Application of response surface methodology to optimize microwave-assisted extraction of silymarin from milk thistle seeds

Milk thistle (Silybum marianum L.) is an excellent source of silymarin used as an antioxidant. Microwave-assisted extraction (MAE) was employed to extract silymarin from milk thistle seeds. The effects of four independents variables in terms of extraction time, temperature, ethanol concentration, and solid-liquid ratio on the silymarin yield were determined and the optimal conditions for silymarin were evaluated by means of response surface methodology. Correlation analysis of the mathematical regression model indicated that a quadratic polynomial model could be employed to characterize MAE process for the silymarin. Response surface plots showed that these independent variables, except for extraction time, and interactions significantly influenced the extraction yield of silymarin. The optimal extraction parameters to obtain the highest silymarin yield were time duration of 60 min, temperature of 112 degrees C, ethanol concentration of 81.5% (v/v), and a solid-liquid ratio of 1:38 (g/mL). The average experimental silymarin yield under the optimum conditions was found to be 56.67 +/- 1.36 mg/g, which agree with the predicted value of 57.40 mg/g. MAE method was applied successfully to extract silymarin from milk thistle seeds. (C) 2009 Elsevier B.V. All rights reserved.