NEW METHOD FOR THE QUANTIFICATION OF CONDENSED TANNINS AND OTHER WINE PHENOLIC COMPOUNDS USING THE AUTOMATED BIOSYSTEMS SPICA ANALIZER

Abstract

Wine phenolic compounds are important secondary metabolites in enology due to their antioxidant and nutraceutical properties, and their role in the development of color, taste, and protection of wine from oxidation and spoilage. Tannins are valuable phenolic compounds that contribute significantly to these wine properties, especially in mouthfeel characteristics; however, tannin determination remains a significant challenge, with manual and time-consuming methods or complex methodologies. The purpose of this study is to propose a novel method for quantifying condensed tannins in finished wine products. This method aims to provide an accurate approximation of condensed tannin levels, similar to the widely used precipitation assay that involves the polysaccharide polymer methyl cellulose. The new tannin approximation is based on the strong correlation observed between Total Polyphenol Index (TPI) and methyl cellulose precipitable (MCP) tannin assay as both are determined at 280 nm, and using the epicatechin calibration is possible to obtain a value that is equivalent to condensed tannins determined by MCP tannin assay. Thus far, the results have shown a strong correlation between this new method and MCP tannin assay, with an r2 value of 0.83 and a sample size of 60. The present study has included wines from diverse geographical locations and varying ages. In addition to quantifying condensed tannins, the study also aimed to explore potential correlations that may explain differences found in the wines by analysing other polyphenolic parameters. These parameters included catechins determined via the DMACA reaction, anthocyanins based on their structural transformation arising from a change in pH, total polyphenols measured using the Folin-Ciocalteu reaction, TPI, and the chromatic features of wines at 420, 520 and 620 nm. Moreover, the study incorporated analyses of pH, total acidity, and ethanol content to obtain a comprehensive understanding of the wines’ chemical composition. Noteworthy, the study is expanding the sampling to consider more matrices within the winemaking process.

All of the aforementioned parameters, including the condensed tannin, were determined automatically using the BioSystems SPICA® analyzer. The technical simplicity of automated methods for phenolic evaluation, will lead to enhanced efficiency, robustness, and accuracy. Furthermore, these automated methods may facilitate greater field applications, leading to increased profitability and an opportunity to improve wine quality.