Synergistic antioxidant activity of plant compositions contained in Chatuphalathika herbal recipe: Terminalia chebula Retz. var. chebula, Terminalia arjuna Wight and Arn., Terminalia bellirica (Gaertn.) Roxb., and Phyllanthus emblica L.

The work sought to investigate, using response surface analysis, the synergistic antioxidant activity among four plants—Terminalia chebula Retz. var. chebula, Terminalia arjuna Wight and Arn., Terminalia bellirica (Gaertn.) Roxb., and Phyllanthus emblica L.—which are comprised in the Chatuphalathika recipe. The response surface analysis of the four-component simplex lattice design was performed using the combination index method. The mass ratio of the four plants was varied. The total phenolic content, antioxidant activity based on the half-maximal inhibitory concentration (IC50) from 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays were monitored and used to calculate the combination index value. Results showed that the total phenolic content was high and the IC50 values from DPPH and FRAP assays were low when T. chebula, T. arjuna, and T. bellirica were used without P. emblica. Synergistic antioxidant activity was also observed among them. The mixture of T. chebula, T. arjuna, and T. bellirica without P. emblica gave better synergistic antioxidant activity than when P. emblica was incorporated. The data from this work could be used to select the suitable mass ratio of the plants for the preparation of the supplementary health products in further work.