Preparation and characterization of collagen polypeptide chelated calcium from fishbone powder of channel catfish, Ictalurus punctatus

Calcium is essential for living organisms. Even with an apparently sufficient intake of dietary calcium, there is some concern that inadequate calcium is absorbed by the small intestine, due to precipitation of insoluble calcium salts in the neutral to slightly basic intestinal lumen. Some studies revealed that peptides have the capacity to chelate Ca and to prevent the precipitation of insoluble calcium salts, thereby increasing the amount of soluble Ca availability for absorption across the mucosa. However, the mechanism and degree of calcium ion binding are still unclear. In this paper, the combinations between collagen polypeptide (from the enzymatic hydrolysate of channel catfish bone powder) and calcium ion were studied by measuring chelate rate. On the basis of results of single-factor experiments, the Box-Behnken central composite design and response surface method were adopted to obtain the optimum conditions for chelate. The optimal chelate conditions were determined as: chelate temperature 60℃, chelate pH 5.4, chelate time 1.5 h and ratio of collagen polypeptide to calcium 2:1 (w/w). Under the optimized conditions, the chelate rate of Ca-collagen polypeptide could achieve to 82.53％. The formation of Ca-collagen polypeptide chelate was confirmed by the UV-VIS and FT-IR spectra. The characterization of amino acid composition of the chelate was similar to typical collagen-like protein. This research provides a practical guideline and theoretical basis for fully excavating fish bone protein resources and developing the deep processed products.