Improving calcium bioavailability from fish bone waste: the role of sodium hydroxide in bio‑calcium extraction from tilapia (Oreochromis niloticus) bones

Calcium deficiency is a global health issue motivating the search for sustainable calcium sources from aquaculture waste. This study investigated sodium hydroxide (NaOH) concentration effects on bio‑calcium quality and bioavailability extracted from tilapia ( Oreochromis niloticus ) bones. Tilapia bones were treated with 0.5 M, 1 M, and 2 M NaOH solutions for 30 min compared to untreated controls. Increasing NaOH concentrations decreased yield while improving brightness, ash content, and calcium bioavailability. The 2 M NaOH treatment produced bio‑calcium with highest calcium bioavailability (8.57 %), surpassing both control (7.26 %) and commercial calcium carbonate (0.72 %) by 12-fold. Higher NaOH concentrations reduced moisture, protein, and fat contents while increasing hydroxyproline and decreasing lipid oxidation. SEM showed smoother surfaces with homogeneous pores in 2 M NaOH-treated samples. FT-IR and EDS confirmed consistent hydroxyapatite structure. This optimization provides a sustainable approach for converting fish waste into high-bioavailability calcium supplements, supporting circular economy in aquaculture while addressing global calcium deficiency. • NaOH concentration affects quality and bioavailability of tilapia bone bio-calcium. • 2 M NaOH treatment yields bio-calcium with 8.57 % calcium bioavailability. • Higher NaOH concentrations improve brightness, ash content, and Ca bioavailability. • 2 M NaOH treatment increases surface porosity and erosion (SEM analysis). • Tilapia bio-calcium has consistent hydroxyapatite calcium phosphate (FT-IR, EDS).