Evaluation of antioxidant and α-glucosidase inhibitory activity of green tea powder from Indonesian tea cultivars

The enzyme α-glucosidase plays a crucial role in the digestive system by hydrolyzing carbohydrates to produce absorbable glucose. With the recent surge in the popularity of green tea powder (GTP) in Indonesia, this study aims to determine the potential of GTP derived from Indonesian tea cultivars as sources of antioxidants and inhibitors of α-glucosidase activity. Four Indonesian tea cultivars ('GMB-3', 'GMB-7', 'GMB-9', and 'GMBS-4') were utilized to produce green tea powder, following which their physicochemical properties, antioxidant activity, and α-glucosidase inhibition activity were evaluated. The results revealed that GTP has particle size at d₅₀ ranging from 1.03 to 1.96 μm with total polyphenol content of GTP ranging from 244.57 to 277.91 mg GAE/g. Notably, the 'GMBS-4' cultivar produced GTP with the highest total flavonoid content (223.52 mg QE/g), the lowest IC₅₀ (12.27 mg/L), and exhibited the highest α-glucosidase inhibitory activity (42.54%). Furthermore, the GTP derived from the 'GMB-3' cultivar exhibited a higher total catechin content (4.39%) compared to the other cultivars. The inhibition of α-glucosidase activity of GTP ranged from 30% to 42% at a concentration of 500 μg/mL. These findings suggest that Indonesian green tea powder exhibits α-glucosidase inhibitor activity, although at a concentration higher than acarbose. However, Indonesian tea cultivars demonstrate promising potential for producing green tea powder with antioxidant properties and α-glucosidase inhibitors. Therefore, further research and development of Indonesian tea cultivars are expected to improve GTP quality in Indonesia.