α-Glucosidase Inhibitory Activity and Total Flavonoid Content of Green and Purple Kale (Brassica oleracea L.) Leaf Extracts

Wempi Budiana (Biological Pharmacy Research Group, Faculty of Pharmacy, Universitas Bhakti Kencana, Bandung 40617, West Java, Indonesia)
Dewi Kurnia (Biological Pharmacy Research Group, Faculty of Pharmacy, Universitas Bhakti Kencana, Bandung 40617, West Java, Indonesia)
Ina Rodinah (Bachelor of Pharmacy Study Program, Faculty of Pharmacy, Universitas Bhakti Kencana, Bandung 40617, West Java, Indonesia)

Indonesian Journal of Jamu
Vol. 11 No. 5 (2026): Jurnal Jamu Indonesia (In Progress)

Type 2 diabetes mellitus is managed in part by delaying carbohydrate digestion through α-glucosidase inhibition. Kale (Brassica oleracea L.) is rich in flavonoids, but green and purple kale have not been compared under identical extraction conditions. Leaves of both varieties were extracted sequentially by reflux with n-hexane, ethyl acetate, and 96% ethanol. α-Glucosidase inhibition was assayed in vitro with p-nitrophenyl-α-D-glucopyranoside, and total flavonoid content by the aluminum chloride method. IC50 values, in that solvent order, were 82.70, 59.87, and 77.32 µg/mL for green kale and 78.35, 52.25, and 76.80 µg/mL for purple kale, against 74.63 µg/mL for acarbose. Flavonoid content followed the same pattern: 24.61–32.71 mg QE/g extract in green kale and 26.02–35.97 mg QE/g extract in purple kale. The ethyl acetate extract of purple kale was the most active and the most flavonoid-rich, indicating that semi-polar constituents drive α-glucosidase inhibition by kale leaves.