Unveiling flavonoids in Alpinia species indigenous to Thailand and their relevance with radical scavenging potential and α-glucosidase inhibitory activities

The rhizomes of plants in the genus Alpinia (Zingiberaceae) have been used as food, spices, and traditional medicine in Thailand. The crude ethanolic extracts from the fresh rhizomes of selected Alpinia species, including A. galanga var. galanga, A. galanga var. pyramidata, A. oxymitra, and A. siamensis, were proposed to be explored for their active principles and in vitro antioxidant and antidiabetic performance. The fresh rhizomes were extracted with 95% ethanol using a Soxhlet apparatus, and crude extracts were subsequently analyzed for amounts of flavonoids using quercetin and kaempferol as chemical markers by high-performance liquid chromatography. All flavonoid-containing extracts were evaluated for their antioxidant and antidiabetic effects using free radical scavenging and alpha-glucosidase inhibitory tests. The results demonstrated that the examined extracts included active flavonoid markers, predominantly quercetin, which ranged from 11.05% to 13.79% w/w and was approximately 10 times more prevalent than kaempferol. Extracts that consisted of these active flavonoids exhibited strong antioxidant and alpha-glucosidase inhibitory activities. Pearson's correlation study was used to determine the association between flavonoid quantity and possessed activities. The findings indicated a substantial correlation between quercetin levels and free radical scavenging activity. This work implies that raw ethanolic extracts from the fresh rhizomes of these rare Alpinia plants have the potential to be developed into functional nourishment and remedies that could benefit diabetics in alternative ways.