Toward a circular economy in the tofu production: Valorization of tofu whey in functional ingredients and coagulant agents through membrane processes

Tofu whey, a by-product of tofu production, presents an opportunity for valorization within a circular economy framework. This study compares two membrane-based processes for the recovery and utilization of residual proteins and other valuable compounds from tofu whey: 14× tofu whey concentration using nanofiltration (NF) and demineralization of the resulting permeate via electrodialysis (ED) (Process 1) versus 14× concentration through NF operated in diafiltration mode (NF/DF), followed by reverse osmosis (RO) to reconcentrate the diluted permeate and demineralization of the RO retentate by ED (Process 2). Process 2 demonstrated superior performances, with a protein recovery yield of 72 ± 9 %, compared to 55 ± 6 % for Process 1. Functional properties, including solubility, foaming properties and emulsifying properties were evaluated for tofu whey and both retentates. While tofu whey displayed comparable functionality to some commercial soy protein isolates (SPIs), the retentates from both processes demonstrated superior functional properties. Notably, the NF/DF retentate from Process 2, due to its higher protein purity and improved functional attributes, is particularly well-suited for applications as a functional protein ingredient or in high-protein beverages. Beyond protein recovery, other by product also demonstrated valorization potential. The sugar-rich permeate, containing prebiotic oligosaccharides such as stachyose and raffinose, may serve as a substrate for fermentation or as a natural sweetener. The ED recovery solution, enriched in minerals, has potential for reuse in tofu production as coagulants, and water recovered from RO can be recycled within the process at the DF step. Overall, this study shows a circular economy approach for turning tofu whey into valuable ingredients. • NF performed in DF mode enabled a superior protein purification from tofu whey. • The functional properties of the proteins are similar or superior to commercial SPIs. • Every recovered fraction has a potential for valorization.