The potential of crude okara for isoflavone production

•Opportunities to utilize okara as a source of isoflavones are shown.•Environmental friendly solvents (ethanol and water) are used as extraction solvents.•The crude okara can be used for extraction without prior drying.•50% Ethanol is sufficient for a high yield of isoflavones.•The highest purity/lowest protein concentration was found at 80% ethanol.

This study describes the extraction of isoflavones from crude okara, a by-product from soymilk production, using industrially relevant conditions. Ethanol and water were chosen as environmentally friendly and non-toxic solvents. A wide range of ethanol concentrations was tested (0–90% ethanol) for extraction at room temperature. It was shown that the extraction of isoflavones was possible from crude okara. This creates opportunities for a more attractive extraction process regarding industrial processing, as the energy-consuming step of drying could be omitted. The optimal concentration of isoflavones in the extract was reached with ethanol concentrations between 50% and 70%. Ethanol concentrations above 60% required an elevated liquid-to-solid ratio due to the high moisture content in okara. Increased ethanol concentrations lowered the protein content, which corresponded to an increase in purity. A high water content in the solvent resulted in co-extraction of a larger amount of other components.