacteria, which are responsible for the fermentation of grape juice into wine. However, the growth of these microorganisms can also lead to spoilage and other quality issues in wine. Therefore, it is essential to find effective ways to control the growth of wine microbes without affecting the quality of the wine.
Due to its antimicrobial properties, sulphur dioxide (SO2) is currently the most used preservative. However, natural antimicrobial agents in the food and beverage industry are gaining increasing attention to reduce reliance on preservatives such as SO2 and provide safer and healthier consumer products. As the demand for natural and organic food and beverage products continues to grow, developing effective and sustainable antimicrobial agents is critical for the success and sustainability of these industries.
One potential solution for wine is fungal chitosan, a natural polysaccharide derived from chitin. The use of chitosan as a preservative in winemaking has several potential advantages. Unlike sulphur dioxide, a chemical preservative, chitosan is a natural product derived from a renewable source. Chitosan is also biodegradable, so it does not accumulate in the environment like many chemical preservatives. Furthermore, chitosan has been shown to have antimicrobial properties against a wide range of wine microorganisms, which makes it a promising alternative to traditional preservatives.
Legislation and supply:
The Official Journal of the European Union (2019) authorises the use of chitosan from fungal origin for:
- Fining of must to facilitate settling and reduce protein haze
- Fining of wine to reduce turbidity and reduce protein haze
- Removal of heavy metals
- Removal of contaminants such as Ochratoxin A
- Removal of undesirable microorganisms, notably Brettanomyces
Chitosan is also authorised for use in South Africa, and as a result, various suppliers have chitosan-based products on the market. Supply offerings include commercial names such as OenoBrett and BactiControl from Laffort, No Brett Inside from Lallemand, and Enartisstab Micro M and Claril M from Enartis. Suppliers market these products based on the applications as permitted by the EU, and depending on the application, chitosan can form part of a blend of oenological products to deliver a synergistic effect. Most suppliers market their chitosan products as part of a strategy to lower the use of SO2 in winemaking.
Regarding the objective of removing undesirable microorganisms, suppliers market their products as effective against various yeasts, including Brettanomyces as well as acetic acid bacteria (AAB) and lactic acid bacteria (LAB).
What the science says about bacterial inhibition:
Various scientific publications have demonstrated the effect of chitosan against Brettanomyces and LAB. However, there seems to be a discrepancy in chitosan’s efficacy in inhibiting AAB. A study by Valera and co-workers (2017) found chitosan from a specific supplier effective against two Acetobacter strains: Acetobacter pasteurianus and Acetobacter malorum. It reduced the population quantity and metabolic activity compared to controls and was as effective as SO2. These were the only two species they tested. Therefore, this chitosan may be effective against more strains, or maybe not. A more recent study by Miot-Sertier and co-workers (2022) tested the effect of two different chitosans on 206 wine microbes: 34 Saccharomyces strains, 56 Brettanomyces strains, 29 non-Saccharomyces strains, 33 Oenococcus oeni strains, 43 other LAB and 11 AAB strains. The AAB strains included the following species:
- Acetobacter aceti (2)
- Acetobacter pasteurianus (4)
- Gluconobacter hanseni (2)
- Gluconobacter oxydans (3)
These are some of the results obtained in the study:
- Chitosan treatment was not effective against AAB species.
- Chitosan treatment was not effective against the spoilage non-Sacch yeast, Hanseniaspora uvarum (mainly found during the pre-fermentative stages of winemaking).
- Chitosan treatment was very effective against LAB and the onset of malolactic fermentation (MLF).
- Saccharomyces cerevisiae was not affected by chitosan. Prevention of sweet wine re-fermentation with chitosan is thus not possible.
- Brettanomyces strains showed different sensitivity levels towards treatment depending on the wine. Elimination is possible.
- The lower molecular weight chitosan that complies with OIV regulation and specifications was much more efficient than the higher molecular weight chitosan it was compared with.
Thus, chitosan can solve some oenological issues related to microorganisms, but its effectiveness depends on the wine and the microorganism targeted. This can explain why some studies have contradictory findings. This is the case for the two mentioned studies’ results for AAB. Either way, chitosan seems to be an effective tool to prevent microbial spoilage after alcoholic fermentation and forms part of a strategy to lower the use of SO2 in wine.
Further studies are needed to determine the maximum dosage of chitosan and its effect on the microbial stability period of the wine after treatment.
References:
- Lárez Velásquez, C. (2023). Chitosan and its applications in oenology. OENO One, 57(1), 121–132. https://doi.org/10.20870/oeno-one.2023.57.1.7262
- Miot-Sertier, C., Paulin, M., Dutilh, L., Ballestra, P., Albertin, W., Masneuf-Pomarède, I., Coulon, J., Moine, V., Vallet-Courbin, A., Maupeu, J., Dols-Lafargue, M. (2022). Assessment of chitosan antimicrobial effect on wine microbes. International Journal of Food Microbiology, 381, 109907. https://doi.org/10.1016/j.ijfoodmicro.2022.109907
- Valera, M.J., Sainz, F., Mas, A., Torija, M.J. (2017). Effect of chitosan and SO2 on viability of Acetobacter strains in wine. International Journal of Food Microbiology, 246, 1-4, https://doi.org/10.1016/j.ijfoodmicro.2017.01.022
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