Co-production of gelatin, hydroxyapatite and calcium-binding peptides from Tilapia scales: Structural characteristics and physicochemical properties.

A novel co-production strategy was developed to valorize tilapia scale waste into gelatin (TSG), hydroxyapatite (TSHA), and calcium-binding peptides. TSG was obtained by hot-water extraction, and the residues were calcined at 700 °C for 3 h to produce TSHA, which served as a self-prepared affinity medium. Alkaline protease hydrolysis yielded the highest calcium-binding capacity (CBC, 4.86 μg/mg). After TSHA-based affinity purification, the recovered fraction (THAC) showed improved CBC (5.71 μg/mg). Isothermal titration calorimetry suggested spontaneous and exothermic calcium-binding (Ka = 2.4 × 104 M-1; n = 2.26). Spectroscopic analyses demonstrated Ca2+ coordination through carboxyl groups. The b and y fragments of the representative peptide (GDDGE, DVSGGYDE, GEPGDDGAK, and GDRGDEGPK) were analyzed. Molecular docking revealed distinct Ca²⁺-binding modes involving carboxylate and backbone carbonyl oxygens. This strategy provides a feasible route for converting aquaculture by-products into value-added calcium-binding peptide ingredients.