Evaluation of hydroxyl radical-scavenging property of garlic.

Garlic has been reported to provide protection against hypercholesterolemic atherosclerosis and ischemia-reperfusion-induced arrhythmias and infarction. Oxygen free radicals (OFRs) have been implicated as causative factors in these diseases and antioxidants have been shown to be effective against these conditions. The effectiveness of garlic in these disease states could be due to its ability to scavenge OFRs. However, the OFR-scavenging activity of garlic is not known. Also it is not known if its activity is affected by cooking. We therefore investigated, using high pressure liquid chromatography, the ability of garlic extract (heated or unheated) to scavenge exogenously generated hydroxyl radical (.OH). .OH was generated by photolysis of H2O2 (1.2-10 mumoles/ml) with ultraviolet (UV) light and was trapped with salicylic acid (500 nmoles/ml). H2O2 produced .OH in a concentration-dependent manner as estimated by .OH adduct products 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA. Garlic extract (5-100 microliters/ml) produced an inhibition (30-100%) of 2,3-DHBA and 2,5-DHBA generated by photolysis of H2O2 (5.00 pmoles/ml) in a concentration-dependent manner. Its activity is reduced by 10% approximately when heated to 100 degrees C for 20, 40 or 60 min. The extent of reduction in activity was similar for the three heating periods. Garlic extract prevented the .OH-induced formation of malondialdehyde in the rabbit liver homogenate in a concentration-dependent manner. It alone did not affect the MDA levels in the absence of .OH. These results indicate that garlic extract is a powerful scavenger of .OH and that heating reduces its activity slightly.