Cleaning-in-place of whey protein fouling deposits: Mechanisms controlling cleaning

The processes involved in alkali-based cleaning-in-place of whey protein deposits were investigated using cleaning solutions of 0.5wt% NaOH over a range of surface temperatures (20-80 degrees C) and flow rates (Re = 500-5000). Cleaning was quantified by measuring both mass removal and the change in the thermal resistance of the deposits. The results confirmed that cleaning involved three stages, namely deposit swelling, uniform erosion and a final decay phase. The evolution of structure in the protein network on contacting NaOH was elucidated with SEM and surface fixation techniques on samples generated by a short contact time apparatus. The effects of temperature and flow rate on the cleaning rate changed between the uniform and breakdown stage. The protein removal rate in the uniform stage was strongly dependent on conditions at the deposit/solution interface, while that in the decay phase was more sensitive to flow rate (i.e. surface shear stress). Reaction and diffusion of protein within the swollen deposit matrix appear to control the uniform cleaning rate. Simultaneous measurements of thermal resistance and protein removal did not show a simple correlation and suggest that existing models for cleaning require further development.