Analysis of Multidimensional Characterization Methods for Tannin Quality in Dry Red Wine

Tannins are important polyphenolic compounds that significantly influence the sensory characteristics of color, aroma, and taste in dry red wine. This study compared various methods for tannin analysis, including spectroscopic quantification, total phenols, monomers, binding characteristics, and astringency quality, so as to provide the methodological support for the comprehensive characterization of tannin quality in dry red wine.

The study used 18 Xinjiang dry red wines aged from 1 to 9 years. Tannin spectroscopic quantification was conducted using the Folin-Denis method, Bate-Smith method, hydrochloric acid-vanillin method, protein precipitation method, and methyl cellulose method. Total phenols were measured using the Folin-Ciocalteu reagent method, while flavanols and flavonols were quantified using UV-visible spectrophotometry. Aggregation characteristics were analyzed using the hydrochloric acid, ethanol, and gelatin precipitation methods. Tannin astringency quality was evaluated by a trained sensory panel, assessing six attributes: astringency balance, astringency intensity, acidity intensity, dryness, puckery, and smoothness.

In comparison to other spectroscopic quantification methods, the methyl cellulose method showed higher recovery rate, with the recovery rates of mixed tannins added to simulated wine, raw wine, and finished wine being 130.67%, 107.54%, and 76.94%, respectively. Tannin content, as measured by the five spectroscopic methods, decreased with wine age, with the methyl cellulose method (1 247-3 103 mg·L^-1) and the Bate-Smith method (1 643-5 064 mg·L^-1) showing distinct trends. Total phenol (3 145-4 383 mg·L^-1), flavanols (352-1 151 mg·L^-1), and flavonols (107-199 mg·L^-1) content also decreased as wine age increased, with correlation coefficients of 0.71, 0.65, and 0.29 with the methyl cellulose method, respectively. The hydrochloric acid index (0.11-0.35) and ethanol index (0.21-0.44) showed an increasing trend with wine age, while the gelatin index (0.08-0.53) showed no clear trend. Sensory analysis revealed that astringency intensity was most prominent in the 1-3 year group, gradually weakening as the wine aged, with a reduction in puckery and an increase in smoothness. Principal component analysis (PCA) of the tested samples indicated that spectroscopic quantification, flavanol content, astringency intensity, and puckery were the most important factors in most to differentiating between wine samples. Wines in the 1-3 year group had higher tannin content and stronger astringency; wines in the 4-6 year group had weaker astringency but the strongest acidity and dryness; wines in the 7-9 year group had higher tannin polymerization and the weakest astringency but stronger acidity.

The methyl cellulose method has been shown to be the most effective for determining total tannin content in dry red wines. Total phenols and flavanols were effective at quantifying both the overall and monomeric tannin characteristics. The hydrochloric acid index and ethanol index were effective indicators of tannin binding characteristics, while astringency intensity and puckery were key indicators for distinguishing the sensory attributes of tannins.