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Spray-dried milk powders are characterized by an underrepresentation of hydrophilic compounds on the particle surface compared to the bulk, which renders reconstitution unfavourable. To overcome this issue, in the present study we instigated the coating of whole milk powder with two types of micronized lactose: crystalline and amorphous. We demonstrate that deposition of micronized lactose on the surface of whole milk powder leads to an increase in the reconstitution rate at 21 °C, correlated with a decrease in the apparent contact angle of the material. We also show that the physical solid state of micronized lactose is an important factor influencing the reconstitution performance of coated whole milk powder; If micronized lactose is amorphous, increasing the coating concentration beyond a certain point has little or no further effect on the reconstitution kinetics, which could be explained by viscosity build-up effects that hamper capillary penetration and sinking. [Display omitted] • Dry coating of whole milk powder with micronized lactose (crystalline/amorphous) • Enhancement of powder wettability and reconstitution at 21 °C • Powder sinking is influenced by the physical solid state of the coating material [ABSTRACT FROM AUTHOR]

[Display omitted] • At 40 °C/400 rpm, amorphous micronized lactose improves reconstitution, crystalline has the opposite effect. • Dissolution enthalpy of the coating material could influence the surface fat properties. • No differences at 800 rpm or if whole milk powder is agglomerated. Reconstitution of dairy powders is strongly influenced by the presence and physical state of fat on the particle surface. The present study investigates the effect of a micronized lactose coating on the physical state of the fat and the reconstitution kinetics of whole milk powder at four different temperatures (4/21/40/60 °C) and two stirring rates (400/800 rpm). For this purpose, two types of micronized lactose were used as coating materials: crystalline and amorphous. At 4 °C and 21 °C, the coated powders sink and are reconstituted faster than pure whole milk powder, regardless of the stirring rate applied. At 40/60 °C and 400 rpm, although the amorphous micronized lactose coating leads to a significant decrease in the reconstitution time, the crystalline coating has the opposite effect (or no effect). This discrepancy is related to the large differences in terms of dissolution enthalpy between the two micronized lactose physical states. It is posited that the dissolution of the coating material causes a temperature shift at the powder-water interface which could hamper the complete melting of surface fat and influence its viscosity, thereby affecting wetting and sinking. These differences are overcome at a high stirring rate (800 rpm) or if agglomerated whole milk powder is used as the host material. [ABSTRACT FROM AUTHOR]