Membrane Cleaning Protocols for Liquid Polydisperse Milk-Protein Systems with Lactulose

The growing global demand for prebiotics, particularly purified lactulose, is constrained by the difficulties in isolating it from culture working solutions. As a rule, such a solution is a mix of enzymes and whey permeates with a wide variability of physicochemical properties, which complicates the separation process. This article introduces a new method for membrane separation of lactulose-protein culture solutions. By studying the physicochemical properties of the initial polydisperse milk-protein system, the authors determined the effect of micro- and ultrafiltration on permeate fluxes. The data obtained made it possible to develop an optimal purification protocol. The research involved standard equipment, materials, and experimental data processing methods. The main model object of membrane separation was comparable in dry matter content to wastewater from dairy processing plants. It was prepared using a water-based mix of enzymes (e.g., K. lactis Y-1339 + S. thermophilus BK-Uglich-TV), a standard dry cheese whey permeate, and an anionic surfactant. The samples of the liquid polydisperse milk-protein system differed significantly in particle size distribution but were similar in terms of total protein and dry matter mass fractions. The permeability of micro- and ultrafiltration membranes was determined by the processing time, total protein mass fraction, and particle size distribution of the dispersed phase. The experiment proves that a high-quality purification must include a preliminary fine filtration or microfiltration followed by ultrafiltration.