Optimization of antifungal extracts from Dracocephalum kotschyi using response surface methodology and evaluations of antifungal effects on Candida albicans

Opportunistic fungi are known as important causes of nosocomial infections. Since drug resistance is one of the main problems when treating the infections, many efforts have been made to develop alternative drugs – herbal compounds, in particular. Dracocephalum kotschyi is a medicinal plant widely used in traditional medicine, which also shows sufficient antifungal activities against different species of Candida. This study aimed to optimize condition for extraction of bioactives from D. Kotschyi and achieve the maximum antifungal properties by adopting response surface methodology (RSM).

A three-factor-five-level central composite rotatable design (CCRD) was employed to determine the effects of extraction time (1-12 hours), temperature (40-80°C), and plant powder to solvent (PP/S) ratio (0.2-0.8%) on well diffusion method (WDM), minimum fungicidal concentration (MFC), and minimum inhibitory concentration (MIC). The methanol extracts were prepared using Soxhlet apparatus, and the antifungal activities against ATCC 1677s Candida albicans were evaluated.

The results showed that the P values of the model for WDM, MFC, and MIC were 0.0062, 0.0111, and 0.0278, respectively. The determination coefficient for WDF, MFC, and MIC were 0.853, 0.770, and 0.721, respectively. In addition, the lack of fit for all responses was non-significant (P value ˃0.05). The optimal extraction parameters included the extraction time of 3.23 hours, PP/S ratio of 0.68 mg/ mL, and temperature of 68˚C.

In sum, RSM with CCRD was found to be an efficient method for designing and optimizing the extraction process. The optimized extracts exhibited an acceptable antifungal effect compared to the predicted effects against C. albicans.