Glycomacropeptide (GMP) shows potential for enhancing the rehydration properties of high-protein dairy powders due to its hydrophilic nature. This study involved formulating micellar casein concentrate (MCC) solutions (8.6% final protein content) with 0, 10, and 20% GMP as a percentage of total protein, and investigated the physicochemical and rehydration properties of the resultant freeze-dried powders (P-MCC-0G, P-MCC-10G, and P-MCC-20G, respectively). The surface charges of caseins in the control MCC and 10 or 20% GMP blended solutions were −25.8, −29.6, and −31.5 mV, respectively. Tablets prepared from P-MCC-10G or P-MCC-20G powders displayed enhanced wettability with contact angle values of 80.6° and 79.5°, respectively, compared with 85.5° for P-MCC-0G. Moreover, blending of GMP with MCC resulted in faster disintegration of powder particles during rehydration (i.e., dispersibility) compared to P-MCC-0G. Faster and more extensive release of caseins from powder particles into solution was evident with the increasing proportion of GMP, with the majority of GMP released within the first 15 min of rehydration. The results of this study will contribute to further development of formulation science for achieving enhanced solubility characteristics of high-protein dairy powder ingredients, such as MCC.

The rehydration properties of original whey protein isolate (WPI_C) powder and spray-dried WPI prepared from either unheated (WPI_UH) or nanoparticulated WPI solutions were investigated. Nanoparticulation of whey proteins was achieved by subjecting reconstituted WPI_C solutions (10% protein, w/w, pH 7.0) to heat treatment at 90 °C for 30 s with no added calcium (WPI_H) or with 2.5 mM added calcium (WPI_HCa). Powder surface nanostructure and elemental composition were investigated using atomic force microscopy and X-ray photoelectron spectroscopy, followed by dynamic visualisation of wetting and dissolution characteristics using environmental scanning electron microscopy. The surface of powder particles for both WPI_UH and WPI_C samples generally appeared smooth, while WPI_H and WPI_HCa displayed micro-wrinkles with more significant deposition of nitrogen and calcium elements. WPI_H and WPI_HCa exhibited lower wettability and solubility performance than WPI_UH and WPI_C during microscopic observation. This study demonstrated that heat-induced aggregation of whey proteins, in the presence or absence of added calcium, before drying increases aggregate size, alters the powder surface properties, consequently impairing their wetting characteristics. This study also developed a fundamental understanding of WPI powder obtained from nanoparticulated whey proteins, which could be applied for the development of functional whey-based ingredients in food formulations, such as nanospacers to modulate protein–protein interactions in dairy concentrates.