Dual Decoration of Ferritin Nanocages by Caffeic Acid and Betanin with Covalent and Noncovalent Approaches: Structure and Stability Analyses.

Ferritin is a cage-like protein with modifiable outer and inner surfaces. To functionalize ferritin with preferable carrier applications, caffeic acid was first covalently bound to the soybean ferritin outer surface to fabricate a caffeic acid-ferritin complex (CFRT) by alkali treatment (pH 9.0). A decreased content of free amino acid (0.34 µmol/mg) and increased polyphenol binding equivalent (63.76 nmol/mg) indicated the formation of CFRT (ferritin/caffeic acid, 1:80). Fluorescence and infrared spectra verified the binding of caffeic acids to the ferritin structure. DSC indicated that the covalent modification enhanced the thermal stability of CFRT. Besides, CFRT maintained the typically spherical shape of ferritin (12 nm) and a hydration radius of 7.58 nm. Moreover, the bioactive colorant betanin was encapsulated in CFRT to form betanin-loaded CFRT (CFRTB), with an encapsulation rate of 15.5% (w/w). The betanin stabilities in CFRTB were significantly improved after heat, light, and Fe3+ treatments, and its red color retention was enhanced relative to the free betanin. This study delves into the modifiable ferritin application as nanocarriers of dual molecules and gives guidelines for betanin as a food colorant.

Casein phosphopeptide interferes the interactions between ferritin and ion irons.

Ferritin, a vital protein required to store iron in a cage-like structure, is critical for maintaining iron balance. Ferritin can be attacked by free radicals during iron reduction and release, thereby leading to oxidative damage. Whether other biomacromolecules such as casein phosphopeptides (CPP) could influence the ferritin's function in iron oxidation and release and affect the ferritin stability remains unclear. This study aims to investigate the effect of CPP on the ferritin­iron ion interaction, thereby focusing on role of CPP on ferritin stability. Results showed that CPP weakened the iron oxidation activity of ferritin but promoted iron release. Moreover, CPP could effectively chelate iron, capture hydroxyl radicals, and reduce the degradation of ferritin. This study highlights the role of CPP in the ferritin­iron relationship, and lays a foundation for understanding the interaction between ferritin, peptides, and metal ions.