Researchers at the Federal University of Technology in Nigeria evaluated the effects of the aqueous extract of garlic, white onion and purple onion on the activity of angiotensin-converting enzyme (ACE), a-amylase and a-glucosidase in vitro. They reported their findings in an article published in the Journal of Dietary Supplements.

• Spices are used in cooking and serve as ingredients in several traditional delicacies that contain natural antioxidants, such as polyphenols.
• To assess the beneficial properties of garlic, white onion and purple onion extracts, the researchers investigated their effects on the activity of various enzymes.
• They also determined the extracts’ antioxidant capacities using OH*, Fe2+ chelation, and 2, 2?-azino-bis 3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical-scavenging assays.
• The researchers found that the garlic, purple onion and white onion extracts inhibited the activities of ACE, a-amylase and a-glucosidase in a concentration-dependent manner.
• The purple onion extract (IC50 = 0.59 mg/ml) had a higher inhibitory effect on ACE than the white onion (IC50 = 0.66 mg/ml) and garlic (IC50 = 0.96 mg/ml) extracts.
• White onion (IC50 = 3.93 mg/mL), on the other hand, had a significantly stronger inhibitory effect on a-amylase than garlic (IC50 = 8.19 mg/ml) and purple onion (IC50 = 8.27 mg/ml).
• Garlic (IC50 = 4.50 mg/ml) showed a similar inhibitory effect on ?-glucosidase activity to white onion and purple onion.
• All three extracts were able to scavenge DPPH and reduce Fe3+ to Fe2+ in the antioxidant assays in a dose-dependent manner.

Based on these findings, the researchers concluded that garlic, white onion and purple onion exert anti-diabetes and antihypertensive properties by inhibiting ACE, a-amylase and a-glucosidase activity and preventing lipid peroxidation in the pancreas and heart through their antioxidant activities.

Journal Reference:

Oboh, G, Ademiluyi AO, Agunloye OM, Ademosun AO, Ogunsakin BG. INHIBITORY EFFECT OF GARLIC, PURPLE ONION, AND WHITE ONION ON KEY ENZYMES LINKED WITH TYPE 2 DIABETES AND HYPERTENSION. Journal of Dietary Supplements. 09 March 2018;16(1):105-118. DOI: 10.1080/19390211.2018.1438553