Response Surface Methodology for Optimizing Parameters of the Ultrasound-Assisted Extraction of Total Phenolic Content of Oxalis corniculata Leaves

Oxalis corniculata Linn. Oxalidaceae) is one of the significant medicinal plants to treat liver diseases, jaundice, and urinary tract disorders and skin diseases in traditional medicine. The aim of this study was to use ultrasound assisted extraction method for extracting polyphenolic compounds from O. corniculata leaves, and also to optimize the various extraction parameters, i.e. solvent concentration, time of extraction and operating temperature. The central composite rotatable design (three factor-five level) was used to develop response surface methodology (RSM) model and to optimize the best extraction conditions of O. corniculata leaves. The analysis revealed that all the independent variables were significant (p < 0.05) to the responses which implied that the extraction parameters used in this study were vital in the optimisation process. The R2 values of the response, i.e. total phenolic content (TPC) was 0.9965 which indicated that the quadratic polynomial models, developed were satisfactorily accurate to be used in the analysis of the interactions of the parameters (response and the independent variables). The optimum conditions found in RSM could be applied in future upscale extraction of the leaves of O. corniculata taking into consideration the temperature, extraction time and solvent for the economical analysis.