Microporous materials of controlled pore size were prepared by means of a three-step process involving in situ hydrochemical preparation of a hydroxyapatite-sodium caseinate (HAp-Cas) composite material into a Cas-stabilized oil-in-water emulsion, subsequent concentration and drying of the composite-emulsion, and removal of the oil by means of supercritical carbon dioxide extraction. The resulting composite materials were found to contain micron-sized pores in the space previously occupied by the oil droplets. In order to elucidate the structure of the resulting porous product, its Cas-HAp composition was studied in the corresponding nonporous composite material. In nonporous samples, a protein assay by means of visible spectroscopy suggested equilibrium between the Cas that was trapped in the composite structure and the Cas that remained in solution after precipitation. This observation was confirmed by separate thermogravimetric analysis and Fourier transform IR spectroscopy measurements.