INHIBITION OF α - AMYLASE, α-GLUCOSIDASE AND ANGIOTENSIN -1 CONVERTING ENZYME ACTIVITIES BY AQUEOUS EXTRACTS OF SOME ALLIUM SPECIES

Abstract

With the cure for type-2 diabetes and hypertension still elusive, the inhibition of key enzymes linked to these diseases, as management strategy, using natural sources cannot be over-emphasized. Hence, this study sought to investigate the effect of aqueous extracts of some Allium species (Garlic, pink onion and white onion) on key enzymes linked to type 2 diabetes (α-amylase and α-glucosidase) and hypertension (Angiotensin I converting enzyme ACE), antioxidant properties and to characterize the phenolic and allicin constituents of the Allium spp. The result revealed that extracts of all the Allium spp α-amylase and α-glucosidase (0 – 4 mg/ml) as well as ACE (0 – 1.4 mg/ml),. in a dose dependent manner. However, the IC5O values ranged between 3.93 (white onion) – 8.27 mg/ml (pink onion) for α-amylase activities, 4.11 (Garlic) - 4.50 mg/ml (pink onion) for α-glucosidase and 0.59 (pink onion) – 0.96 mg/ml (white onion) for ACE activities. Garlic had the highest total phenol (6.6g mg GAE/g) and flavonoid (0.43 mg/ml) contents while white onion had the least total phenol (4.21 mg GAE/g) and flavonoids (0.07 mg QUE/g) content. The study also revealed that all Allium spp exhibited strong antioxidant properties and rich in constituent phenolic compounds. The GC-FID analysis revealed the presence of Diallyl; methyl allyl – and Ally methyl – thiosulphinate as the major allicin constituents of the Allium species. Furthermore, P-coumaric acid. p-hydroxybenzoic acid, caffeic acid, ferulic acid and sinapinic acid are the dominant phenolics in garlic, protocatechuic acid, vanillic acid, p-hydrozybenzoic acid, ferulic and phloroglucinol are the dominant phenolics in pink onion and protocatenhnic acid, vanillic acid, p-hydroxybenzoic acid, ferulic acid and sinapinic acid are the dominant phenolics in white onion. Consequently, the α-amylase and α-glucosidase and ACE inhibitory activities of the Allium spp suggest their antidiabetic and antihypertensive properties. These therapeutic properties may be attributed to their allicin and phenolic constituents. However, white onion exhibited the strongest antihypertensive property