Fabrication of ferritin-casein phosphopeptides-calcium shell-core composite as a novel calcium delivery strategy

Plant ferritin endows a natural cage-like nanospace for carrying bioactive ingredients. By taking advantage of the calcium binding ability of casein phosphopeptide (CPP) and the cage like conformation of plant ferritin, the ferritin-CPP shell-core complex (FC) was fabricated by the reversible self-assembly character of ferritin induced by a pH 2.0/7.0 transition strategy. The FC-calcium composite (FCC) was further fabricated by binding of FC with calcium ions. When a same amount of calcium was loaded, the calcium binding capacity of FCC was 28.13±1.65%, which was significantly higher than that of ferritin and CPP alone. Fluorescence and Fourier transform-infrared analysis indicated that the CPP encapsulation and the calcium binding in FCC influenced the ferritin structure. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) results showed that the spherical morphology and the 12 nm-diameter size were sustained in FC and FCC. Moreover, FCC as a transport carrier could increase the precipitation time of calcium phosphate, and the encapsulated calcium could be released in a more sustained manner as compared with that of ferritin and CPP under the simulated in vitro gastrointestinal conditions. This study presents a novel calcium delivery strategy based on ferritin cage and CPP, which will improve the applicability of ferritin and CPP and enhance the bioavailability of calcium ions.