Comparative analysis of phenolic compounds in different thinned unripe kiwifruits and their biological functions

Thinned unripe kiwifruits (TUK) are considered the major agro by-products in kiwifruit production. To promote their potential applications, polyphenols and biological effects of unripe fruits from nine commercial kiwifruit cultivars were compared. Our findings showed that TUK were rich in bioactive polyphenols, which varied greatly by different cultivars. Indeed, catechin, epicatechin, procyanidin PB1, procyanidin B2, protocatechuic acid, neochlorogenic acid, and gallic acid were measured as the major phenolic components in most TUK, with the highest levels observed in ‘Hongao’ and ‘Cuiyu’ cultivars. Furthermore, TUK exerted strong in vitro antioxidant capacities, inhibitory effects on digestive enzymes, and anti-inflammatory activities. Particularly, their stronger antioxidant effects and inhibitory effects on digestive enzymes were probably attributed to their higher contents of phenolic compounds, especially procyanidin B2. Collectively, our findings reveal that TUK are potential resources of valuable polyphenols, which can be exploited as natural antioxidants and natural inhibitors of α-glucosidase and α-amylase.