Fish and fish side streams are valuable sources of high-value components

The current practice of fish processing generates increasing quantities of side streams and waste,such as skin,heads,frames,viscera,and fillet cut offs.These may account for up to 70%of the fish used in industrial processing.Low-value fish catches,and under-utilized fish species comprise another source of side streams.These side streams have been discarded in the environment leading to environmental problems or they have ended up as low commercial value products,such as feed for fur animals and aquaculture.However,several studies have shown that fish side streams contain valuable bioactive ingredients and fractions,such as fish oils,proteins and peptides,collagen,gelatin,enzymes,chitin,and minerals.These compounds and fractions may provide the opportunity to develop novel applications in health promoting foods,special feeds,nutraceuticals,pharmaceuticals,and cosmetic products.Better utilization of side streams and low-value fish would simultaneously improve both the environmental and ecological sustainability of production.This review summarizes the current knowledge on fish and fish side streams as sources of high-value components such as peptides with antimicrobial,antioxidative,antihypertensive,and antihyperglycemic properties,proteins such as fish collagen and gelatin,fish enzymes,fish oils and fatty acids,polysaccharides like glucosaminoglycans,chitin and chitosan,vitamin D,and minerals.Production technologies for recovering the high-value fractions and potential product applications are discussed.Furthermore,safety aspects related to the raw material,technologies,and fractions are considered.

Conversion of fish processing wastewater into fish feed ingredients through submerged cultivation of Aspergillus oryzae

Fish processing towards production of fillet gives rise to wastewater streams that are ultimately directed to biogas production and/or wastewater treatment.However,these wastewater streams are rich in minerals,fat,and proteins that can be converted to protein-rich feed ingredients through submerged cultivation of edible filamentous fungi.In this study,the origin of wastewater stream,initial pH,cultivation time,and extent of washing during sieving,were found to influence the amount of recovered material from the wastewater streams and its protein content,following cultivation with Aspergillus oryzae.Through culti-vation of the filamentous fungus in sludge,330 kg of material per ton of COD were recovered by sieving,corresponding to 121 kg protein per ton of COD,while through its cultivation in salt brine,210 kg of material were recovered per ton of COD,corresponding to 128 kg protein per ton of COD.Removal ranges of 12-43%,39-92%,and 32-66%for COD,total solids,and nitrogen,respectively,were obtained after A.oryzae growth and harvesting in the wastewater streams.Therefore,the present study shows the versatility that the integration of fungal cultivation provides to fish processing industries,and should be complemented by economic,environmental,and feeding studies,in order to reveal the most promising valorization strategy.