Circular Economy Approach for Whey Valorization: Coacervation of Proteins with Carboxymethylcellulose for Dairy Small- and Medium-Sized Enterprises

Abstract The valorization of whey, the main byproduct of cheese manufacture, is hindered for small and medium-sized dairy enterprises (SMEs) by the high cost of conventional separation technologies such as membrane filtration and chromatography. In this work, complex coacervation between whey proteins and carboxymethylcellulose (CMC) was scaled from 5 to 100 L to develop a simple, low-cost process for recovering a protein- and lipid-enriched product. Five commercial CMCs with molecular weights ranging from 18 to 780 kDa were first evaluated at laboratory scale. Intermediate-Mw CMC (400 kDa) provided the best balance between electrostatic complexation and sedimentation, removing 99% of the initial protein from the supernatant, as confirmed by residual protein quantification and turbidity. Using the selected CMC, the process was successfully scaled to 100 L in a conical-bottom tank with an off-centered 45° four-blade turbine. Geometric similarity (H/Dt = 2.0–2.5, Da/Dt = 0.26–0.33) was applied, achieving fully turbulent flow at both scales (Re = 3.56 × 104 and 1.41 × 105). Protein recovery reached 76%, with a 3.4-fold concentration of proteins and nearly complete fat recovery in the coacervate. The freeze-dried coacervate was readily redispersible up to 20% (w/v). Its ζ-potential shifted from near-zero at pH 3 to −40 mV above pH 6, reflecting the combined contribution of whey proteins and residual CMC. Thermal gelation of the coacervate (3.1% protein) was strongly pH-dependent: weak gels formed at acidic pH (G′ = 6–23 Pa), while strong, cohesive gels developed at alkaline pH (G′ = 325 Pa at pH 9). The lactose-rich supernatant showed reduced COD and BOD loads (12% and 28% reduction, respectively) and was successfully fermented by kefir grains without nutrient supplementation. This scalable, food-grade coacervation process offers an accessible alternative for dairy SMEs to transform whey from an environmental burden into a functional ingredient.