Study On Constitutes Of Milk Thistle Seeds By Microwave-assisted Extraction

Milk thistle seeds contain oil, silymarin, protein and other constitutes. Milk thistle seed oil is contained of much nourishment and used as food. Extracts of milk thistle (silybum marianum L.) seeds have a long tradition for treating liver ailments. Silymarin consists of a large number of flavonoligans, including silibinin, isosilibinin, silicristin and silidianin. Recently there were also several studies conducted with silymarin against oxidative stress, inflammatory responses and benzoyl peroxide-induced tumor promotion in mice. It has proven useful for its anti-inflammatory and anti-carcinogenic properties.Microwave-assisted extraction (MAE) is a new technique which was combined with traditional solvent extraction. MAE was manifested to be a simple device, high extraction efficiency, low consumption of agent and time as well as low environmental pollution and so on. MAE allows rapid delivery of thermal energy to target objects, thus minimizing overcooking commonly experienced in conventional thermal processing. MAE was applied for the extraction of milk thistle seed oil and silymarin, and may overcome some limitations of the exiting processes. Experiment contents and results are listed as follows:MAE method was employed to extract milk thistle seed oil. Based on the results of single factor experiments, orthogonal experiments were introduced to optimize the extracting process, and optimum paramerters were obtained as following: extraction time of 4min, microwave power of 560W, and liquid-solid ratio of 7:1. Compared with soxhlet extraction method (SE), the results show that extraction efficiency can be achieved more than 90% and the time is only 1/150 of time of SE. The experiment results will help to impel industrialization of MAE. And quality of oil had been also studied according to GB/T5009.37-2003.Based on experimental data of preliminary study, a comparing experiment between MAE and reflux heating extraction (RHE) to extract silymarin from milk thistle seeds was conducted. Response surface methodology (RSM) was employed to study the effects of extraction time, extraction temperature, ethanol concentration and solid-liquid ratio on silymarin yield, and to determine the optimal extraction process. A mathematical regression model was established to predict the extraction yield of silymarin accurately. The optimum extraction process was obtained as follows: extraction time of 60min, extraction temperature of 112°C, 81.5% ethanol concentration (v/v), solid-liquid ratio 1:38 (g/mL). Under such conditions, the experimental value of the average silymarin yield after extraction for three times was 56.67mg/g. A comparison among MAE,SE and RHE indicates that MAE is a potential alternate method for the extraction of silymarin from milk thistle seeds.The kinetic and thermodynamic mechanisms were also studied in MAE processes, and RHE was performed for comparison study. Knowledge of extraction mechanism allows predicting a possible inhibition or enhancement of extraction yield. The results showed that the reaction order number of both MAE and RHE was first. The activation energy of MAE was nearly 1/5 that of RHE. The average apparent rate constant of MAE was 48 times that of RHE. Based on the Fick's diffusion law and used the electromagnetic-enhanced diffusion theory, a kinetic model has been developed for MAE under closed vessel condition. The effects of extraction temperature, extraction time and microwave power on MAE were modeled. Except for the power, the experimental and modeling data of MAE were closed to each other and their diffusion coefficients were almost the same, indicating that the model developed was reasonable.A few of simple models were applied to calculate partition coefficients and the thermodynamic parameters (⊿H~0,⊿S~0 and⊿G~0 on the silymarin of MAE and RHE. The results showed that MAE and RHE were increasing endothermic and entropy processes. With the help of scanning electron microscopy (SEM), the cell microstructures of samples extracted by MAE, RHE and raw samples were observed. The results revealed that the increased efficiency and yield of silymarin by MAE could be mainly attributed to the subsequent cell change resulting from the superheating effect during MAE. The values of⊿G~0 indicated that the reactions of silymarin by MAE were more spontaneous than RHE.