Identification of novel bioactive proanthocyanidins with potent antioxidant and anti-proliferative activities from kiwifruit leaves

Agro-wastes contribute major social, economic, and environmental challenges for food production and circular economy systems. The current increasing demand for clean label food production and use of natural bioactive compounds could turn these challenges into opportunities providing avenues for proper utilization of agro-wastes to produce valuable products. This study aimed to investigate the potential use of kiwifruit (Actinidia chinensis) leaves as a source of proanthocyanidins (PAs) bioactive phenolic phytochemicals. Kiwifruit leaves PAs were extracted, purified, identified, and evaluated for their antioxidant and anti-proliferative activities. The structural composition of the purified PAs was characterized using HPLC-QTOF-MS/MS and MALDI-TOF-MS. The results showed that purified kiwifruit leaves PAs (PKLPs) comprised mainly procyanidins, propelargonidins, and prodelphindins ranging from dimers to hexamers with (epi)catechin as terminal units and (epi)afzelechin or (epi)gallocatechin as dominant extension units. This study reports the structure of novel PKLPs monomer fractions was unique compared to the PAs that extracted from the other plant sources. The PKLPs exhibited higher phenolic content than the skin and flesh of several kiwifruit cultivars. Moreover, the PKLPs exhibited higher in vitro antioxidant activity in chemical-based (DPPH, ABTS, and FRAP) assays and H2O2-induced injury cell model than ascorbic, Trolox, and catechin (p < 0.01). A remarkable dose-dependent anti-proliferation activity (IC50 = 186.04 ± 2.61 μg/mL) against HepG2 cells was observed. In conclusion, this study demonstrated that kiwifruit leaves waste could serve as a sustainable and low-cost source of PAs, a group of multi-functional bioactive compounds that plays a key role in the food and pharmaceutical industries.