Effects of different heat treatments on antioxidant activity and polyphenols in root vegetables

Abstract

　Root vegetables are generally cooked by boiling or other heat treatments. In this study, we compared raw and heat-treated versions of the following root vegetables: carrots, radishes, and burdock root. The heat treatment was one of the following four: boiling (10 or 20 minutes), steaming, microwave heating, and hot air drying. The antioxidant activity and polyphenol content of these raw and heat-treated root vegetables were measured. The results showed that the raw root vegetables differed in antioxidant activity and polyphenol content. Among the three root vegetables, burdock showed the highest antioxidant activity and polyphenol content. It was also found that the antioxidant activity and polyphenol content of the root vegetables varied depending on the heat treatment methods. Furthermore, boiling tended to decrease the antioxidant activity and polyphenol content of the root vegetables, while microwave heating treatment did not decrease them to any significant extent. The correlation between the antioxidant activity and polyphenol content showed that the contribution of polyphenols to antioxidant activity varied with the type of root vegetable.