Abstract
Catfish bone powder (CBP), prepared from catfish head, was a good source of natural minerals, particularly calcium (Ca) and phosphorous (P). The Ca content were higher than P when analyzed by either chemical or SEM in EDS mode. These elements were found in the crystal form of hydroxyapatite (HA) complex with protein, as assessed by spectroscopic techniques, including XRD and FT-IR. Thus, low Ca solubility was thus observed at 0.03 ± 0.0038 % and digestion of complex HA is required for more liberation of Ca. Citric acid was therefore applied for Ca extraction using a microwave-assisted method. The conditions were optimized using response surface methodology with central composite design to evaluate the effect of extraction time, microwave power, citric acid concentration, and CBP weight. Based on a linear prediction model, the optimum condition to extract Ca from 0.4 g of CBP was at 0.1 M citric acid using microwave power of 275 W for 60 s. This condition provided a Ca content of 1.11 mg/mL in solution, which extract calcium about 27.75 % from original CBP weight. This Ca concentration was enough to induce alginate drops (1.0 %) to form hydro-beads, indicating its functional property in food system. These results provided the promising method to extract natural calcium from fishery by-products for further creating innovative food products.