Industrially implemented in northern Europe (mainly Iceland and Scandinavia) a century ago to manage herring fishery wastes, the production of fish meal and fish oils were – and still are – traditional ways of valorizing by-products generated by the fishing industry. Extensible also to the co-products produced in the de-heading, gutting and filleting of the heads, viscera and frames of farmed fish (salmon, trout or sea bass), fish meal plays a fundamental role in the productive system of the aquaculture industry as final receptors (managers) of their wastes, and producers of the aforementioned compounds. The market value of fish meal is a function of its level of protein, and fish oils are more valued the higher the concentration of omega-3 fatty acids, especially docosahexaenoic acid (DHA). Both products are essential ingredients in aquaculture feed formulations.
However, other alternatives and processes of valorization can be applied to these substrates: the production of fish protein hydrolysates (FPHs) and marine peptones generated from all wastes, the recovery of collagen and gelatin from the skins or hydroxyapatites of the fish bones. Within the framework of the GAIN project, the Marine Research Institute (IIM-CSIC, Vigo, Spain) is developing and optimizing these alternatives, initially on a lab scale, and scaling some of them in the pilot plant available in the IIM-CSIC. The raw materials studied are heads, trimmings, frames and viscera from rainbow trout, salmon, turbot and carp.
In the first case, the production of FPHs consists in the application of proteases, mainly exogenous, to the mixing of the crushed wastes with water working under optimal experimental conditions (pH, T, enzyme concentration, etc.) for the adequate enzymatic hydrolysis of the substrates. The solid hydrolysates generated after the separation of the bones and oils present in the initial substrates and the drying process are a highly digestible protein-rich material, with a varied set of peptides of different sizes, in some cases with certain bioactive properties and better nutritional characteristics than the fish meal used as ingredient in aquaculture feed. It is in this direction where the application of the FPHs produced in the IIM-CSIC will be focused: the preparation by SPAROS of new formulations for aquaculture feed based, among other ingredients, on FPH’s. Additionally, hydrolysates from individuals of blue whiting discarded by European fishing fleets and which must be landed to the ports following the new EU fishing policy (Landing Obligation) will also be evaluated in salmonids feed.
The second of the examples consists in the production of marine peptones from the FPHs after stages of autoclaving and centrifugation. These fluids rich in protein material should be a source of organic nitrogen of great potential in the formulation of nutritive media for the cultivation of bacteria with important technological applications (probiotics, dairy starters, producers of bacteriocins and lactic acid, etc.). On the other hand, collagen and gelatins that can be recovered from fish skins, combining different chemical, enzymatic and thermal purification/extraction steps, could be biomaterials of interest in pharmacological, nutraceutical and food sectors. Finally, thermally processed clean bones of muscular debris, should have a composition rich in calcium phosphates with possibilities of application as a food supplement, incorporated into fertilizers or as bioapatites for bone regeneration.
We hope that the processes that will be developed within GAIN will lead to other alternatives, economically more profitable, for the management of aquaculture by-products beyond the well-established production of fish meal.