Effect of solvent types and extraction times on phenolic and flavonoid contents and antioxidant activity in leaf extracts of Amomum chinense C

The present study determined the phenolic and flavonoid contents in Amomum chinense C. leaf extracts obtained using four extracting solvents(distilled water, 80% methanol, 80% ethanol and 80% acetone)with various extraction times (6h, 12h and 24h) at 37oC. All extraction conditions significantly (p <0.05) affected the phenolic contents and antioxidant activity of the leaf extracts. The optimal conditions used for extracting the phenolic compounds from A. chinense leaves were 80% methanol for 12h, which provided a higher amount of phenolics and antioxidant activity compared to the other conditions tested. There was a strong correlation between total phenolic content and antioxidant activities based on the three assays with correlation coefficients of 0.805, 0.873 and 0.975 for DPPH, ABTS and FRAP assays, respectively. HPLC analyses of all extracts revealed that the major phenolic acids identified in the tested extracts were chlorogenic acid, cinnamic acid, ferulic acid and caffeic acid, whereas catechin, rutin and quercetin were the major of flavonoids.