Application of response surface methodology for the optimization of the extraction of triterpenoid saponins from Azadirachta excelsa leaves

Abstract

Azadirachta excelsa originates from the Meliaceae family and is often subjected to bioactivity studies due to the presence of various types of compounds such as phenolics, flavonoids and terpenes. Triterpenoid saponins are diverse groups under terpenoids and are secondary metabolites produced by plants for carrying out antagonistic and mutualistic interactions. These compounds are extensively investigated for bioactivities such as anticancer, antimicrobial and pesticidal properties due to their wide range of action mechanism. This study aimed to optimize A. excelsa leaves extraction process using response surface methodology (RSM) for obtaining extract with high extract yield and triterpenoid saponins content. The independent variables selected for the extraction process included temperature, ethanol-to-chloroform ratio, time and sample-to-solvent ratio. The individual and interactional effects of extraction parameters on the yield of extract and triterpenoid saponins content were evaluated using Central composite design (CCD) of RSM. The responses were predicted using second order polynomial model. One-way analysis of variance (ANOVA) revealed correlation coefficients (R2) of developed model for yield of extract and triterpenoid saponins contents were 0.9792 and 0.9509. High F-statistics value and lower p-value (<0.0001) revealed sample-to-solvent ratio had major effect on extract yield and triterpenoid saponins content. Larger surface area exposure of plant material to solvent elevates interaction between solid and liquid matter resulting in higher extract yield and triterpenoid saponins content. The optimum extraction conditions were 45 °C of temperature, ethanol-to-chloroform ratio of 90:10, 60 min of extraction duration, 1:50 g/mL of sample-to-solvent ratio. The actual yield of extract and the triterpenoid saponins contents at optimum extraction conditions were 10.63% and 0.45% respectively. These values differed by 2.9 % for yield of extract and 11.3 %, for triterpenoid saponins content from the values predicted by the model. Some plants triterpenoid saponins have demonstrated pesticidal properties. This study was conducted as an initial step in the potential utilization of A. excelsa leaves extract as a natural pesticide. Results obtained in this study can be utilized as a guidance for extraction of A. excelsa leaves and to compare the extraction efficiency of established method with possible methods developed in future.