University of Arkansas, Fayetteville


High value specialty chemicals are usually obtained from natural products by extracting with generally regarded as safe (GRAS) solvents. Because organic solvents are quite often used, high operating and disposal costs often occur. When compared to traditional solvents, water can be viewed as an interesting alternative because of its low operating and disposal costs. Milk thistle contains compounds (taxifolin, silychristin, silydianin, silybinin A and silybinin B) that display hepatoxic protection properties. This paper examines the batch extraction of silymarin compounds from milk thistle seed meal in 50'C, 70'C, 85'C and 100'C water as a function of time. For taxifolin, silychristin, silybinin A and silybinin B, extraction with 100' C water resulted in the highest yields. After 210 min of extraction at 100'C, the yield of taxifolin was 1.2 mg per g of seed, while the yields of silychristin, silybinin A and silybinin B were 5.0, 3. 7 and 6.5 mg per g of seed, respectively. The overall diffusion coefficients for the four compounds increased with temperature and ranged from 0.14 x 10^ 10 to 4 x10 ^ 10 m2 /sec, indicating that the diffusion coefficients could potentially be used for quantitative comparisons of extraction conditions. The ratios of the extracted compounds, and particularly the ratios at long extraction times, showed that the more polar compounds (taxifolin and silychristin) were preferentially extracted at 85'C, while the less polar silybinin was preferentially extracted at 100'C.