Phenolic Extracts From Grapefruit Peels (Citrus Paradisi) Inhibit Key Enzymes Linked With Type 2 Diabetes and Hypertension

This study sought to characterize the interaction of phenolic extract from grapefruit peels with α-amylase, α-glucosidase and angiotensin-I-converting enzyme (ACE) activities. The free phenolic of grapefruit peels was extracted with 80% acetone, while the bound phenolic was extracted from the alkaline and acid-hydrolyzed residue with ethyl acetate; and their interaction with the enzymes were assessed. The phenolic extracts inhibited α-amylase, α-glucosidase and ACE enzyme activities; however, free phenolic had significantly higher (P < 0.05) α-amylase and α-glucosidase inhibitory activities than bound phenolic, while there was no significant difference (P > 0.05) in their ACE inhibitory activities. Nevertheless, the extracts were strong inhibitor of α-glucosidase when compared to α-amylase. The phenolic inhibited sodium nitroprusside-induced lipid peroxidation in pancreas in a dose-dependent manner. Therefore, free and bound phenolic extracts from grapefruit peels could be used as nutraceutical for the management of hypertension and type 2 diabetes. PRACTICAL APPLICATIONS Type 2 diabetes (including its precursor, metabolic syndrome) is one of the top five most significant diseases in the developed world and is rapidly becoming a burden in sub-Sahara Africa. Natural inhibitors with relatively mild inhibition of α-amylase but strong inhibitor of α-glucosidase activity could be an effective therapy for type 2 diabetes with minimal side effects, while the inhibition of angiotenisn-I-converting enzyme is a useful approach in the treatment of hypertension in both diabetic and nondiabetic patients, and phenolics have promising potential. Our findings in this study have shown that grapefruit peels that are usually considered to be waste could be a cheap and good source of free soluble and bound phenolics with antidiabetic and antihypertensive potentials.