Synthesis and characterization of collagen and hydroxyapatite derived from tuna by-products as biomaterials

Utilizing marine by-products offers a sustainable approach in reducing fish-processing waste while generating value-added materials. Tuna bone by-products, rich in macro- and micronutrients, were investigated as a source of collagen and hydroxyapatite (HAp). In this study, acid solubilization was used to extract collagen from tuna skeletal by-products, while HAp was synthesized through calcination and ultrasonication processes. The extracted acid-soluble collagen (ASC) exhibited a characteristic absorption peak at 225 nm and retained its triple-helical structure, layered-sheet microstructure, and porous, slightly wrinkled morphology. HAp obtained via calcination showed sharper diffraction peaks, higher crystallinity, and larger crystallite size, whereas the ultrasonicated sample exhibited reduced crystallinity and smaller crystallite size. The crystallite sizes of calcined samples 1, 2, and 3 and the ultrasonicated sample were 16.64, 15.62, 16.63, and 4.39 nm, respectively, with crystallinity indices of 0.643, 0.572, 0.613, and 0.027. Their Ca/P ratios were 1.753 ± 0.052, 1.806 ± 0.074, 1.792 ± 0.021, and 1.935 ± 0.091, respectively. Among the tested conditions, calcined sample 1 (2 h isothermal treatment) showed the Ca/P ratio closest to stoichiometric hydroxyapatite. These findings demonstrate that tuna bone by-products can serve as a promising raw material for recovering collagen and HAp with tunable physicochemical characteristics, supporting future value-added biomaterial development and sustainable marine waste utilization. • Tuna bone by-products were valorized as sources of collagen and hydroxyapatite (HAp). • Acid solubilization effectively recovered collagen from tuna bone by-products. • Calcination and ultrasonication controlled the crystallinity and crystallite size of HAp. • Calcined HAp showed a Ca/P ratio close to that of stoichiometric hydroxyapatite. • The study supports the sustainable conversion of fish-processing waste into materials.