Effects of extraction temperature, ionic strength and contact time on efficiency of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) reverse micellar backward extraction of soy protein and isoflavones from soy flour

BACKGROUND: Soy protein enriched with isoflavones has been linked to various disease-preventing and health-promoting activities owing to the antihypertensive, hypocholesterolaemic, antiobesity and antioxidative properties of isoflavones. The isoflavone profiles of soy-based products are known to be highly dependent on the various chemical and physical treatments to which the products have been subjected. The aim of this research was to increase the efficiency of backward extraction of soy protein and isoflavones from bis(2-ethylhexyl) sodium sulfosuccinate (AOT) reverse micelles by studying the effects of extraction temperature, ionic strength of the aqueous stripping solution and contact time on the amounts of soy protein and isoflavones backward extracted from an AOT/H2O/isooctane reverse micellar system. RESULTS: By modifying the extraction temperature, ionic strength and contact time, 47.0 - 60.2% of protein, 43.3 - 68.4% of daidzin, 43.8 - 74.6% of genistin, 39.0 - 88.8% of glycitin, 20.8 - 92.6% of malonyl genistin, 20.2 - 52.0% of malonyl glycitin, 32.7 - 75.6% of acetyl genistin, 49.7 - 76.8% of daidzein and 19.6 - 38.1% of genistein present in the AOT reverse micellar solution were backward extracted into the aqueous stripping phase. Statistical analysis showed that there were significant linear and interactive effects of temperature and contact time on the backward extraction of daidzin, genistin, glycitin and daidzein. Significant linear and interactive effects of ionic strength and contact time were found in the backward extraction of daidzin and genistin. The backward extraction of genistein was only influenced by contact time and its interaction with temperature. CONCLUSION: This study showed the potential of reverse micelles as a protocol for extracting isoflavones from soy samples for analytical purposes. By modifying the extraction temperature, contact time and ionic strength, soy protein enriched with daidzin, genistin, daidzein and genistein could be produced from soy flour. The results represent an important contribution to current knowledge on utilising reverse micellar extraction in food technology. (c) 2007 Society of Chemical Industry.