Multi-stage freeze concentration of fish protein hydrolysates: A CFD–experimental approach addressing viscosity and freezing point challenges

Freeze concentration is a promising technique for concentrating thermally sensitive liquids, particularly biomolecular solutions such as fish protein hydrolysates (FPH), while preserving functional and nutritional quality. However, its industrial application is constrained by two critical challenges: freezing point depression and viscosity increase, which hinder ice nucleation and separation. This study presents a multi-stage FC system specifically designed for FPH, integrating CFD simulations in ANSYS Fluent, MATLAB-based population balance modeling, and experimental validation. A final concentration of 36% (w/w solids) was achieved, with a corresponding viscosity of 188 mPa·s and a freezing point depression of −4.5 °C. To overcome ice propagation barriers, multiple crystallizers operating at staged refrigerant temperatures (−10 °C, −15 °C, −20 °C, and −25 °C) were employed. Simulation results showed strong agreement with experimental data, revealing that lower impeller rotational speeds significantly improved both ice fraction and mean crystal diameter, enhancing separation efficiency. These findings highlight the compounded effects of viscosity and freezing point depression on FC performance and establish a validated pathway for optimizing energy consumption and processing efficiency in high-viscosity bio-solutions.