Mechanism on releasing and solubilizing of fish bone calcium during nano‐milling

Abstract Fish bone, predominately composited by collagen and hydroxyapatite (HAP), is a natural calcium resource that possesses the potential to be used as functional ingredient in food application. In this study, five HAP suspensions with either collagen or amino acids were applied to simulate the releasing and solubilizing of fish bone calcium during nano‐milling. As milling time was increased, particle sizes from five suspensions gradually decreased and pH increased. The sizes and pH kept constant as the time was extended beyond 60 min ( p < .05). Initial soluble calcium content of HAP suspension fluctuated with milling time and was not increased after milling for 240 min. However, soluble calcium contents of HAP suspensions with collagen and amino acids continuously increased and reached the highest values of 106.70 and 147.34–645.68 μg/g, respectively. After nano‐milling, crystallinity of HAP particles declined and calcium element on the surface decreased and contents of free amino acid and peptides from fish bone suspension significantly increased ( p < .05). Our results suggested that the releasing and solubilizing of fish bone calcium during nano‐milling was mainly attributed to alterations on size and crystalline structure of HAP, and the chelating effects by amino acids and peptides. Practical Applications Fish bone is the main solid waste from fish processing industry. When properly processed, it possesses the potential to be used as food grade calcium additive. It has been reported that grittiness of fish bone could be neglected after reducing its particle to nanoscale. Furthermore, soluble calcium content was significantly increased, which might be benefit for improving calcium bioavailability of fish bone. However, there is no report regarding the release of calcium from fish bone during nano‐milling process so far. This research will provide scientific foundation for improving solubility of calcium from various natural resources in a physical method.