Simultaneous extraction of calcium phosphates and proteins from fish bones. Innovative valorisation of food by-products

By-products of the fish industry can be a source of valuable molecules, with different technological applications. Fish bones contain both organic and inorganic phases (collagen/other proteins and calcium phosphate minerals respectively), with several uses and among them in cosmetics and medicine. Using the common extraction protocols, only one of the two phases can be extracted, while the other one is degraded. In the present work a method of extraction which allows the obtainment of both proteins and calcium phosphates was developed. Bones from two different species (salmon and sea bream) were tested. Saline solutions based on (NH4)HCO3/(NH4)2HPO4 or (NH4)HCO3 were employed for the protein extraction. Analysis of the organic phase showed that the main extracted proteins were collagen in its different forms (especially α-1); some differences were observed between salmon and sea bream and between the methods of extraction. As for the mineral phase, after calcination at 700 °C, single phase hydroxyapatite was obtained with (NH4)HCO3 solution, while the use of (NH4)HCO3/(NH4)2HPO4 led to a biphasic material of β-tricalcium phosphate and β-calcium pyrophosphate. Biocompatibility tests performed on both organic and inorganic extracts (with fibroblast and osteoblast-like cellular lines) showed their non-toxicity and, hence, their potential suitability for cosmetic or biomedical applications. This work shows that it is possible to obtain a more complete valorisation of the fish bones, with the simultaneous extraction of organic and inorganic valuable compounds. The principles of this process could be applied also to bones of other species, with a positive impact on the environment for the reduction of the wastes and a better use of all available resources.