Determination of in vitro Antioxidant and Radical Scavenging Activities of Different Extracts of Allium sativum (Garlic)

Abstract

Allium sativum (Garlic) is indigenous to Asia, but largely cultivated in Nigeria. It has acquired a reputation in folklore as a formidable prophylactic and therapeutic agent. This study was undertaken to evaluate the in vitro antioxidant activity of three extracts ( aqueous (AE), ethyl acetate (EA) and petroleum ether (PE)) of garlic using two antioxidant tests; ferric ion reducing power and H2O2 scavenging capacity. The reductive power of each extract was found to be directly proportional to its concentration (0.2 mg/ml - 1 mg/ml) which followed the pattern AE > EA > PE showing the strongest to the least strong antioxidant activity. The reductive power of ascorbic acid as the standard was compared with those of the extracts and was found to be significantly higher (p < 0.05) at all concentrations except 0.6 mg/ml of the aqueous extract. Similarly, ascorbic acid showed strong H2O2 scavenging activity when compared to the extracts (p < 0.05). The % H2O2 inhibition ranged from 67-73, 40-50 and 25-35 for AE, EA and PE extracts respectively. Furthermore, the extracts demonstrated high antioxidant activity against hydrolytic rancidity of crude palm oil by virtue of the low acid value they showed in a concentration dependent manner. The acid values ranged from 4.74 through 5.50 viz. ascorbic acid < AE < PE < EA. These results indicate that garlic prevents lipid peroxidation and radicalic chain reactions. At the same time, the aqueous extract revealed more effective antioxidant capacity than the EA and PE extracts , hence this encourages the culinary use of garlic.