Concentration of soybean isoflavones by nanofiltration and the effects of thermal treatments on the concentrate

An investigation was performed on the profile and the content of isoflavones in the concentrate of aqueous Defatted Soy Flour (DSF) extract obtained by nanofiltration. The effect of thermal treatments on these isoflavones was also evaluated according to a Central Composite Design (CCD 2k) with varying temperatures (70 to 90 °C) and times (15 to 45 min). Through nanofiltration it was possible to concentrate β-glucosides and malonyl glucosides (p < 0.05) in aqueous DSF extract but it was not possible to concentrate aglycones (p > 0.05). The thermal treatments applied on the concentrate showed that the malonyl glucosides were influenced by temperature (p < 0.05), while the β-glucosides were influenced not only by temperature but also by the time of interaction of the factors investigated (p < 0.05). Moreover, there was no alteration in the contents (p > 0.05) of aglycone or total isoflavones.