Antioxidant activity of thiosulfinates derived from garlic

Garlic extract significantly inhibited the oxidation of methyl linoleate in homogeneous acetonitrile solution, whereas the antioxidant effect of allicin-free garlic extract, prepared by removing allicin by preparative HPLC, was much lower than that of the garlic extract. These results suggest that the antioxidant properties are mostly attributed to the presence of allicin in the garlic extract. Allicin, a major component of the thiosulfinates in garlic extract, was found to be effective for inhibiting methyl linoleate oxidation, but its efficiency was less than that of alpha-tocopherol. Next, the reactivity of allicin toward the peroxyl radical, which is a chain-propagating species, was investigated by direct ESR detection. The addition of allicin to 2,2'-azobis(2,4-dimethylvaleronitrile)-peroxyl radical solution caused the signal intensity of the peroxyl radical to dose-dependently decrease, indicating that allicin is capable of scavenging the peroxyl radical and acting as an antioxidant. Finally, we studied the structure - antioxidant activity relationship for thiosulfinates and suggested that the combination of the allyl group ( - CH2 CH= CH2) and the - S(O) S - group is necessary for the antioxidant action of thiosulfinates in the garlic extract. In addition, one of the two possible combinations, - S( O) S - CH2 CH= CH2, was found to make a much larger contribution to the antioxidant activity of the thiosulfinates than the other, CH2= CH - CH2 - S(O) S-.