FT-IR Method for the Quantification of Isoflavonol Glycosides in Nutritional Supplements of Soy (Glycine max (L.) Merr.)

Abstract

Due to increasing health consciousness, a lot of food supplements are sold and used. Dietary supplements of Glycine max (L.) MERR. are used as an alternative treatment for menopausal complaints such as hot flashes. Thereby, the effective soy compounds are the isoflavones daidzin, genistin, and glycitin. However, only the total soy extract content of the nutritional supplements is indicated. The aim of this study is to introduce a fast, efficient, and economic Fourier transformation infrared (FT-IR) spectroscopy method to quantify the active ingredients in the complex matrix of soy-based supplements. Five different nutritional supplements of Glycine max (L.) MERR. were purchased from a German pharmacy and were extracted with 80% aqueous methanol. A high-performance liquid chromatography (HPLC) method was used for the separation. The samples were concentrated and measured with infrared spectroscopy. An FT-IR method was established to quantify the active ingredients in the complex matrix of soy-based nutritional supplements. The partial least-squares algorithm was used to develop the method, which enabled the estimation of the content of particular isoflavones (daidzin R2 = 0.86, glycitin R2 = 0.94, genistin R2 = 0.96) and the quantification of the total isoflavone content (R2 = 0.92) despite peak overlap in the infrared (IR) spectra. The method for the quantification of the isoflavonol glycosides is precise with the standard error of prediction being 13.54%.

A brief history and spectroscopic analysis of soy isoflavones

“…The IR spectrum of soy isoflavones showed absorption bands for hydroxyl (3365 cm -1 ) and conjugated carbonyl (1694 cm -1 ) functional groups (Boonyaketgoson et al, 2015). On the contrary, it has been reported that the IR spectra of soy isoflavones were obtained in the wavenumber range of 2000-600 cm -1 (Iizuka and Aishima, 1999;Jose et al, 1974;Krähmer et al, 2013;Mulsow et al, 2015). The IR spectroscopy of soy isoflavones revealed that the quantitative values of pretreated samples were very similar to the results of the HPLC (Mulsow et al, 2015).…”

“…On the contrary, it has been reported that the IR spectra of soy isoflavones were obtained in the wavenumber range of 2000-600 cm -1 (Iizuka and Aishima, 1999;Jose et al, 1974;Krähmer et al, 2013;Mulsow et al, 2015). The IR spectroscopy of soy isoflavones revealed that the quantitative values of pretreated samples were very similar to the results of the HPLC (Mulsow et al, 2015). In the case of foods, however, the pre-treatment of the sample or the post-processing of the data is necessary for IR spectroscopy because of the water (Iizuka and Aishima, 1999).…”

Analysis of Isoflavones in Foods

“…The latter included the addition of 70% methanol followed by the use of sonication at 0 °C for 20 min. A procedure similar to that proposed by Shim and others () was used by Mulsow and others () for the extraction of isoflavonol glycosides in soy nutritional supplements. Aqueous acetonitrile containing a small amount of dimethylsulfoxide (Collison ) has also been used in an interlaboratory study for the determination of total soy isoflavones in dietary supplements, dietary supplement ingredients, and soy foods.…”

Development and Validation for Free Aglycones Daidzein and Genistein in Soybeans (Glycine Max (L.) Merr.) Using Rp HPLC Method

“…Several analytical methods have been used for analysis of daidzein and genistein, namely high-performance liquid chromatography (HPLC) [10][11][12], Raman spectroscopy [13], FTIR spectroscopy and [14] polarimetry [15]. The most widely used analytical technique is reversed phase HPLC using C18 column with the mobile phase of acetonitrile, methanol [10,11,16].…”