Cleaning rate in the uniform cleaning stage for whey protein gel deposits

The removal of a thermally induced whey protein concentrate (WPC) gel layer from the inner surface of a stainless steel tube was determined continuously and non-invasively by a rapid UV spectrophotometric method. Based on mass transfer theory and polymer dissolution concepts, the constant cleaning rates in the uniform stage were predicted. The viscosity and solubility of WPC gels at different temperatures were measured and used in the modelling prediction. The deviation of the prediction from the experimental results indicates a possible change of protein fragment size with temperature. The investigation of the dissolution of WPC gel in 0.5 wt% NaOH solutions showed a break-up of disulphide bonds between protein molecules. The significant increase of the SH group content with increasing dissolution temperature was in agreement with the assumption that protein fragment size decreases with increasing temperature.