Preparative Isolation of Isoflavones from Defatted Soy Flakes

Abstract

Defatted soy flakes (DSF) were used as the starting material for the preparative isolation of isoflavones in this study. First, the crude DSF extracts were prepared using an extractor with solvent refluxing, operated under optimal extraction conditions (using 500 mL 80% ethanol aqueous for 3 h per 100 g DSF). The extraction yield was about 10% and the purity of isoflavones was about 2.0–2.5 wt%. Before the isolation operations, the extracts were dissolved in deionized water. The isolation procedures included the method of liquid–liquid extraction and the method of column chromatography. For the method of liquid–liquid extraction using a mixed solvent of 10% n‐butanol and 90% ethyl acetate operated under the optimal extraction conditions, the purity and yield of isoflavones were ∼35% and ∼70%. For the method of column chromatography, XAD‐7HP and XAD‐4 adsorbents with different polarities were used as the packing materials. For the XAD‐4 column, a part of non‐polar impurities was efficiently separated with the majority of isoflavones by a proper step gradient elution, which resulted in an efficient isolation: the purity and yield of isoflavones were ∼58% and ∼89%. In comparison, the method of column chromatography using XAD‐4 adsorbents achieved both the highest purity and yield, and was found to be the best isolation method in the current isolation stage.

Keywords:

• Defatted soy flakes
• Isoflavones
• Preparative isolation
• Liquid–liquid extraction
• Column chromatography

Acknowledgment

The authors wish to thank the National Science Council of Taiwan for the financial support under grant No. NSC 93‐2214‐E‐224‐004.