Milk proteins differentiation and competitive adsorption during spray-drying

Abstract

A non invasive method was developed to differentiate native whey proteins (NWI) and native micellar casein (NMC) at the surface of high protein milk powder. Surface analyses of the powders were performed by X-ray Photoelectron Spectroscopy (XPS). With this tool, it was impossible to differentiate casein and whey proteins by their C1s, O1s and N1s signature; the atomic percentage being similar. But, minerals at the surface of these proteins were significantly different. As a consequence, a calibration curve was obtained with known mixes of both proteins and was used for their differentiation.Competitive adsorption between casein and whey proteins during spray-drying was studied by a combination of different analytical methodologies (XPS, FTIR, zetasizer). The influence of the outlet air temperature on dairy proteins competition at the surface of the particle was investigated. For this purpose, three formulations were studied: 80/20, 50/50 and 20/80 (casein/whey proteins) and spray-dried at 80 and 130 °C (outlet air temperature). In formulations spray-dried at 80 °C, caseins were found overrepresented at the surface in comparison with the bulk composition. At 130 °C, the repartition between caseins and whey proteins was mostly the same at the surface and in the bulk. It was concluded that low outlet air temperatures allow the migration of surface-active components at the surface. As the spray-drying temperature increased, the surface may solidify and immobilize the proteins quickly, the surface being closer to the bulk composition.