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Oenological tannins are commercial natural products extracted from different botanical sources, which were widely reported as prominent contributors to wine quality. Research on wine quality affected by tannins extracts promoted the development of new oenological products with low cost and high accessibility. In the present study, the structure and concentration of tannin in polyphenol extracts, as well as their correlation with astringency and the color of model wine, was investigated by UV spectrophotometer, HPLC, fluorescence quenching, sodium dodecylsulfate-polyacrylamide gel electrophoresis, colorimeter and sensory evaluation.Resource extracts from 16 of 44 plants were screened as wine oenological tannins, according to the total polyphenol and total flavanol, as well as the intensity of astringency and bitterness. Polyphenols extracted from grape seeds and green tea were more effective in increasing the wine astringency compared to other plant tannins.Total flavanol content and tannin activity showed a strong correlation with wine astringency. Condensed tannins with mean degree of polymerization also exhibited strong color stability, and the concentrations of (-)-epigallocatechin were associated with the a* value, a negative qualitative factor for wine color. The present study provides new clues regarding the development of low-cost and highly accessible sources of polyphenol extracts and lays a theoretical foundation for the development of the oenological product. © 2022 Society of Chemical Industry.

Previous studies acknowledged that tartaric acid-imparted low-pH contributed to the enhancement of astringency, but in-depth studies are lacking and the underlying mechanisms are not clearly understood. This work introduced new insight into the effect of tartaric acid on astringency perception from the perspectives of complex formation, protein secondary structure, chemical bond type and salivary layer fluidity by establishing models using proteins (α-amylase, salivary proteins) and tannic acid. Results demonstrated that tartaric acid affects wine astringency by two mechanisms: a) Tartaric acid compound directly affects the wine astringency by forming ternary complexes and causing the protein structure to stretch by changing the hydrogen bond and hydrophobic bond between protein-polyphenol complexes. b) pH affected astringency by increasing the fluidity of the salivary layer rather than increasing the consumption of the salivary layer. The findings provide valuable information to the wine industry to regulate wine astringency by the management of tartaric acid.

The positive effect of mannoproteins (MPs) on wine astringency is of great interest during winemaking. Phenolic components with different structural characteristics in wine could elicit different intensities of astringency when combined with salivary proteins. Aiming to use commercial MPs to modulate the unbalanced wine astringency, this work selected three commercial MPs and phenolic fractions (phenolic acids, monomeric/oligomeric procyanidins, polymeric procyanidins) with different mDP extracted from wine. The relationship between the structure and concentration of MPs, phenolic fractions, and astringency was investigated by physicochemical techniques (fluorescence quenching, SDS-PAGE, dynamic light scattering, and isothermal titration calorimetry) and sensory evaluation. Results showed that 0.6 g/L of MPs played a role in reducing wine astringency. MPs were more effective in inhibiting the interaction between monomeric/oligomeric or polymeric procyanidins and proteins than that of phenolic acids, through ternary or competitive mechanisms. Moreover, MPs with high protein portion and high molecular weight exhibited a stronger binding capacity to phenolics or protein, thus showing competing effect with phenolics for binding to protein. This work could provide the wine industry with valuable information for optimizing the application of commercial MPs to modulate wine astringency.