Comparison of (poly)phenolic compounds and antioxidant properties of pomace extracts from kiwi and grape juice

The aim of this study was to evaluate the phenolic profile of grape and kiwi juice pomace by HPLC-ESI-MS, and their correlation with antioxidant properties determined with DPPH, FRAP and OH scavenging assays. A total of 32 compounds have been identified including anthocyanins, flavonols, flavan-3-ols and phenolic acids. Significantly higher relative amounts of anthocyanin monoglucosides, flavan-3-ols (catechin, epicatechin, and procyanidin), and flavonols (quercetin and its derivatives) were found for grape pomace. Whereas kiwi pomace contained higher amounts of quinic acid, caffeic acid and its derivatives. Although grape pomace had higher total phenolic content (TPC), it showed lower OH scavenging capacity than kiwi pomace, but better DPPH scavenging activity and reducing power. This indicated that the antioxidant activities do not only rely on the TPC but also associate with their phenolic profiles. Overall the two pomaces could potentially be exploited as an inexpensive source of natural antioxidants for food production.