DETERMINATION OF SOY ISOFLAVONES IN FOOD SUPPLEMENTS BY 1H-qNMR

Isoflavones are a class of compounds with estrogenic activity and they are found in small amounts in a number of legumes, grains, and vegetables, but soybeans are by far the most concentrated source of isoflavones in the human diet. Soy products that are gaining popularity in Western countries include soy-based meat substitutes, soy milk, soy cheese, and yogurt and many different food supplements, in which, soy extracts may be present alone or in association with others natural compounds. Soy isoflavone extracts are available as dietary supplements without a prescription in the majority of countries and also in Italy. These products are not usually standardized, and the amounts of isoflavones they provide may vary considerably. Moreover, quality control may be an issue with some of these products [1]. When isoflavone supplements were tested for their isoflavone content, the isoflavone content in the product differed by more than 10% from the amount claimed on the label in approximately 50% of the products tested [2]. For this reason 1H NMR spectra of different methanolic extracts of soy-based food supplements were recorded using a Bruker FT-NMR AVANCE III HD 600 MHz spectrometer. It was possible to identify signals belonging to the soy isoflavones in the aromatic zone (from 6.5 to 8.5 ppm). Genistein, daidzein and glycitein signals were assigned also using 13C, JRes and heteronuclear experiments such as HSQC and HMQC. The identified compounds were tentatively quantified using ERETIC 2 method. The obtained results further demonstrate the potential of the NMR technique in food chemistry.