The marine crustacean krill (order Euphausiacea) has not been a traditional food in the human diet. Public acceptance of krill for human consumption will depend partly on its nutritive value. The aim of this article is to assess the nutritive value and potential health benefits of krill, an abundant food source with high nutritional value and a variety of compounds relevant to human health. Krill is a rich source of high-quality protein, with the advantage over other animal proteins of being low in fat and a rich source of omega-3 fatty acids. Antioxidant levels in krill are higher than in fish, suggesting benefits against oxidative damage. Finally, the waste generated by the processing of krill into edible products can be developed into value-added products.

Solubility of rainbow trout proteins was determined between pH 1.5 and 13.0 and various ionic strengths (IS). Minimum solubility occurred at pH 5.5; however, when IS = 0.2, the minimum solubility shifted toward more acidic pH. Isoelectric solubilization/precipitation was applied to trout processing byproducts (fish meat left over on bones, head, skin, etc.), resulting in protein recovery yields (Kjeldahl, dry basis) between 77.7% and 89.0%, depending of the pH used for solubilization and precipitation. The recovered protein contained 1.4-2.1% ash (dry basis), while the trout processing byproducts (i.e., starting material) 13.9%. Typical boneless and skinless trout fillets contain 5.5% ash, and therefore, the isoelectric solubilization/precipitation effectively removed impurities such as bones, scales, skin, etc., from the trout processing byproducts. The recovered proteins retained gel-forming ability as assessed with dynamic rheology, torsion test, and texture profile analysis (TPA). However, the recovered proteins failed to gel unless beef plasma protein (BPP) was added. Even with BPP, the recovered protein showed some proteolysis between 40 and 55 degrees C. Addition of potato starch, transglutaminase, and phosphate to the recovered proteins resulted in good texture of trout gels as confirmed by torsion test and TPA. Higher ( P < 0.05) shear stress and strain were measured for gels developed from basic pH treatments than the acidic counterparts. However, proteins recovered from acidic treatments had higher ( P < 0.05) lipid content than the basic treatments. This is probably why the gels from acidic treatments were whiter ( L* - 3 b*) ( P < 0.05) than those from the basic ones. Our study demonstrates that functional proteins can be efficiently recovered from low-value fish processing byproducts using isoelectric solubilization/precipitation and subsequently be used in value-added human foods.

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This study demonstrated that the novel isoelectric solubilization/precipitation can be applied to recover functional muscle protein in a continuous mode from whole Antarctic krill. Protein recovered from whole krill had a much lower ash content than whole krill, suggesting good removal of inedible impurities (shell, appendages, etc.). Lipids were retained to a higher degree with krill protein solubilized at acidic rather than basic pH. The viscoelastic modulus (G') showed that recovered krill protein failed to form heat-induced gel unless beef plasma protein (BPP) was added. Therefore, protease inhibitors are suggested for development of krill-derived products. Even with BPP, the G' decreased between 45 and 55 degrees C. However, krill protein solubilized at acidic pH had a higher decrease of the G' than the protein solubilized at basic pH, likely due to krill endogenous cathepsin L. Krill protein-based gels developed from protein solubilized at basic pH, especially pH 12.0, had better texture (torsion and Kramer tests and texture profile analysis) than acidic counterparts, possibly due to higher proteolysis and denaturation at acidic pH. Gels made from protein solubilized at acidic pH were brighter and whiter likely due to a higher lipid content.