Isoflavones food analyses

Wang J and Sporns P. 2000b. MALDI-TOF MS analysis of isoflavones in soy products. J Agric Food Chem... 

Barnes, S., Kirk, M., and Coward, L., Isoflavones and their conjugates in soy foods extraction conditions and analysis by HPLC-mass spectrometry, J. Agric. Food Chem., 42, 2466, 1994. 

Analysis of Isoflavones in Soy Foods Basic Protocol 1 Solvent Extraction of Isoflavones in Their Natural Forms 11.6.1... 

Soybeans and soybean products contain high levels of protein, carbohydrates, and lipids (Table 11.6.1). As minor components of complex mixtures, isoflavones must first be separated from the bulk of the matrix constituents prior to analysis. Efficient extraction methods for isoflavones should account for their diverse structures, chemical properties, and the food matrix of which they are constituents. This unit describes a practical way of extracting isoflavones from soybean products in their natural forms using readily available solvents and laboratory equipment. 

Quantification. For accurate quantification, a standard curve of peak area versus concentration should be constructed for each standard using the same chromatographic conditions (e.g., wavelength and solvent) as for the samples under analysis. The concentration range of standard curves should be determined according to both the isoflavone level of soy food samples and dilution factors during sample preparation such that the UV absorbance of the injected sample is within a range of 0 to 1. The appropriate standard curve can then be used to calculate the quantity of isoflavones represented by each HPLC peak in the sample. 

Griffth, A.P. and Collison, M.W. 2001. Improved methods for the extraction and analysis of isoflavones from soy-containing foods and nutritional supplements by reversed-phase high-performance liquid chromatography and liquid chromatography-mass spectrometry. J. Chromatog. A 913 397-413. 

A systematic investigation in extraction and analysis of isoflavones from soy-containing foods and nutritional supplements. 

Traditionally HPLC methods were used for isoflavone analysis from foods [Wang et al., 1990], and gas chromatography/mass spectrometry (GC/MS) to determine isoflavones and their metabolites in human biological fluids including urine [Adlercreutz et al., 1991 Kelly et al., 1993], plasma [Adlercreutz et al., 1993], and feces [Adlercreutz et al., 1995 Kurzer et al., 1995]. HPLC with photodiode array (PDA) detection was introduced in 1994 to measure these analytes in human urine [Franke and Custer, 1994 Xu et al., 1994]. Compared to GC/MS, HPLC methods require fewer steps for sample preparation and analysis and demand less technician time and less expensive instrumentation. 

Table 3.6 Methodological Overview of Isoflavone Analysis from Foods and Biological Samples...

In a study of retail soy foods, Murphy et al. (1999) optimized extraction of isoflavones and found that the amount of water included in the mixture of acetoni-trile-0.1 N HCl-water affected the yield of isoflavones in various foods matrices. Two grams of samples were extracted with 10 ml acetonitrile, 2 ml of 0.1 N HC1 and an amount of water. The optimal amount of water ranged from 5 to 10 ml, depending upon the type of food matrix. The standard deviation of the optimized extractions ranged from 0.6% to 4.8% for total daidzein and 0.2-3.5% for genistein analysis. HPLC with a C18 column was used to separate the isoflavones, which were... 

Many factors contribute to the variability of isoflavone contents in foods, including raw material characteristics, extraction and analysis procedures. Soybeans are affected... 

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