Effect of changes in ionic composition induced by different diafiltration media on deposited layer properties and separation efficiency in milk protein fractionation by microfiltration

Milk protein fractionation for casein/whey protein separation by microfiltration in diafiltration mode was investigated using washing waters differing in pH, calcium content and ionic strength. Properties of the deposit layer and process efficiency were assessed as functions of diafiltration progress and deposited layer structures were analysed. Results were compared with findings obtained in crossflow mode with a gradual change from milk to diafiltration medium. Deionised water as well as softened water induced a significant increase of deposited casein layer hydration, thereby increasing flux levels and separation efficiency. Dependent on water hardness, tap water was found to induce fewer changes to the deposit hydration and process performance indicating less change of casein micelles. These findings are consistent with the generic colloidal behaviour of casein micelles as previously determined through laboratory experiments. Therefore, waters with a certain degree of hardness could be recommended as the most suitable diafiltration medium not requiring pre-treatment.