Effect of Plate-and-Frame Filtration Temperature on the Functionality of Milk Protein Concentrate Powder

Maintaining functional integrity during ultrafiltration-based concentration of milk protein concentrate (MPC) is as critical as achieving high solids in the retentate. Previous studies demonstrated that ultrafiltration in plate-and-frame filtration (PF) modules can effectively concentrate MPC derived from spiral-wound ultrafiltration (UF) of skim milk, particularly at elevated temperatures. This study compares the functionality of powdered MPCs produced via UF and PF systems. Skim milk retentate from UF containing 20% total solids and approximately 80% protein on dry basis (feed) was processed using PF modules equipped with flat-sheet membranes across 3 replicates. Three PF treatments were applied: PF22 at 22°C, PF50MS at 50°C targeting medium solids, and PF50HS at 50°C targeting high solids. Filtration for PF22 and PF50HS continued until transmembrane pressure reached 900 kPa, while PF50MS was terminated upon achieving ∼30% solids. Retentates from UF, PF22, PF50MS, and PF50HS were spray-dried and evaluated for rheological and functional properties. All reconstituted MPC powders exhibited pseudoplastic behavior, best described by the Herschel-Bulkley model. Functional assessments revealed that rennet coagulation time increased with PF temperature, necessitating the addition of ∼0.25% CaCl₂ to achieve timely coagulation. Elevated PF temperatures negatively affected other functional attributes, including increased wetting time, reduced solubility, and shortened heat coagulation time-most notably in PF50HS compared with PF22 and UF. Conversely, high-temperature PF enhanced emulsion stability without altering emulsion formation. All PF treatments improved foaming capacity while maintaining comparable foaming stability to UF. A slight reduction in whey protein content and increased protein denaturation was observed at higher PF temperatures. These findings underscore the importance of temperature optimization in preserving the functional properties of MPC during PF concentration.