Occurrence of low molecular weight phenolics in Vitis vinifera red grape cultivars and their winemaking by-products from São Paulo (Brazil)

The content of low molecular weight phenolic compounds present in winemaking by-products (skins from grape marc and wine lees) of red wine made from the Vitis vinifera grape cultivars Cabernet Sauvignon and Cabernet Franc in the state of São Paulo (Brazil) has been examined. The study was extended to two consecutive years and showed that winemaking by-products still contained high concentrations of interesting functional and bioactive phenolic compounds. In addition to original grape phenolics, the winemaking by-products contained new phenolics originated by the action of enzymatic (yeast mediated) and chemical reactions during winemaking, including formation of anthocyanin-derived pigments and hydrolysis products from flavonol glycosides and tartaric esters of hydroxycinnamic acids. A total of 19 anthocyanins, 9 pyranoanthocyanins, 18 flavonols, 7 hydroxycinnamic acid derivatives, and 3 resveratrol-based stilbenes were identified. Wine lees have been revealed as an interesting source of flavonol aglycones and pyranoanthocyanins. The best sample preparation technique prior to the extraction of phenolic compounds, with regard to the maintenance of phenolic compound profiles and concentrations, was freeze-drying. However, in the case of lees, spray-drying showed to be also effective in the preservation of phenolic compounds and is a less expensive technique. Oven-drying at 50 °C should be avoided if there is interest in using winemaking by-products for further purposes, since phenolic compound concentrations were strongly reduced by thermal degradation.