Isolation of hydroxyapatite from Atlantic salmon processing waste using a protease and lipase mixture

There is a need to solve ongoing waste management issues in food processing industries. The demand for fish, including salmon, is higher than ever because of the growing global population and protein needs, however this results in large quantities of wasted by-products. This waste is problematic because it is potentially harmful to the environment and results in significant disposal costs for industries. The salmon frame (bones) is disposed of during processing but is a potential feedstock for hydroxyapatite, a mineral for value-added applications. While previous research has accessed hydroxyapatite from animal wastes, these processes either use very high temperatures or chemicals that are more costly and hazardous than the method described herein. In this study, we developed an enzymatic treatment using a protease and lipase simultaneously to clean the residual meat from salmon frames to isolate collagen-containing hydroxyapatite (sHAP) using Design of Experiment (DoE) under benign conditions. The parameters were optimized using 23 and 24 factorial designs by varying the temperature from 25–55 °C, the enzyme loadings from 0.5–25 μL g−1, and the reaction time from 1–24 h. It was determined by characterization techniques, weight loss calculations, and thermogravimetric analysis that the meat from the salmon frame was successfully hydrolyzed with 15 μL g−1 Neutrase and 7.5 μL g−1 Lipozyme CALB L in 40 °C tap water for 6 h. We have performed a life cycle analysis to compare the current method with previously reported processes used to treat fishery waste. The method reported herein is less impactful (environment, hazard, cost, carbon footprint) than others in the literature, as there are no organic solvents required, enzymes are easily disposed, and temperatures do not exceed 100 °C during the entire process. Furthermore, the optimized conditions were then used on a larger scale and up to 15 salmon frames were easily processed at one time.