Adsorption of isoflavones onto PVPP in the presence of a soy matrix

• Adsorption of isoflavones from okara onto PVPP was investigated as function of pH.
• Adsorption of aglycones and glycosides was described with partition coefficients.
• Precipitated protein in the water extract lowered the yield of adsorbed aglycones.
• Adsorption with the okara matrix present suggested concurrent extraction/adsorption.

The adsorption of isoflavones from an okara extract onto polyvinyl polypyrrolidone (PVPP) was studied for a pH ranging from 4 to 7.In general, the affinity of aglycones to PVPP was around 10 times higher than the affinity of the glycosides. Towards lower pH, the adsorption performance improved for the glycosides, especially for the malonyl-glucosides, but not for the aglycones. Towards neutral pH the affinity also increased, and showed the highest affinity for the total amount of isoflavones. Due to a large amount of protein present in the extract, some isoflavones were lost at lower pH due to the precipitation of protein, which led to losses of 3–25% in the protein fraction without any addition of PVPP.Moreover, PVPP was added to the crude starting material (i.e. okara), investigating the effect of the matrix on the adsorption and the possibility to combine the extraction and adsorption process. The isoflavone extraction was modelled using affinity constants of isoflavones to the matrix and the PVPP. The simulation showed that concurrent PVPP addition results in more extraction from the isoflavones from the matrix.