Calcium-binding capacity of peptides obtained from sheep bone and structural characterization and stability of the peptide-calcium chelate

This study was aimed to obtain calcium-binding peptides with the enzymatic hydrolysis of sheep bone. The peptide of molecular weight from 3 to 10 kDa (SBP3) obtained by alkaline protease had the highest calcium-binding capacities which were mainly due to high levels of residues of Asp, Glu, Arg, Lys, Ser, Leu and Phe. The optimal conditions for the preparation of peptide-calcium chelate (SBP3-Ca) were temperature of 50 °C, pH value of 8, mass ratio of peptide/calcium of 3:1 for 55 min by response surface methodology determined, under which calcium chelating rate of 89.56% was obtained. The spectral results showed that peptides are combined with calcium through the interaction between the amino nitrogen atom and carboxyl oxygen atom. The scanning electron microscope and particle size analyses demonstrated that after peptide was combined with calcium ions, the microstructure was changed and the spatial structure was folded, which reduced the particle size with the formation of irregular particles.SBP3-Ca exhibited excellent stability in the presence of oxalic acid, phytic acid and in vitro simulated gastrointestinal environment. The present study provides a basis for the utilization and development of sheep bone peptide calcium chelate as a functional ingredient.