Sustainable recovery of residual proteins from tofu whey by coupling nanofiltration with electromembrane processes and functional properties of resulting protein fractions

In this study, a process was evaluated for the recovery of residual proteins from tofu whey. This process involved the coupling of a pre-concentration of tofu whey by nanofiltration (NF) at a 9× volume concentration factor, with demineralization by electrodialysis (ED), followed by electro-acidification through electrodialysis with bipolar membranes (EDBM) and centrifugation. The process resulted in a protein recovery of 25.1% in the final precipitate fraction. Molecular weight analysis showed that most proteins in tofu whey, retentate, precipitate and supernatant were under 1000 Da, with similar profiles suggesting no specific protein isolation in the precipitate. In addition, the functional properties of the fractions at each step of the process (Tofu whey, NF retentate, precipitate and supernatant) were assessed and compared with three commercial soy protein isolates (SPIs). For the first time, the functional properties of tofu whey proteins recovered by the NF + ED + EDBM process were systematically studied. Surprisingly, despite the residual proteins in tofu whey fractions having smaller molecular weights than the 7S and 11S proteins in SPIs, their functionalities were comparable, and in some cases, superior. The final supernatant and NF retentate exhibited better solubility, foaming properties, and emulsifying capacity than the SPIs, while the tofu whey and final precipitate demonstrated similar functional properties. These results suggest that all fractions could serve as valuable functional ingredients in food formulations, contributing to the valorization of tofu whey within a circular economy framework. However, it appeared that the EDBM step would not be necessary to valorize tofu whey in a more economical way.