Phenolamide-driven α-glucosidase inhibitory activity in immature fruits of the korean landrace-derived chili pepper Sumihyang

Understanding the biochemical basis of α-glucosidase inhibitory (AGI) activity in chili peppers (Capsicum annuum L.) is essential for their development as functional food ingredients. This study evaluated AGI activity and phytochemical profiles across four ripening stages in three C. annuum cultivars: Sumihyang (a cultivar derived from the Korean landrace Subicho), Dangjo (a functional antidiabetic cultivar), and Olbokhap (a disease-resistant commercial cultivar). Enzyme assays revealed that AGI activity peaked at the immature stage in all cultivars, with Sumihyang consistently exhibiting the highest activity across two harvest periods. Untargeted metabolomic profiling at the immature and turning stages identified two phenolamides, caffeoylputrescine and feruloylputrescine, that were selectively enriched in immature Sumihyang and strongly correlated with AGI activity (r > 0.92). While the AGI effect of caffeoylputrescine has been previously reported, feruloylputrescine was evaluated here for the first time under this assay system. In vitro validation confirmed their inhibitory activities, with half maximal inhibitory concentration (IC₅₀) values of 193 μM for caffeoylputrescine and 291 μM for feruloylputrescine. These findings suggest that phenolamide composition, rather than total flavonoid content, is a key determinant of AGI activity in chili peppers. The selective accumulation of these phenolamides in immature Sumihyang highlights its potential as a genetic resource for developing antidiabetic functional foods.