Extraction of silymarins from milk thistle, Silybum marianum, using hot water as solvent

Extraction solvent plays a crucial role in producing standardized herb products. The use of organic solvent in extraction causes environment and health concern. Water could be an effective extraction solvent in the recovery of active components from plant material because it is non-toxic, environmentally friendly and has a low cost. The extraction of milk thistle (Silybum marianum) seeds yields taxifolin and the silymarin complex, which is composed of silychristin, silydianin, silybinin (representing as silybinin A and silybinin B) and isosilybinin. The extraction of taxifolin and silymarin compounds from ground milk thistle seeds using hot/liquid water as the solvent was carried out on a self constructed dynamic extraction apparatus. The effects of temperature (100, 120, and 140°C) and water flow rate (0.35, 0.45, and 0.72mL/min) on extraction yield were studied. Extraction efficiency was increased with temperature. The maximum yields of the individual flavonoid compounds obtained in extractions at different temperatures, however were slightly different irons each outer. It was observed that the extraction efficiency was increased with increasing water flow rate.; A batch extraction apparatus with stirring was designed to carry out the extraction experiments to better understand the water extraction process and to provide information for modeling. The concentration profiles of the individual silymarin compounds featured three stages, including fast accumulation, approaching the maximum, and concentration reduction stage. Temperature (90, 100, and 120°C), agitation speed (150 and 60 rpm), and particle size (0.4 and 0.7 mm) were shown to affect the duration of each stage and the maximum concentrations of the individual silymarin compounds. The duration of the fast accumulation stage was shortened significantly when the temperature was increased. It was also observed that the duration of the fast accumulation stage was not dependent on the agitation speed. The particle size, which determines the particle surface area and intraparticle diffusion distance, significantly affected the extraction process.; A model was developed to describe the water extraction process. The overall mass transfer coefficient (kpi) for each of the silymarin compounds "as evaluated by simulating the modeling equations. For example, the overall mass transfer coefficients for silychristin, silydianin, silybinin A and silybinin B at 90°C 0.4 mm and 150 rpm were 3.9x10 -5, 2.9x10-5, 5.0x10-5, and 5.6x10-5 cm.min-1, respectively. In addition, the model adequately predicted the fast accumulation, approaching the maximum, and concentration reduction stages during the extraction. The model can he used as a tool to predict the progression of a water extraction process under a variety of conditions.