Abstract

This study highlighted the proximate composition, metabolites, and in vitro biological activities of three papaya leaf cultivars in Thailand: Khaek Dam (K), Holland (H), and Thai Local (L), according to leaf age (young, middle, and old). The young-aged leaves of three cultivars showed significantly more protein and fiber content, as well as total phenolic content (TPC), total flavonoid content (TFC), and tannin content (TC) than the middle-aged and old-aged leaves (p<0.05). Furthermore, the metabolite profiles of young leaves from three cultivars exhibited the highest concentrations of phenolic compounds. Other metabolites, including alkaloids, terpenoids, indoles, amino acids, saccharides, lipids, and vitamins, increased in middle-aged leaves. The K cultivar outperformed the H and L cultivars in terms of TPC, TFC, and antioxidant activity at all leaf maturities. The young and middle-aged leaf extracts from all three cultivars revealed the highest DPPH radical scavenging activity (p<0.05). The middle-aged leaves of the three extracts had the lowest IC<inf>50</inf> for inhibiting α-amylase and α-glucosidase, resulting in excellent glycemic control. The extracts from middle-aged and young K leaves were non-toxic to RAW 264.7 murine macrophage cell line and significantly reduced NO production at doses ranging from 0.98 to 62.5 µg/mL. K-young and middle-aged leaf extracts demonstrated high antioxidant activity. As a result, K-young and middle-aged leaf extracts are highly desirable as functional food additives.