Calcium carbonate nanoparticles were synthesized by reactive precipitation of sodium carbonate and calcium chloride solutions (0.10 M) using a high pressure jet homogenizer in the presence of sodium caseinate as stabilizer. Based on mixing theory, an estimation of mixing time (t(mix)) of salt solutions as a function of pressure drop was calculated considering the homogenizer as a T-mixer followed by a homogenization chamber for particle aggregate disruption. Pressure losses higher than 20 MPa were required to produce nanoparticles (z-average = 100 nm). The effect of total pressure drop (20-36 MPa), pH (6.0-10.0), temperature (5.0-40.0 degrees C) and protein concentration (1.0-3.0%) on nanoparticle formation were evaluated using a 3(2) and a 3(3) factorial design. Temperature and protein concentration showed to be the most relevant factors of nanoparticle formation. Transmission electron microscopy images indicate that calcium carbonate nanoparticles produced in the jet homogenizer have a multiple core structure, with primary particles (c.a. 6 nm in diameter) immersed in a protein matrix that corresponds to 35% of the total nanoparticle mass. The calcium carbonate multiple core nanoparticles could find applications in food, pharmaceutical and chemical industry considering their innocuity and protein functionalization. (C) 2011 Elsevier B.V. All rights reserved.