Effects of cooking methods and food ingredients on the antioxidant activity of onion peel addition recipes

<p>Quercetin is known to have high antioxidant activity. The onion peel (OP) contains high concentrations of quercetin. Therefore, it is considered that the antioxidant activity works in the body by ingesting OP. However, OP must be cooked with other foods for ingestion. It is suggested that cooking changes the OP antioxidant activity. Therefore, the purpose of this paper is to examine the effect of cooking on the antioxidant activity of OP.</p><p>Forty-eight recipes with OP powder added were considered and cooked. In addition, the recipes were cooked without the addition of OP powder. A total of 96 dishes were decomposed into sample solutions. The fat soluble and water-soluble antioxidant activity of the sample was measured by the DPPH (1,1-diphenyl-2 picrylhydrazyl) method. Furthermore, the 51 ingredients used in each recipe were calculated based on the Standard Tables of Food Composition in Japan. The relationship between the measured antioxidant activity of OP and cooking method, and contained components was determined. From this relationship, the factors affecting the antioxidant activity of OP powder were investigated.</p><p>The antioxidant activity of recipes by adding OP powder increased by 36 recipes (75%) for fat-soluble and 27 recipes (56%) for water-soluble. The average rate of increase in antioxidant activity by OP was 1.34 ± 0.48 for fat-soluble and 1.06 ± 0.29 for water-soluble. The fat-soluble antioxidant activity was significantly higher by the addition of OP (p < 0.01), and no significant difference was shown in water solubility.</p><p>In the "Stir-fried" cooking method by OP, the fat-soluble antioxidant activity showed a significantly high value (mean value: 1.66 ± 0.67) (p < 0.05). Regarding food ingredients, insoluble dietary fiber, water-soluble dietary fiber, total dietary fiber (p < 0.01), and potassium, iodine, and iron (p = 0.01, 0.01, 0.05, respectively) significantly increase fat-soluble antioxidant activity. Molybdenum (p = 0.05) significantly increase water-soluble</p>