Cluster Sun Exposure and Quercetin in Pinot noir Grapes and Wine

Abstract

Anthocyanin and flavonol content of disks of sun-exposed Pinot noir (Vitis vinifera L.) berry skin were compared to disks from shaded berries from the same clusters. Anthocyanin content was not affected by sun exposure, but quercetin glycoside concentration of sun-exposed disks was 1.46 µg mm^-2 for the sun-exposed disks compared to 0.14 µg mm^-2 for the shaded. Wines were made from Pinot noir clusters from a single vineyard block from three different sun exposure levels: shaded, moderately exposed and highly exposed. The concentration of quercetin glycosides in wine was 4.5, 14.8, and 33.7 mg L^-1 in the shaded, moderate and highly exposed treatments, respectively. The level of quercetin aglycone also increased with sun exposure. Cluster sun exposure appears to be the primary factor determining quercetin levels in grapes and wine. Wines from highly and moderately exposed cluster positions had higher total anthocyanin levels than those from shaded clusters, but wines from highly exposed clusters had 40% greater polymeric anthocyanins than the other two treatments. Caftaric acid, catechin, and epicatechin concentrations in wine were inversely related to cluster sun exposure. The low levels of caftaric acid in wines from sun-exposed clusters appeared to be related to hydrolysis of the tartaric ester, with wines from highly sun-exposed clusters having 50% more caffeic acid than moderate and 130% more than shaded clusters. Caffeic acid was not present in fruit samples. It is possible that the increase in polymeric anthocyanins in wines from sun-exposed clusters is directly related to quercetin levels. High wine quercetin levels may increase the rate of polymerization with potential stability and quality implications.