Comparison of extraction solvents and techniques used for the assay of isoflavones from soybean

The impact of extraction solvents and techniques on the assay of isoflavones from soybean was investigated. This systematic study was undertaken to address substantial variations in the solvents and procedures used for the extraction of isoflavones from soybeans by different research groups as described in the recent peer-reviewed published literature. Comparison of four previously optimized and commonly deployed solvent mixtures (acetonitrile:water 58:42 (v/v); ethanol:water 70:30 (v/v); methanol:water 90:10 (v/v); superheated pressurized water) was carried out for the extraction of isoflavones. In addition, we also examined the extraction efficiencies of three additional new solvent mixtures (dimethyl sulphoxide:acetonitrile:water, 5:58:37 (v/v/v); dimethyl sulphoxide:ethanol:water, 5:70:25 (v/v/v); Genapol:water 5:95 (v/v)) for the extraction of isoflavones from soybeans. Assessments of six commonly used extraction techniques (shaking, vortexing, sonication, stirring, Soxhlet, and pressurized liquid extraction (PLE)) with an optimized extraction solvent mixture was also performed. Both, the total isoflavones content and the isoflavones HPLC profile varied significantly with different extraction solvents and techniques. Optimum total isoflavones recoveries from soybean samples were obtained with dimethyl sulphoxide:ethanol:water (5:75:25, v/v/v) solvent mixture using a PLE. Intermediate extraction recoveries of total isoflavones from soybean samples were obtained with the other extraction solvent mixtures and techniques tested. The extraction efficiencies of isoflavones with shaker, vortex, stirring, and Soxhlet were between 65% and 70% as compared to PLE. Total isoflavones extracted by the sonication procedure was 93.3% as compared to PLE.