ABSTRACT
The specific isoflavone composition of nutritional supplements is commonly not-labeled, although the stated amounts are strongly dependent on the present isoflavone conjugates. Hence, 11 soy-based dietary supplements were characterized via a newly established ultra performance liquid chromatography (UPLC) method, on both their native conjugated isoflavone spectra, as well as on quantitative amounts derived as total aglycones after enzymatic hydrolysis utilizing Helix pomatia juice. Capitalizing on sub-2 microm particles, the established RP-UPLC technique facilitated efficient chromatographic separation of all 12 soy intrinsic isoflavone forms within 10 min. Derived native isoflavone profiles implied a certain variability, comprising conjugated forms, especially glycosides, as the predominant isoflavonic constituents throughout the majority of supplements, whereas only two samples indicated the more bioavailable free aglycones as prevailing compounds. Moreover, the robust quantification as total aglycones subsequent to enzymatic hydrolysis, unexceptionally yielded negative deviations referring to the labeled specifications, thus implying that stated amounts were typically calculated on basis of the high molecular isoflavone conjugates. Thus, especially in regard to better comparability, regulations concerning an uniform labeling basis are needed.
