Silybum marianum pericarp yields enhanced silymarin products

Abstract

An improved method for the purification of silymarin, the flavonolignan complex from the fruits of milk thistle, Silybum marianum, is reported. The method enables a more efficient extraction of silymarin from the pericarp after it has been separated mechanically from the rest of the fruits. Accelerated solvent extraction (ASE) was employed for each extraction procedure. Quantitation of the eight major silymarin components in the pericarp extract was compared to that of the whole fruit extract using two orthogonal analytical methods. The pericarp extract showed higher silymarin content (2.24-fold by HPLC and 2.12-fold by qHNMR) than whole fruit extract using acetone as an extraction solvent following defatting with hexane. Furthermore, the mg/g recovery of silymarin major components was not diminished by eliminating the hexane defatting step from the pericarp extraction procedure. The efficiencies of acetone, ethanol, and methanol as extraction solvents were compared. Methanol pericarp extract showed the highest content of the silymarin major components, 2.72-fold higher than an extract prepared from the whole fruits using acetone. Finally, all of the major silymarin components showed a higher w/w content in the pericarp extract than in a commercial extract.

Keywords: Accelerated solvent extraction; Pericarp; Silybum marianum; Silymarin.

Fig. 1

Chemical structures of the silymarin marker compounds.

Fig. 2

Silybum marianum fruits pericarp detached from the kernels. Left column: whole fruits, middle column: kernels, and right column: pericarps.

Fig. 3

A: HPLC chromatograms showing the analysis of silymarin components contained in Silybum marianum pericarp (front, solid line), kernel (middle, dashed line), and soaking water (back, dotted line). Quantitation data for pericarp and kernel are found in Table 2 extracts 2 and 3 respectively. B: HPLC chromatograms showing the analysis of silymarin components obtained by extraction of Silybum marianum whole fruits (front, solid line) and pericarp (back, black filled peaks). Quantitation data for these extracts are found in Table 2, extracts 1 and 2 respectively. C: HPLC chromatograms showing the content of silymarin components obtained by extracting pericarp with acetone (front, solid line), ethanol (middle, dotted line), and methanol (back, dashed line). Quantitation data for these extracts are found in Table 2, extracts 2, 4 and 5 respectively.

Fig. 3

A: HPLC chromatograms showing the analysis of silymarin components contained in Silybum marianum pericarp (front, solid line), kernel (middle, dashed line), and soaking water (back, dotted line). Quantitation data for pericarp and kernel are found in Table 2 extracts 2 and 3 respectively. B: HPLC chromatograms showing the analysis of silymarin components obtained by extraction of Silybum marianum whole fruits (front, solid line) and pericarp (back, black filled peaks). Quantitation data for these extracts are found in Table 2, extracts 1 and 2 respectively. C: HPLC chromatograms showing the content of silymarin components obtained by extracting pericarp with acetone (front, solid line), ethanol (middle, dotted line), and methanol (back, dashed line). Quantitation data for these extracts are found in Table 2, extracts 2, 4 and 5 respectively.

Fig. 4

A. ¹H NMR spectra of silybin (A & B) (a), silydianin (b), silychristin A (c), isosilychristin (d), and taxifolin (e). B. ¹H NMR spectra for whole fruit (red, front) and pericarp (blue, back) extracts (expanded region, 0.5 – 7.5 ppm). Quantitation data for these extracts are presented in Table 3.

Fig. 5

Graphical representation of the quantitation data presented in Table 2 for extracts 1 (T1), 2 (T2), 4 (T3), 5 (T4), and 6 (T5).