Fundamental characterisation of caseins harvested by dissolved air flotation from dairy wastewater and comparison with skim milk powder

Disposal of milk protein-containing wastewater from the milk industry is of considerable environmental concern. Solid material, including caseins, can be harvested in large quantities from dairy factory wastewater using dissolved air flotation (DAF). DAF-casein is an under-utilised waste product that has potential for added-value products. In this study, the fundamental properties of DAF-casein were compared with skim milk and skim milk powder. The gel electrophoresis protein migration pattern of DAF-casein had a casein profile similar to that of skim milk powder. DAF-caseins differed from skim milk powder in their hydrophobic properties when analysed by reversed phase-high performance liquid chromatography and partitioning in chloroform-methanol. Casein prepared from skim milk by acid coagulation exhibited hydrophobic properties similar to those of DAF-casein, but differed in rheological properties. This indicates that dairy industry cleaning-in-place procedures, combined with DAF processing of the wastewater to generate DAF-casein, cause changes in protein composition and hydrophobic properties.