Abstract: The ultraviolet (UV) absorption characteristics of five Tyr-containing dipeptides (Tyr-Tyr, Tyr-Phe, Phe-Tyr, Tyr-Ala, and Tyr-Ser) were investigated, and their antioxidant activities were evaluated and compared using reducing power assay, cyclic voltammetry and 2,2’-azobis(2-amidinopropane)dihydrochloride (AAPH)-induced liposomal oxidation system. The aim was to explore their influential factors and the distinction and correlation between the antioxidant activities in a homogeneous system and those in a heterogeneous system. The results showed that the amino acid composition and sequence of these dipeptides had a significant influence on their UV absorption characteristics, electron-donating capacity and lipid oxidation inhibitory effect, while the amount of phenolic hydroxyl group played a determinant role in the antioxidant activity. Compared with Tyr-Phe, Phe-Tyr exhibited higher activity in the three antioxidant assays. In the liposomal system, the inhibition of lipid oxidation by these dipeptides were significantly correlated (P < 0.05) with their electron-donating capacity as well as their lipophilicity or hydrophilicity.

Key words: antioxidant; tyrosine; dipeptide; liposome; cyclic voltammetry