RESUMEN
Objective To determine the contents of isoflavones in the form of aglycones (daidzein, genistein) as well as respective β-glycosides (daidzin, genistin), and their presence in UHT and fresh soymilk available in Amphur Muang, Chiang Mai, Thailand. Methods Ten samples of ultra high temparature (UHT) processed soymilk and 20 samples of fresh soymilk were randomly purchased from different zones. Isoflavone contents in each sample were determined by high performance liquid chromatography. Results Isoflavone contents in both soy beverages ranged from approximately 10-70 mg/serving, and β-glycosides dominated. The median concentration of aglycones in fresh soymilk was significantly greater than that in UHT soymilk, whereas, the median values of β-glycoside concentrations, total isoflavone concentrations and the total isoflavones per serving (mg) in UHT soymilk were significantly greater than those in fresh soymilk. Nonetheless, the median value of maximal absorbable isoflavones per serving (in the unit of μmol) did not significantly differ between the two soy beverages. Conclusion Isoflavone contents in both soy beverages varied substantially. Although the proportions and concentrations of aglycones and β-glycosides as well as the total isoflavones per serving (mg) were significantly different between both soy beverages, the maximal absorbable isoflavones per serving (μmol) did not significantly differ. Chiang Mai Med Bull 2004;43(4):151-161.