Abstract

Milk thistle (Silybum marianum L.) seed meal is extracted for the flavonolignans, silychristin, silydianin, silybinin A, silybinin B, isosilybinin A and isosilybinin B, which are collectively known as the silymarin complex. To obtain the flavonolignans, the meal is usually treated with successive washes of petroleum ether to remove the lipids, followed by extraction of the flavonolignans with ethanol. This work examines the possible replacement of petroleum ether and ethanol by water or other aqueous solutions in these processes. To replace petroleum ether, pretreatments with 1.2% NaOH (w/w), 1.5% H₂SO₄ (w/w), 2% NaHCO₃ (w/w), 0.14% cellulase and water were investigated. Of these pretreatments, 1.5% H₂SO₄ and water produced similar flavonolignan yields as petroleum ether. Results established that pretreating the milk thistle seed meal with 1.5% H₂SO₄ (w/w) at 50 °C for 18 h could replace the petroleum ether pretreatment. In addition, it was shown that similar amounts of flavonolignan could be recovered with a 1.5% H₂SO₄/water (100 °C) extraction as with a petroleum ether/ethanol extraction. Although cellulase pretreatment was not examined extensively, significant advances in cellulase effectiveness and cost have occurred in the past few years by companies such as Genencor International and Novozymes. These advances should help to make enzyme use for cellulose conversion, as well as extraction pretreatment, technically and economically feasible.

Keywords: Milk thistle; Pretreatment; Silymarin; Flavonolignans; Water extraction

Article Outline

1. Introduction

2. Methods

2.1. Plant material

2.2. Chemicals

2.3. Pretreatment studies

2.4. Hot water extraction

2.5. HPLC analysis

2.6. Statistical analysis

3. Results

3.1. Initial pretreatment screening

3.2. Temperature effects on selected pretreatments

3.3. Effects of pretreatment time on selected pretreatment techniques

3.4. Combining H₂SO₄ pretreatment with water extraction time

4. Discussion

References