ISOFLAVONE CONCENTRATION OF SOYBEAN IN CENTRAL EUROPE AS DETERMINED BY HPLC/UV ANALYSIS BEFORE AND AFTER ACID HYDROLYSIS

Isoflavones are phenolic compounds present in soybean and other legumes, which have attracted considerable attention because of various health effects associated with their bioactive properties. From twelve isoflavones known in soybean, nine are present in a glycoside form, whereas health effects are mainly attributed to the aglycones daidzein, genistein and glycitein. While most analytical methods focus either on total isoflavone content before hydrolysis or on isoflavone aglycones after hydrolysis, a two-step analytical procedure using HPLC separation and UV detection has been applied to detect both the isoflavone glycosides naturally present in soybean as well as their aglycones after acid hydrolysis. Five soybean genotypes of early maturity groups have been grown in the east of Austria in two climatically contrasting seasons, and seed samples were analysed for isoflavones. Total isoflavone concentrations of the soybean samples determined before and after hydrolysis ranged from 258-1137 mu g/g and from 140-748 mu g/g, respectively. For most isoflavones analysed, differences were statistically significant both for genotypes and growing seasons. The results suggest that the analytical procedure applied is useful both for selection of high isoflavone soybean genotypes as well as in quality control, particularly in view of isoflavone bioavailability.