Interactions of casein and carrageenan with whey during pasteurization and their effects on protein deposition

Despite significant research to date to understand dairy fouling, most efforts have focused on milk ingredients, especially whey protein. In contrast, little is known about the effects of other milk proteins like casein and non-milk ingredients such as carrageenan gum. Therefore, the fouling mechanisms of complex dairy products are still elusive. In this study, different model dairy solutions were prepared with whey protein isolate (WPI; 2 wt%), casein (0.5 wt%) and κ-carrageenan (0.03 wt%), and their fouling behaviors during high-temperature-short-time pasteurization (~73 ºC) were characterized under well-controlled flow. The addition of casein into WPI solution significantly increased its fouling tendency because casein reduced the thermal stability of whey, but the deposits formed were more porous with apparent fractures. As evidenced by fluorescence and Raman spectroscopy analyses on the changes in protein structures and increased exposure of tryptophan residues, the presence of casein was confirmed to facilitate the denaturation of β-lactoglobulin. Adding κ-carrageenan increased the fouling of WPI solution with formation of more compact deposit. This work sheds light on the interactions of milk proteins with polysaccharides under thermal processing conditions and is expected to provide the dairy industry with knowledge of designing dairy formulation with reduced fouling tendency.