Yiliang Cheng and Aude Watrelot*
*Iowa State University, 2567 Food Science Building, 536 Farm House Ln, AMES, IA, 50011 (watrelot@iastate.edu)

To overcome the challenge of low tannin concentration in red wines made from cold-hardy hybrid grapes (Vitis spp.), we previously applied both the accentuated cut edges (ACE) technique and maceration enzymes to Marquette grapes (Vitis spp.) at crushing. A higher tannin concentration was found in treated wines and was associated with the degradation of cell wall polysaccharides. However, the concentration of tannin diminished up to 45% between the third day of alcoholic fermentation and after pressing, regardless of treatment. To improve tannin retention, a better understanding of adsorption and interaction mechanisms between tannin and grape macromolecules is necessary. We examined the impact of grape flesh on retention of tannins from Pinot noir and Marquette skins and seeds under a wine-like condition. After peeling, each grape tissue (skin with/without flesh; seed with/without flesh; and a combination of skin, seed, and flesh) was soaked in a wine-like solution for five days. After soaking, tannin and anthocyanin concentrations in supernatants were quantified by HPLC-DAD/FLD. The composition of tannin was analyzed by HPLC-DAD after acid catalysis in the presence of an excess of phloroglucinol. In both cultivars, flesh caused a large decrease of tannin concentration in the supernatant of seed condition, followed by skin condition, and led to a decrease of monomeric anthocyanin concentrations. A lower mean degree of polymerization of tannins in supernatants of the Pinot noir skin, seed, and flesh combination compared to skin only suggested that larger tannins bind to macromolecules from the flesh. These results indicated that degradation of flesh tissues (for example, combining protease and pectinase) might be a potential strategy to hinder adsorption of extracted tannin further and improve retention of tannins in the finished wine.

Funding Support: No funding source.