Environmental scanning electron microscopy as a novel tool to characterise in real-time the hydration of milk protein concentrates

The physical state of milk protein concentrate (MPC) powder particles during hydration is not well defined. Nanoparticle size plays a crucial role in the structural, flow and compositional properties of milk powders especially so when determining their subsequent hydration profiles. Particle size is an extremely useful indicator of quality and performance, particularly in the reconstitution of milk powders. Mainstream research has investigated milk powder hydration using bulk density methods. Using advanced bioimaging technologies the real-time hydration of milk powders can be observed at the level of the individual particle. Currently, there are no studies that have examined milk powder particles hydration using environmental scanning electron microscopy (ESEM). The aim of this study was to characterise the real-time hydration of MPC particles using ESEM. Low-(MPC40 and 50), medium-(MPC65 and 75) and high-(MPC85) protein content MPC powders manufactured by Teagasc, Moorepark, Fermoy were stored at 54 and 88 % relative humidity (RH) at 4 ºC. The hydration of the MPC powders were investigated under ESEM to examine the effects of storage temperature and RH. MPC40 and MPC50 which were stored at 54 and 88 % RH exhibited a weakening of the external framework leading to their subsequent collapse and in some cases full dissolution. MPC65 and MPC75 stored at 54 % RH revealed large breaks on the external skin of powder particles and MPC85 displayed little dissolution. MPC65, MPC75, and MPC85 stored at 88 % RH showed a graded disruption of the external skin of the powder particles. This study validates the use of ESEM as a novel tool to record dynamic in-situ hydration of milk powder particles.