Phosphate and calcium effects on the heat-denaturation of whey proteins and on the fouling mass deposited onto the surface of a heat exchanger surface.
Résumé
Fouling of plate heat exchanger surfaces during dairy processing promotes a negative impact on the industrial operation efficiency. The most important compounds of the deposits on the exchange surface are minerals (mainly calcium and phosphate) and also heat-sensitive whey proteins, β-Lactoglobulin being considered as a precursor in the formation of proteinaceous fouling deposits. Today the molecular interactions between minerals and whey proteins in the mechanism of deposit build-up are not well understood. In this study, the kinetics of β-Lactoglobulin denaturation, the structure of the particles formed as well as the amount of deposit onto the surface of a plate heat exchanger were assessed by heating model fouling fluids (whey protein isolates at 0.5 wt. %, containing various amounts of calcium and phosphate) at a temperature ranging from 75 to 95ºC. Whatever the concentration of calcium and phosphate, the denaturation kinetics of β-Lactoglobulin was best fitted using an overall reaction order equal to n=1.5. The β-Lactoglobulin denaturation rate constant was maximum in solution at a higher calcium concentration and was lowered at an increased concentration of phosphate. Additionally, for ionic conditions leading to a similar heat-denaturation rate constant of β-Lactoglobulin, the size of the formed particles was smaller in fouling fluids containing a higher amount of phosphate below around 90°C. This could be well analyzed regarding the amount and structure of the fouling deposit.