Mechanical comparison of milk and whey protein isolate fouling deposits using indentation testings

Abstract Whey protein products have been previously used as a surrogate to mimic fouling and cleaning processes of dairy production. The basic idea builds on the fact that the main components of milk fouling are whey proteins and that the process from the solution to the fouling deposit is guided by similar chemical reactions. However, it remains unknown whether the resulting mechanical behaviour reflects that of milk deposits. Therefore, the objective of the present study is three-fold: In the first step, the mechanical characteristics of raw milk and whey protein fouling deposits were determined and compared with each other. In a second step, we aimed to quantify the amount of whey protein isolate needed to obtain a similar mechanical behaviour. For the determination of the time-dependent mechanical characteristics of milk and whey protein deposits, indentation and indentation relaxation experiments were performed. The outcomes of this study show that whey protein deposits, generated from a solution featuring a whey protein powder concentration of 0.1 g/l, lead to comparable mechanical characteristics to that of raw milk deposits. Furthermore, a significant influence of the milk deposit thickness on the mechanical behaviour was identified, resulting from the fouling generation process. Finally, a three-dimensional material modelling approach is suggested that can predict the time-dependent mechanical behaviour of milk fouling deposits.