WINETECH Technical Yearbook 2021

WHAT THE LATEST RESEARCH SAYS A study by Osete-Alcaraz et al . in 2020 aimed to determine the optimal form of addition of these enzymes for deconstructing the polysaccharide-tannin association in the grape cell wall. But first, they needed to determine whether the grape tannins already in solution could somehow inhibit the action of any added enzymes on the cell wall. The result was conclusive: the enzymes function so quickly by breaking down the cell wall that any tannins in solution could not interfere. This paved the way to determine what the best approach for adding enzymes is, namely individually, together or sequentially. The findings showed that when pectin- lyase and polygalacturonase (both members of the broader family of pectinases) are added to artificial grape must individually, or sequentially, their action is effective to a certain degree. But when added to the must together, a significant increase in the content of tannins released into solution is observed. These enzymes attack the polysaccharide- pectin associations with tannins in grapes, and when working together, they efficiently free the tannins from clutches of the cell wall through pore formation and pectin-

SUMMARY

linkage breakdown. However, if the pectin molecules contain methyl groups (which on average 70% of grape pectin does) the activity of polygalacturonase is limited and another enzyme, pectin methylesterase (another member of the pectinase family) is necessary to remove the methyl groups. In the study, these enzymes also prevented the free tannins from re-joining with polysaccharides already in solution, which is good news as we can expect the improved colour, aroma and mouthfeel that we’re after. When this combination of pectinase enzymes is incorporated into a maceration regime along with other maceration enzymes, the results can be impressive. There is an increased release of polyphe­ nols from the grape cell wall along with a decrease in tannin-polysaccharide associations reforming in solution. This is good news since you can expect improved aromas and mouthfeel, and an emphasis on bolder, more stable colour. The growing topic of maceration enzymes is continuously providing new and advantageous strategies for producing fragrant, bolder and more complex wines. Through careful selection of pectinase enzymes, every red wine will have its chance to glow!

At the time of writing, the author of this article was an Honours student at the Department of Viticulture and Oenology, Stellenbosch University. This article forms part of a science communication assignment where students were tasked to write a popular article based on a recently published scientific article. REFERENCES Claus, H. & Mojsov, K., 2018. Enzymes for wine fermentation: Current and perspective applications. Fermentation 4, 1-19. Kennedy, J.A., Saucier, C. & Glories, Y., 2005. Grape and wine phenolics: History and perspective. ASEV Phenolics Imp. 1, 1-10. Osete-Alcaraz, A., Gómez-Plaza, E., Martínez- Pérez, P., Weiller, F., Schückel, J., Willats, W.G.T., Moore, J.P., Ros-García, J.M. & Bautista-Ortín, A.B., 2020. The impact of carbohydrate-active enzymes on mediating cell wall polysaccharide-tannin interactions in a wine-like matrix. Food Research International 129, 1-9.

Polyphenols are crucial contributors to wine astringency, colour and flavour. Tannins are phenolic compounds involved in wine stabilisation that contribute to mouthfeel attributes and complexity through bitterness and astringency. These tannins have a stabilising function for the anthocyanin colour compounds in red wine, which are extremely sensitive to degradation. The same association of tannins with anthocyanins that preserves colour, also limits the tannin transfer from grape skin and seeds to the wine during maceration. To improve tannin extraction, enzyme preparations are utilised to assist in releasing tannins from polysaccharides in the cell wall. Recent research has evaluated the optimal addition of these enzymes to prevent tannin-polysaccharide associations from occurring during winemaking. The findings showed that when the pectinase enzymes pectin-lyase and polygalacturonase are added to the wine individually or sequentially, their action is limited. But when these two enzymes are added to the must together, the highest release of tannins into solution is observed.

For more information, contact James Duncan at dugald@sun.ac.za.

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