Eriocitrin, a flavonoid glycoside present in citrus fruit. It is certified that there is no problem with a safety to humans.A food material having a high concentration of eriocitrin as an antioxidant ingredient derived from citrus fruits can industrially be produced at a low cost. Further, the product is a food material having a high concentration of eriocitrin and having less bitter and rough tastes. Accordingly, when this material is added to beverages or foods, beverages or foods having less unpleasant bitter and rough tastes and having a high antioxidant effect can be obtained. Consequently, foods which help prevent diseases derived from habits of daily life can be provided.