Isolation of isoflavones

Hessler, P.E., Larsen, P.E., Constantinou, A.I., Schram, K.H., and Weber, J.M. 1997. Isolation of isoflavones from soy-based fermentations of the erythromycin-producing bacterium Saccharopolyspora erythraea. Applied Microbiol. Biotech, 47 398 404. 

Isol. from Iris germanica, /. unguicularis, Monopteryx inpae and from cultures of Streptomyces sp. Shows antihypertensive props. Mp 231°. All isolations of isoflavones from microorganisms are considered suspect. 4, 6-Di-Me ether, 7-O-P-D-glucopyranoside [37744-61-9]. Iristectorin A... 

Isol. from cultures of Aspergillus niger. DOPA decarboxylase inhibitor. Brownish cryst. (MeOH/CgH ). Mp 252° dec. All isolations of isoflavones from microorganisms are considered dubious. 

Metab. of Aspergillus niger. All isolations of isoflavones from microorganisms are considered suspect. 

In order to produce soy protein, soybeans are first dehulled, flaked, and defatted to make white flakes . Soy protein concentrates are obtained by removing a portion of the carbohydrates from defatted and dehulled soybeans. Alcohol extraction is the method most commonly used to manufacture soy protein concentrates even though it results in the loss of isoflavones. Soy protein concentrates retain most of the fiber in the original soybean and must contain at least 65% protein on a moisture-free basis to meet quality standards. The most concentrated source of soy protein is soy protein isolates (or isolated soy protein, ISP), which is required to be at least 90% protein on a moisture-free basis. It is heat-treated during processing to insure inactivation of trypsin inhibitors. Most isolated soy protein is manufactured by water extraction from defatted and dehulled soybeans and it retains the natural isoflavones. 

HUR H G, LAY J o Jr, BEGER R D, FREEMAN J p and RAFii F (2000) Isolation of human intestinal bacteria metabolizing the natural isoflavone glycosides daidzin and genistin. Arch Microbiol. 174 (6) 422-8. 

Eldridge (1982a,b) reported analysis of soybean and soy products using HPLC with an external standard method. They found 80% ethanol extraction for 4 hr was suitable for extraction of isoflavones from soybean, soy protein concentrate and protein isolate. They also found that daidzin and genistin accounted for 50-75% of the total isoflavones. Eldridge and Kwolek (1983) reported analysis using selected external standards and n-butyrophenone as an internal standard. 

Johns et al. (2000) reported an anion exchange technology using Amberlite or Dowex or other resins to isolate phytoestrogens from plant protein materials. Carbonate or bicarbonate was used as a counterion to avoid chlorides or alkali in the final product. Protein slurry was passed through the column at pH 6-8. The bound isoflavones were released with alcohols, organic solvents or acid or base solution. The protein isolate produced was essentially free of isoflavones. 

Eldridge, A.C. 1982a. Determination of isoflavones in soybean flours, protein concentrate and isolates. J. Agric. Food Chem. 30 353-355. 

In most instances, the above-mentioned trials used isolated soy protein or soy milk with known content of isoflavones. The modest impact of soy consumption on thyroid laboratory parameters was also confirmed by the most recent crossover study (Dillingham et al., 2007) on healthy young men, which also correlated the data of thyroid hormones with the urinary excretion of both major isoflavones. It is to be noted that, with only the latter exception, the effect on thyroid parameters was not the primary health outcome of these investigations. 

Lopes Barbosa, A.C., Lajolo, F.M., Genovese, M.I. Influence of temperature, pH and ionic strength on the production of isoflavone-rich soy protein isolates. Food Chem. 98(4), 757-766 (2006)... 

---