Effects of supplementing sodium caseinate on rehydration properties of spray-dried milk protein isolates

Abstract

Poor rehydration properties of spray-dried milk protein isolate (MPI) are one of the major challenges for its applications. In this study, sodium caseinate (NaCas) was added in the MPI dispersions at a total solid concentration of 8 g/100 mL and NaCas:MPI mass ratios of 0:1, 1:9, 3:7, 1:1, and 1:0 for spray-drying. The addition of NaCas improved the static hydration properties of the powders, with the 1:1 treatment being similar to NaCas showing homogeneous dispersions within 60 min. NaCas also improved the dynamic hydration properties of MPI according to the changes of Z-average diameter, protein solubility, total solids solubility, and morphology during stirring for up to 240 min, and the 1:1 treatment was dissolved the fastest, within 10 min. The sodium dodecyl sulfate–polyacrylamide gel electrophoresis and microscopy results showed that the hydration rate was limited by surface micellar casein that was inter-linked and formed a crust layer. The scanning electron microscopy results further indicated that the added NaCas reduced the connection of casein micelles on powder particle surface and therefore accelerated the dissolution of the surface layer and release of interior matters. This study may be significant to improve the hydration and therefore applications of spray-dried milk protein ingredients.