Native phosphocaseinate (NPC) is an innovative dairy based ingredient. However, its storage induced lipids released onto the surface, which has repercussions on powder functional properties. In this study we have investigated the effect of storage on surface composition, water sorption properties and powder microstructure. The combination of these analytical methods has been used to enhance the understanding of powder lipids released during storage. First, lipids were found to accumulate preferentially at the surface of the particle even when they were stored at 20 degrees C. Powder microstructure after storage showed the presence of pores, indicating a possible way of lipids released. Sorption studies revealed that the monolayer moisture capacity (X(m)) decreased during storage is mainly due to the formation of a lipid barrier on the powder surface. Finally, we have confirmed observations made by other researchers on the localization of milk components during spray drying and we have added new knowledge during storage. (C) 2009 Elsevier Ltd. All rights reserved.