We studied the effect of freeze-thaw on isoflavone composition in germinated soybeans, particularly the conversion of aglycones, the isoflavone monomers with high biological activity. Germinated soybeans were frozen at -20 °C, -80 °C, and -196 °C respectively, and then the frozen samples (-20 °C) were thawed at 4 °C, 10 °C, and 25 °C respectively. Results showed total isoflavone increased after germination. Aglycones content increased most at -20 °C, which increased about 24 times. The effect of thaw temperature and time indicated there were approximately 89 % glucosides forms converted to aglycones during freeze-thaw. Isoflavone conjugate-hydrolyzing β-glucosidase (ICHG) activity increased by 65.78 % (25 °C) and 59.14 % (48 h) with freeze-thaw. The cells of germinated soybeans were broken, promoting ICHG contact with glucosides and malonyl-glucosides. These results indicated that freeze-thaw greatly changed the content and profile of isoflavones, resulting in a sharp increase in the content of aglycones.
Keywords: Aglycones; Freezing; Germination; Glucosides; Thawing.
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