Inhibitory effect of polyphenol-rich extracts of jute leaf (Corchorus olitorius) on key enzyme linked to type 2 diabetes (α-amylase and α-glucosidase) and hypertension (angiotensin I converting) in vitro

Corchorus olitorius leaf is consumed in various parts of the world as leafy vegetable and folk remedy for the management of some degenerative diseases with dearth of information on its biochemical rationale. Therefore, this study sought to characterize the inhibitory action of polyphenol-rich extracts (free and bound) of C. olitorius on alpha-amylase, alpha-glucosidase and angiotensin I converting enzyme (ACE), as well as to identify the phenolic compound responsible for these activities. Our findings revealed that the extracts inhibited alpha-amylase and alpha-glucosidase (12.5-50.0 mu g/mL), and ACE (10.0-50.0 mu g/mL) in dose-dependently with free extracts having significantly (P < 0.05) higher a-amylase (17.5 mu g/mL), alpha-glucosidase (11.4 mu g/mL) and ACE (15.7 mu g/mL) inhibitory activities as revealed by the IC50. Reversed-phase HPLC analysis of the extracts revealed chlorogenic acid (7.5 mg/100 g) and isorhamnetin (51.1 mg/100 g) as the main phenolics in the free extract and caffeic acid (58.1 mg/100 g) in the bound extract. Therefore, the enzyme inhibitory activity of C. olitorius extracts may be attributed to the presence of caffeic acid, chlorogenic acid and isorhamnetin, thus justifying its use in folklore for the management of diabetes and hypertension. (C) 2012 Elsevier Ltd. All rights reserved.