New method to evaluate water-soluble antioxidant activity based on protein structural change.

A simple method to evaluate antioxidant activities of water-soluble ingredients of foods has been developed. Protective effects of antioxidants against hypochlorite radical or hydroxyl radical have been studied by comparing changes in absorbance of myoglobin (a standard reference) at 409 nm. Protective ratio, defined by absorbance changes of myoglobin with or without the antioxidant, was a good indicator to quantitatively evaluate the antioxidant activity against the hypochlorite radical or the hydroxyl radical, respectively. Radar charts indicating the antioxidant activities against DPPH (1,1-diphenyl-2-picrylhydrazyl), hypochlorite radical, and hydroxyl radical clearly differentiated the characteristics of five antioxidants including carnosine, glutathione, and vitamin C. By comparison of the radar charts, antioxidant activity of bonito meat hydrolysate was found to have similar characteristics to that of carnosine. The simple method proposed in this study would be useful for evaluating and characterizing the activities of water-soluble antioxidants contained in various food materials.