Botrytis cinerea infection of grapes can cause various problems in winemaking. One of these problems is the loss of the red wine colour. This can be attributed to the laccase enzyme secreted by the fungus into the grapes, which is then present in the grape juice and wine. Laccase is a polyphenol oxidase enzyme that can oxidase several wine substrates, including anthocyanins. Various studies have reported on the effects of laccase on white wine colour, but less is known on the impact of laccase on anthocyanins specifically. This study aimed to investigate this effect and the possible protective effects of oenological tannins and glutathione against the loss of red wine colour.
Researchers analysed the effects of laccase on five different anthocyanins individually and together in a grape juice-like solution. They also investigated the protective effects of grape seed tannins, (-)-epicatechin and glutathione against the loss of red wine colour.
Figure 1: The visual aspect of the five different grape anthocyanins (300 ꙡM) at the beginning of the experiment and after 24 hours of laccase action. CYA: Cyanidin-3-O-G; PEO: Peonidin-3-O-G; DEL: Delphinidin-3-O-G; PET: Petundin-3-O-G; MAL: Malvidin-3-O-G.
Figure 2: Influence of the supplementation with seed tannins, (-)-epicatechin or glutathione on the degradation kinetics of a mixture of the five different grape anthocyanins by the action of laccase.
Figure 3: The visual aspect of anthocyanin samples after 24 hours in the absence or presence of 2 UA of laccase activity/mL. A: Without Laccase; B: With laccase; I: Control; II: seed tannins; III: (-)-epicatechin; IV: glutathione.
The results clearly show laccase’s devastating effect on red wine colour. Tested separately, it seems Peonidin-3-O-G is resistant to laccase action. However, this resistance disappears when all five anthocyanins are present in more real juice-like conditions. This is most likely because peonidin-3-O-glucoside can polymerise with the quinones formed by the oxidation of the other anthocyanins.
Seed tannin, (-)-epicatechin and glutathione had some protective effects against oxidation, with seed tannin being the most effective. However, (-)-epicatechin also caused the formation of brown pigments, which is not ideal for preserving red wine colour.
Winemakers are advised to contact their suppliers of oenological tannins when receiving red grapes infected with Botrytis. Suppliers sell various types of oenological tannin products. To preserve red wine colour as much as possible, the product with the highest percentage of grape seed tannins should be used. Be advised that of all the oenological tannins available, gape seed tannins are the most expensive to produce.
Giménez, P., Just-Borràs, A., Gombau, J., Canals, J. M., & Zamora, F. (2023). Effects of laccase from Botrytis cinerea on the oxidative degradation of anthocyanins. OENO One, 57(3), 243–253. https://doi.org/10.20870/oeno-one.2023.57.3.7567
The figures in this article have been republished in their original form as they appear in OENO One, as permitted by the Creative Commons License of the journal. Their numbers have been changed to fit the format of this article.