Role of β-lactoglobulin in the fouling of stainless steel surfaces by heated milk

Fouling occurred in sudden expansion (SE) test pieces in holding tubes downstream of a direct steam injection (DSI) heater. The fouling deposit contained high levels of protein, mainly β-lactoglobulin, and fat. Fouling during a run was monitored using heat flux sensors to determine the local fouling rate. The overall fouling rate was determined after a run from the weight of deposit and the overall time that fouling occurred during a run. Local and overall fouling rates were correlated. Fouling was high in SEs close to the DSI heater and diminished in SEs placed further downstream. The fouling rate was correlated with the level of native β-lactoglobulin remaining at the position of the SE. It is proposed that the fouling was due to a reactive intermediate of β-lactoglobulin that interacted with deposits on the SE surface. The considerable variation in fouling rates between runs suggests other environmental factors are also important.