Leftovers (e.g., fish bone, skin, and fish viscera) from fish processing are causing increasing environmental problems with the rapid growth of the global fishing industry (Marliana et al., 2015). These leftovers, however, are rich in nutrients, such as proteins, lipids, and minerals. Fish bones are a major by-product of fish processing and are a potential biological source of natural inorganic calcium (Xu et al., 2020). Some research has been undertaken on the utilization of calcium from fish bones, for example, using it to make calciumfortified food. However, conversion of fish bones into a bioavailable form of calcium that is easily absorbed from the digestive system is difficult, and there is a clear need for effective processing methods to achieve this industrially (Li et al., 2020;Yin et al., 2015).Mackerel (Trachurus trachurus), a low-value bulk fish, has been used as a source of fish bones for processing to extract calcium (Ferraro et al., 2013). Calcium in Mackerel bones is in the form of hydroxyapatite (HA) and β-tricalcium phosphate (Terzioglu et al., 2018).The main components of fish bones are the inorganic phase (calcium phosphate, CaP) ceramics (mainly hydroxyapatite (HA) crystals) and the organic/protein phase (mineralized collagen fibrils, MCFs), which form a complex matrix (Xu et al., 2020). The MCFs (mainly collagen-Ⅰ, 90%) have a triple helical collagen structure and act as an adhesive, strongly binding to hydroxyapatite, and giving the bone stiffness and