Optimization of Microwave Assisted Extraction of Total Triterpenoid in Diospyros kaki Leaves Using Response Surface Methodology

Abstract

The triterpenoid in Diospyros kaki leaf has multiple pharmacological activities. Thus a fast and efficient method for preparation of triterpenoid from Diospyros kaki is very important. In this study, several extraction methods (Soxhlet extraction, reflux extraction, ultrasound assisted extraction, microwave assisted extraction) were compared. Microwave assisted extraction was found to be the most effective method and then the extraction conditions were further optimized using central composite design. The results showed extraction time and solvent to solid ratio were statistically most significant factors on total triterpenoid extraction. The optimal conditions were calculated as extraction under microwave power 365.3 W for 13.05 min, with 60.27 % ethonal as solvent at a solvent to solid ratio 22.26. Under the optimal conditions, the yield of total triterpenoid obtained experimentally (61.82 mg/g dry leaves) was close to its predicted value of 71.43 mg/g dry leaves, which suggested the mathematical model was fit well with the experimental data of total triterpenoid extraction. In addition, the HPLC assay implied that five triterpene acids (ursolic acid, oleanic acid, barbinervic acid, rotungenic acid and 24-hydroxy ursolic acid) were abundant in the extracts