The effects of different protein:tannin ratios on the tartrate-holding capacity of wine model solutions

Research progress of tartaric acid stabilization on wine characteristics

Tartaric acid is one of the characteristic acids in wine, playing a crucial role in wine characteristics. However, superabundant tartaric acid will form insoluble salts and precipitate in the form of crystals, affecting consumers' purchasing appetite. Therefore, tartaric stability is also one of the important indices for controlling the wine quality. At present, the main processing methods for tartaric stability include cold stabilization, ion exchange treatment, electrodialysis and the addition of exogenous components (gum arabic, metatartaric acid, carboxymethyl cellulose, mannoprotein and potassium polyaspartate). This review summarizes and analyzes the origin of tartaric acid in wine, factors influencing the tartaric stability, detection methods, treatments for tartaric stabilization, and the effects of these methods on the sensory quality of wine. Comparing the effects of these methods on wine quality can provide a basis for the further study of tartaric stabilization methods in order to select an appropriate tartaric stabilization method.

Antioxidant activity of commercial food grade tannins exemplified in a wine model

Although commercial tannins are widely used in foods and beverages, an improved understanding of the structure and composition of vegetable tannins is needed to promote the exploitation of agri-food by-products and waste and their valorisation in more sustainable industrial applications. This study aims to characterise the phytochemical composition and antioxidant activity of 13 food grade tannins using multiple analytical approaches, including spectrophotometry and HPLC-ECD to determine the amount of targeted polyphenolic compounds. Moreover, the antioxidant activity of tannins was assessed in terms of radical scavenging activity (DPPH• assay), reducing power (FRAP assay), and redox properties (cyclic voltammetry, CV). A statistical univariate and multivariate correlation analysis was performed on 17 parameters including tannin content (range: 0.71-1.62 mM), gallic acid, (+)-catechin, syringic acid and (‒)-epicatechin. The compositional profile of tannins was related to their chemical moiety, antioxidant activity and the botanical origin of the extracts. In particular, the CV signal at 500 mV was highly correlated with DPPH• value due to the catechol ring of flavonoids and trigalloyl moieties of gallic acid-based compounds. Practical examples of tannins application in winemaking are discussed.

Pathogenesis-Related Proteins Limit the Retention of Condensed Tannin Additions to Red Wines

Exogenous additions of condensed tannin (CT) to must or wine are a common winemaking practice, but many studies have reported inexplicably low and variable retention of added CT. We observed that additions of purified CT to red wines can result in the formation of an insoluble precipitate with high nitrogen content. Proteomic analysis of the precipitant identified several classes of pathogenesis-related proteins. Proteins in juices and red wines were quantitated by SDS-PAGE and were highest in native Vitis spp., followed by interspecific hybrids and Vitis vinifera. Wine protein was positively correlated with the ratio of juice protein to the quantity of tannin derived from fruit. The binding of added CT by wine protein could be well modeled by the Freundlich equation. These observations may explain the poor CT retention in previous studies, particularly for interspecific hybrids, and also indicate that protein removal during winemaking may improve exogenous CT retention.