Recovery of proteins from fish waste products by alkaline extraction

Waste from fish-filleting units is used in the production of fish meal or d irectly used in animal feeds but more frequently is simply discarded. In or der to upgrade the by-products of the filleting of hake and monkfish, a sys tematic study was made of the recovery of proteins by chemical extraction a nd precipitation with HCl and sodium hexametaphosphate [Na-6(PO3)(6)]. The extraction process was studied to determine the effect of pH, type of alkal ine solution used [NaOH or Ca(OH)(2)], concentration of NaCl, ratio of extr acting media to raw material, and temperature on the percentage of protein solubilised. Proteins present in the extract were recovered by precipitatio n with HCl and the effect of pH on the percentage recovered was examined. T he effect of Na-6(PO3)(6) concentration on the recovery of soluble proteins present in the supernatant after isoelectric precipitation was also studie d. The raw material and products were characterised by their approximate ch emical composition and amino acid profile.