A comparative study on antihypertensive and antioxidant properties of phenolic extracts from fruit and leaf of some guava (Psidium guajava L.) varieties

Investigation of antihypertensive and antioxidant properties of fruit and leaf extracts from four varieties (giant white, small white, stripped and pink) of guava (Psidium guajava L.) in vitro was the focus of this study. Consequently, methanol/1 M HCl (20:1 v/v) extraction of fruit and leaf of the guava varieties were carried out. Thereafter, the extracts were assayed for their angiotensin I converting enzyme (ACE) inhibitory effect, total phenol and flavonoid contents, reducing property, radicals (DPPH, ABTS^•+, hydroxyl and nitric oxide) scavenging ability, Fe²⁺ chelating ability, and inhibition of Fe²⁺ and Sodium nitroprusside (SNP) induced lipid peroxidation reactions (in vitro). Furthermore, the phenolic constituents of the extracts were characterised with gas chromatography (GC). The results showed that all the extracts significantly (P < 0.05) inhibited ACE activity, scavenged (DPPH, ABTS^•+, nitric oxide and hydroxyl) radicals, chelated Fe²⁺ and also inhibited Fe²⁺ and SNP induced lipid peroxidation in rat heart (in vitro). Nevertheless, the pink guava variety had the highest ACE inhibitory and antioxidant properties. In addition, Rosmarinic acid, eugenol, carvacrol, catechin and caffeic acid were the dominant phenolics found in the extracts. The ACE inhibitory effects and antioxidant properties of the guava extracts, which correlates significantly with their phenolic constituents, could largely contribute to their antihypertensive properties as obtained in traditional medicine.