<p>We report on the physicochemical characteristics and protein adsorption properties of calcium phosphate suspensions obtained through heat-induced transformations of freshly precipitated brushite, prepared with varying precursors molar ratio. To this end, we developed a novel two-step thermal protocol to prepare heat-sterilized suspensions, which significantly improved the reproducibility of the materials’ physicochemical properties. The transformation mechanism of brushite was found to involve intermediate formation of octacalcium phosphate, which upon further heating and autoclaving converted into nanocrystalline apatite and monetite microcrystals. The relative amounts of these phases depended on the initial Ca/P molar ratio of the precursors. Protein adsorption by the resultant suspensions was relatively high, reaching up to approximately 90% adsorption efficiency—especially in the presence of Tris buffer at pH 6–7 and at higher Ca/P molar ratios in the supernatant. This high protein adsorption capacity is a key prerequisite for potential applications in protein delivery systems, such as vaccine adjuvants.</p> Graphical abstract <p></p>