Constituent fouling during heat treatment of milk: A review

Constituent fouling during thermal processing of milk is reviewed. Fouling occurs during continuous-flow thermal treatment, but the size and the type of fouling deposit strongly depend on both processing conditions (e.g., temperature, time, flow conditions) and product properties (e.g., composition, pH). Heat-induced destabilisation of proteins and heat-induced precipitation of calcium phosphate are the main drivers for component fouling during thermal processing. Whey proteins are included in fouling deposits at temperatures above their denaturation temperature, whereas caseins are included only at temperatures >100 °C. Calcium phosphate can be part of fouling deposits at temperatures >50 °C. Fat also contributes to fouling, but inclusion of fat is driven by interactions of proteins on the emulsion droplet surface. Component fouling of milk can be considered an extension of typical protein aggregation and salt precipitation mechanisms, where the deposit on the heating surface is considered as an additional, and often preferred, surface for interaction.