Effect of thermomaceration and enzymatic maceration on phenolic compounds of grape must enriched by grape pomace, vine leaves and canes

Grape pomace, leaves and canes generated by the wine industry are excellent and valuable resources to recover polyphenolic compounds with strong antioxidant capacity. Hence, the main objective of this work was to study the extraction process and the quality of grape juices enriched in the phenolic compounds extracted from grape skins, seeds and flesh, autumn leaves and canes of the Vitis vinifera species, cvs. País and Lachryma Christi. Thermomaceration of a mixture of grape must and pomace (8:1 w/w) at 60 °C resulted in a higher extraction degree of polyphenols, compared to maceration with pectolytic enzymes commonly used in enology. However, extraction modified pH and acidity of grape musts affecting anthocyanin contents of the samples. Generally, musts enriched by vine leaves and grape pomace of the Lachryma Christi cultivar showed the highest antioxidant properties, where must mashed on skins with seeds resulted into maximum total polyphenol contents of 2855 mg/L of gallic acid equivalents and must in contact with leaves yielded maximum antioxidant capacity of 93.5 mmol/L of Trolox equivalents. The juices using grape pomace were rich in anthocyanins (malvidin-3-glucoside) and flavan-3-ols (catechin and epicatechin); flavonols (quercetin-3-glucoside) and phenolic acids (caftaric and coutaric acid) were the main compounds in leaf extracts. Thermomaceration using grape pomace and vine leaves is preferred in order to achieve a grape must with a high amount of polyphenolics and antioxidants.