Inhibitory Effects of Onion Against α-Glucosidase Activity and its Correlation with Phenolic Antioxidants

Onion is used for treating diabetes in Chinese civil practices; however, the anti-diabetic mechanism was not clear. To investigate the potential mechanism of onion in diabetes treatment, total phenolic content, antioxidant activity, and α-glucosidase and α-amylase inhibitory activity were assessed. Both 70% ethanol extracts and boiling water extracts from white onion, red onion, and commercial dry onion powder, bitter melon, pumpkin, yam, and medlar exhibited inhibitory activities against α-glucosidase. Total phenolic content values of samples were positively related to α-glucosidase inhibitory activities (p < 0.05). Antioxidant analyses suggested that onions possessed strong free radical scavenging capacities. These results indicated that onions showed potential to be effective anti-diabetic agents.