Abstract: The preparation and digestion stability of calcium-chelated cod bone gelatin peptides were investigated in this study. The optimal parameters for chelating cod bone gelatin polypeptides with CaCl2 were obtained by using a 3-factor 3-level Box-Behnken experimental design with response surface methodology as follows: after the gelatin was hydrolyzed at 50 ℃ for 1.5 h, the hydrolysate and CaCl2 were mixed at 50 ℃ at a mass ratio of 8:1 for 1 h and adjusted to pH 5.5. Then, after reaction, the samples were collected by precipitating the calcium-chelated cod bone gelatin polypeptides with pure ethanol, and dehydrated by vacuum freeze drying. The chelating rate was 93.47%. Scanning electron microscope showed that the microstructure of cod bone gelatin polypeptides changed dramatically after chelated with Ca2+, turning from coarse fibers into smooth spherical granules. Fourier transform infrared spectroscopy analysis suggested that after chelated with Ca2+, the spectra of gelatin peptides and its calcium-chelated form changed dramatically, indicating the occurrence of chelating reaction between gelatin peptides and Ca2+. The calcium chelating rate of cod bone gelatin polypeptides decreased from 60.74% to 3.64% after simulated gastric digestion (pH 2.0) for 120 min because H+ competed for the binding sites with Ca2+, causing damage to the calcium-chelated form. The chelating rate increased from 10.74% to 53.38% after 120 min simulated intestinal digestion. However, there was almost 50% of free Ca2+ in the system, suggesting that the chelated structure is sensitive to the gastric environment but remains relatively stable in the intestinal system. The results of this study can provide theoretical support and technical reference for the development of new calcium supplements and for the high-value utilization of aquatic product processing byproducts.

Key words: gelatin peptide, calcium, chelating, response surface optimization, simulated gastrointestinal digestion