Determination of Antioxidant Activity in Garlic (Allium sativum) Extracts Subjected to Boiling Process in vitro

Garlic is a vegetable known to be a good antioxidant food resource around the world. Several studies on the antioxidant activity of garlic, mainly conducted using one or two methods, have been reported. However, comparison of the antioxidant activity of garlic before and after cooking is rarely reported. In this study, we compared the antioxidant activity of garlic aqueous and methanol extracts processed before and after boiling to mimic the cooking process. By testing the antioxidant activities of the extracts in different chemical mimic systems in vitro, namely, ABTS [2, 2’-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid)] and DPPH (2, 2-diphenyl-1-picrylhydrazyl) radical scavenging activities, reducing power, and metal chelating ability, we found the following data: (1) no significant difference was observed on the ABTS radical scavenging activities of garlic aqueous and methanol extracts before and after boiling process; (2) the reducing power of garlic aqueous and methanol extracts decreased by 25.9% and 14.1%, respectively, whereas the metal chelating activity of boiled garlic aqueous extracts increased by 54.7%; and (3) DPPH radical scavenging test may not be suitable to examine the garlic extracts. In addition, the ABTS radical scavenging activities of garlic extracts were very stable at pH ranges similar in human bodies, and both sulfhydryl and phenolic compounds were probably responsible for the antioxidant ability of garlic. The boiling process destroyed only a small part of garlic bio-ingredients related to antioxidant activity properties.