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Complexes of amylose or high-amylose corn starch (HACS) with genistein were prepared by the acidification of an alkali solution to yield a V 6IotaIotaIota structure. The amylose-genistein complexes exhibited significantly higher genistein content (11 mg/100 mg of complex) than HACS-genistein complexes (9 mg/100 mg of complex). The effect of genistein on the amylose complexes was examined in different genistein-amylose ratios, and a model for genistein organization in the amylose complexes was suggested. The complexes were stable at different pH values, with <10% of the complexed genistein released, and were stable at 30 and 50 degrees C. Lower stability was observed at 80 degrees C as shown by the extensive release of genistein. All complexes showed high retention of genistein in simulated stomach conditions and released genistein upon digestion in pancreatin solution. It is therefore suggested that the complexes can be used as carriers for the slow release of genistein.

Soy isoflavones, present in many processed soy foods, are known for their phytoestrogenic and antioxidant activities. The aim of this work was to study the kinetics of genistein and daidzein degradation at elevated temperatures and to follow changes in their antioxidant activity. Daidzein and genistein in model solutions (pH 7 and 9) were thermally treated at 120 degrees C or incubated at 70, 80, and 90 degrees C. Isoflavone degradation was observed at all temperatures, with apparent first-order kinetics at 70-90 degrees C, and E(a) = 8.4 and 11.6 kcal/mol at pH 9, respectively. Microcalorimetric stability tests showed a similar pattern of degradation, however, with higher E(a) (genistein, 73.7 kcal/mol; daidzein, 34.1 kcal/mol) that may be attributed to the anaerobic conditions. The antioxidant activity of incubated isoflavone solutions, followed by the ABTS test, decreased rapidly at pH 9 for genistein, whereas only moderate reduction was observed for daidzein (pH 7 and 9) or genistein at pH 7. This may indicate different degradation mechanisms for genistein and daidzein.