The Preparation of Preserved Shallot Powders and a Pilot Study of the Antioxidative Effect of Their Aqueous Extracts on the Formation of Hydroxyl Radical Species

Abstract

In order to preserve the nutrients in shallots, after harvest, various protocols, including incubation, drying or lyophiliza-tion of the shallot are developed in this study. Using aqueous extracts of ground shallot powders, this study examines the antioxidative properties of shallots on the formation of hydroxyl radical species (• OH) generated via a Fenton-type reaction. A ribose degradation assay shows that all aqueous extracts of shallot prepared in this study exhibit enhanced levels of • OH, suggesting that processed shallot, like strong reductants such as ascorbate, has a strong reducing power, which converts Fe 3+ to Fe 2+ in a Fenton's reaction and increases the levels of • OH. A DNA integrity assay shows that fragmentation of super-coiled plasmid DNA, pGEM-7Zf(-), by • OH is diminished in the presence of all shallot aqueous extracts, albeit to various extents. Finally, electron paramagnetic resonance (EPR) experiments show that lyophilized shallot completely scavenges • OH, as evidenced by the disappearance of the EPR-active reaction product generated between spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), and • OH. The results of this study show the potential of a daily intake of preserved shallot to boost antioxidative protection against the toxicity of • OH or any other damaging radicals.