Effect of Different Drying Methods and Solvents on Phenol Content, Antioxidant and Antihyperglycemic Activity of Ginger Rhizome Extract (Alpinia mutica Roxb.)

Abstract

Alpinia mutica Roxb. (Zingiberaceae), also known as halia hutan is a plant rich in various bioactive compounds (i.e. α-terpineol, linalool and camphor) that are reported to be capable of fighting cancer cells and has the potential to act as a natural antioxidant. This study was carried out to investigate the effect of different drying methods (oven drying (OD) and freeze-drying (FD)) and different extraction solvent ratio of ethanol:water (100:0, 50:50 and 0:100) on the phenolic content, antioxidant and antihyperglycemic activity of A. mutica rhizome extract (ERA). The phenolic content of ERA was determined using Total Phenolic Content (TPC) while antioxidant activity was measured using DPPH (2,2-diphenyl-1-picrylhydrazyl) Free Radical Scavenging test and Ferric Reducing Antioxidant Power (FRAP) test. Antihyperglycemic activity was determined by measuring the inhibition of α-glucosidase enzyme activity. Using the Pearson Correlation test, the correlation between phenolic content and antioxidant and antihyperglycemic activity was evaluated. The findings of this study indicated that the different drying methods and types of solvent may have significant effects on the phenolic contents, antioxidant and antihyperglycemic activity of ERA. Sample OD extracted with 100:0 showed the best antioxidant (DPPH) and antihyperglycemic activity with the lowest IC50 value of 550.94 ± 50.02 and 84.97 ± 11.69 µg/mL. PK (100:0) also showed highest phenolic content (155.55 ± 9.36 mg GAE/g extract) and FRAP value (108.98 ± 10.08 mg TEAC/g extract) significantly (p < 0.05) compared to other samples. A positive correlation between TPC with antioxidant and antihyperglycemic activity showed that the phenolic compound may be responsible for the biological activity obtained. This finding suggested that the total phenolic content, antioxidant and antihyperglycemic effects of ERA is significantly influenced by drying technique and extraction solvents used.