Distribution of phenolic acids in different tissues of jujube and their antioxidant activity.

Free, esterified, glycosided, and insoluble-bound forms of eight phenolic acids in pulp, seed, and peel of jujube are separated and quantified by high performance liquid chromatography with electrochemical detection (HPLC-ECD). In the whole jujube, p-hydroxybenzoic and cinnamic acids are the most abundant phenolic acids. All quantified phenolic acids are mainly present in jujube peel. Phenolic acids in seed and peel are present in the insoluble-bound form, while, in pulp in the glycosided form, the glycosided and insoluble-bound phenolic acid fractions in jujube pulp represent the highest total phenolic content and the strongest antioxidant activity determined by DPPH and FRAP assays. Our results show that most phenolic compounds with antioxidant activity in different tissues of jujube are present as the glycosided and insoluble-bound forms.