Effect of casein/whey ratio on the thermal denaturation of whey proteins and subsequent fouling in a plate heat exchanger

Dairy fouling is a ubiquitous problem in food processing, however, the fouling mechanism is not fully understood and investigations arose mainly from experiments with model systems that contained only whey proteins, typically reconstituted from whey protein isolate powder (WPI). The effect of casein on fouling has been rarely considered despite it is the major component of milk proteins. To fill this gap, whey protein-based model fluids containing different casein concentrations and fixed content of added calcium were prepared, leading to various Casein/WPI mass ratios. The effect of Casein/WPI on beta-lactoglobulin (BLG) denaturation at molecular level and subsequent fouling behavior in the pilot-scale plate heat exchanger during pasteurization treatment was investigated. It was shown that Casein/WPI significantly affects the fouling behavior: at low Casein/WPI, fouling mass dropped dramatically until a minimum value was reached located at Casein/WPI of 0.2. While at higher Casein/WPI, fouling mass increased with elevated Casein/WPI. Element mapping of the fouling layer also reveals that different structures and fouling mechanisms occur depending on Casein/WPI ratio. Finally, it was established that contrary to WPI solutions, BLG thermal denaturation is poorly correlated to decrease/extent of fouling for casein protein-based solutions showing that the presence of casein deeply modifies mineral and protein interactions and fouling build-up.

Automated summary

The study revealed that the ratio of Casein/WPI in whey protein-based model fluids has a significant impact on fouling behavior. At low Casein/WPI ratios, fouling mass decreases dramatically, reaching a minimum value at a Casein/WPI ratio of 0.2, while at higher ratios, fouling mass increases. Different structures and fouling mechanisms were observed based on the Casein/WPI ratio, showing that the presence of casein alters mineral and protein interactions, affecting fouling build-up.