Comparative functional analysis of papaya leaves at different developmental stages

Papaya (Carica papaya L.), a tropical plant belonging to the Caricaceae family, is widely cultivated in tropical and subtropical countries. Young leaves grow from the stem tips, petioles elongate, and leaf color changes from light green to dark green during development. Papaya leaves are used as therapeutic agents in folk medicine and potential functional food materials; however, the specific associations between the leaf development stage and functional components of papaya remain unknown. Therefore, in this study, we aimed to conduct a non-targeted analysis of the four developmental stages of papaya leaves via liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry. Specifically, we focused on carpaine derivatives and γ-aminobutyric acid that have attracted attention in the Japanese functional food industry. Carpaine derivatives were abundant in young leaves; however, their levels decreased with increasing leaf maturity. In contrast, γ-aminobutyric acid levels increased with increasing leaf maturity. Multivariate analyses revealed that the metabolites changed more significantly during the transition to the dark green phase than during the transition from the early yellow green to bright green phase. Additionally, proteolytic activity was evaluated using casein as a substrate. Proteolytic activity decreased with increasing leaf maturity. In conclusion, our findings suggest that leaves at different developmental stages should be selected based on their functional components and intended application.