Extraction of co-products from biomass: example of thermal degradation of silymarin compounds in subcritical water.

In an effort to increase revenues from a given feedstock, valuable co-products could be extracted prior to biochemical or thermochemical conversion with subcritical water. Although subcritical water shows significant promise in replacing organic solvents as an extraction solvent, compound degradation has been observed at elevated extraction temperatures. First order thermal degradation kinetics from a model system, silymarin extracted from Silybum marianum, in water at pH 5.1 and 100, 120, 140, and 160 degrees C were investigated. Water pressure was maintained slightly above its vapor pressure. Silymarin is a mixture of taxifolin, silichristin, silidianin, silibinin, and isosilibinin. The degradation rate constants ranged from 0.0104 min(-1) at 100 degrees C for silichristin to a maximum of 0.0840 min(-1) at 160 degrees C for silybin B. Half-lives, calculated from the rate constants, ranged from a low of 6.2 min at 160 degrees C to a high of 58.3 min at 100 degrees C, both for silichristin. The respective activation energies for the compounds ranged from 37.2 kJ/gmole for silidianin to 45.2 kJ/gmole for silichristin. In extracting the silymarin with pure ethanol at 140 degrees C, no degradation was observed. However, when extracting with ethanol/water mixtures at and 140 degrees C, degradation increased exponentially as the concentration of water increased.

Pressurized water versus ethanol as a Silybum marianum extraction solvent for inhibition of low-density lipoprotein oxidation mediated by copper and J774 macrophage cells.

Silybum marianum contains flavonolignans, termed silymarin (SM), that are therapeutic agents for many inflammation-based diseases including atherosclerosis. Oxidation of human low-density lipoprotein was induced by CuSO4 or J774 macrophage cells and measured by the formation of thiobarbituric acid reactive substances (TBARS). SM was extracted by pressurized hot water (PHWE) or ethanol, and the effects of these extracts on TBARS formation were evaluated in comparison with those of SM preparations made from blending masses of individual flavonolignan standards in ratios identical to those of the water and ethanol extracts. Ethanol-extracted SM and its blended counterpart inhibited the generation of TBARS by 82% and 43%, respectively, at 150 mumol/L doses. TBARS levels in the presence of 150 micromol/L of the PHWE and its blended SM counterpart were reduced by 84% and 38%, respectively. Extracts from milk thistle fruit displayed higher protective effects than blended SM solutions of the same concentration with an identical compositional makeup. The appearance of degradation peaks in the water extract did not create any cytotoxic effects. Results of this study confirm that PHWE can be used to extract flavonolignans from milk thistle and that these extracts may possess therapeutic potential different from or beyond that of traditional organic solvent preparations.

Batch solvent extraction of flavanolignans from milk thistle (Silybum marianum L. Gaertner).

Seeds of milk thistle (Silybum marianum L. Gaertner) contain silymarins and ca. 25% (w/w) of oil. A pre-treatment step involving refluxing with petroleum ether is usually performed before extraction of the silymarins using organic solvents. This paper compares the extraction of whole and defatted milk thistle seeds in various solvents as a function of temperature. The extraction of whole seeds of milk thistle with water at 50, 70 and 85 degrees C was also examined: the yield of silymarin increased with increasing water temperature. In most cases, ethanol at 60 degrees C recovered the largest quantities of silymarins. However, boiling water proved to be an efficient extraction solvent for the more polar silymarins such as taxifolin and silychristin, even when using whole seeds. Extractions of defatted seed meal with boiling ethanol returned maximum yields of 0.62, 3.89, 4.04, and 6.86 mg/g defatted seed of taxifolin, silychristin, silybinin A and silybinin B, respectively. When extracting defatted seed meal with ethanol, yields of taxifolin, silybinin A and silybinin B were, respectively, 6.8-, 0.95-, 1.7- and 1.6-fold higher than when extracting whole seeds. When extracting with boiling water, the yields of silychristin, silybinin A, and silybinin B were 380, 47 and 50% higher for whole seeds compared with defatted seeds.

Extraction of nutraceuticals from milk thistle: I. Hot water extraction.

Milk thistle contains compounds that display hepatoxic protection properties. We examined the batch extraction of silymarin compounds from milk thistle seed meal in 50, 70, 85, and 100 degrees C water as a function of time. After 210 min of extraction at 100 degrees C, the yield of taxifolin was 1.2 mg/g of seed, a 6.2-fold increase over the results obtained in a Soxhlet extraction with ethanol on pretreated (defatted) seeds. Similarly, the yield of silychristin was 5.0 mg/g of seed, a 3.8-fold increase. The yields of silybinin A and silybinin B were 1.8 and 3.3 mg/g of seed, respectively, or roughly 30% of the Soxhlet yield. 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 degrees C, while the less polar silybinin was favored at 100 degrees C.

Extraction of nutraceuticals from milk thistle: part II. Extraction with organic solvents.

Seeds from milk thistle (Silybum marianum Gaert L.) contain flavanolignan and dihydroflavanol compounds that have interesting and important therapeutic activities. The recovery of these silymarin compounds generally involves a two-step defatting and extraction process using organic solvents. This study examined the batch, single-stage extraction of whole and defatted seeds using ethanol, methanol, acetonitrile, and acetone as the solvents. In extracting defatted milk thistle seeds with organic solvents, extraction with ethanol resulted in the highest silymarin yield, although some potential degradation was observed. The maximum yields of taxifolin, silychristin, silydianin, silybinin A, and silybinin B in ethanol were 0.6, 4.0, 0.4, 4.0, and 7.0 mg/g of defatted seed, respectively. However, if silybinin A were the diastereoisomer of choice, methanol would be the preferred extraction solvent because it yielded the highest silybinin A to silybinin B ratio. Interestingly, lipid removal is an important extraction step, because defatted material yields twice the silymarin concentration.