Impact of formulation on reconstitution and flowability of spray-dried milk powders

The present study focuses on the impact of lipid content (1.5, 13.8, and 26 % (w/w)) and pretreatment of dairy concentrates (air incorporation by whipping prior to spray-drying) on the physicochemical and technofunctional characteristics of dairy powders. Spray-drying was performed according to the following conditions: 200 °C inlet air temperature and 85 °C outlet air temperature. Physicochemical properties (particle size distribution, shape factors, moisture content, water activity, and surface composition) of spray-dried powders were characterized in order to explain their reconstitution properties and flowability.The first part of the study revealed that changing the lipid content induced no significant difference of powder reconstitution. It was evidenced that median particle size of fatty powders was higher, thus counteracting the negative effect of powder surface hydrophobicity on its reconstitution behavior. Air incorporation in feed dairy concentrates did not significantly affect powder reconstitution properties, even if surface lipid content and median particle size were both decreased. Standard wettability and dispersibility tests were not relevant to evaluate the reconstitutability of investigated powders and all studied powders were classified as non-wettable and poorly dispersible.The second part of the study revealed that changing the lipid content induced a decrease in powder flowability both in unconfined conditions and under high normal stress. Powders were cohesive due to their low median particle size and their surface lipid coverage, nevertheless feed concentrates aeration induced an improvement of powder flowability by the decrease in surface lipid content. The bulk density (BD) and the compressed bulk density (CBD) both decreased with the lipid content, and the aeration of feed concentrates did not impact the BD but led to a decrease in CBD. Last, the compressibility increased with the lipid content and the aeration of feed concentrates, as the former increased particle cohesion and the latter induced the formation of smaller particles.