Synergistic Effects of Potentilla fruticosa L. Leaves Combined with Green Tea Polyphenols in a Variety of Oxidation Systems.

Potentilla fruticosa L. leaves are widely used as tea in China, with many commercial "Jinlaomei" teas available in markets. It has been confirmed to possess significant antioxidant activity than that of butylated hydroxytoluene. In this study, the synergistic effects of P. fruticosa leaves extracts (PFE) combined with green tea polyphenols (GTP) were studied to elucidate their use in combination and find specific combinations with least concentrations that enhance the antioxidant activity. Isobolographic analysis indicated that the combination of PFE and GTP demonstrated extensive synergism (22/28 of the tests showed significant synergy) with 3:1 (PFE:GTP) exhibiting the best synergistic effect. Chemical compositions and content of 7 phenolic compounds in PFE, GTP, and their mixtures were evaluated by reverse-phase-high-performance liquid chromatography. While chemical composition did not seem to change after the combination, as no new peaks appeared in the chromatogram, and no existing peaks disappeared. However, the content of (+)-catechin, (-)-epigallocatechin (EGC), and , (-)-epigallocatechin gallate (EGCG) changed. Besides, antioxidant interactions of extracts and compounds were evaluated, EGC with hyperoside exhibited the greatest synergistic effect and the combination of 3:1 exhibited the strongest synergism (DPPH γ = 0.86, ABTS γ = 1.12, FRAP γ = 1.16). Therefore, interaction of phytochemicals may be one reason for the synergistic effects in PFE + GTP, with EGC + hyperoside likely playing an important role. This report provides a theoretical basis for the concomitant use of P. fruticosa blended with GTP, which can be effectively used as a compounded tea, dietary supplements, and substituent of synthetic antioxidant.