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Functional and biochemical properties of fish protein hydrolysates (FPH) from blue whiting (BW) were studied. FPH (2.5%, 5%, 10%, and 15% degree of hydrolysis [DH]) were made from isolated proteins from headed and gutted BW with Alcalase 2.4 L. The properties of dried BW mince and protein isolate compared to 4 reference proteins (soy and milk protein) were studied: color, solubility, water-holding capacity (WHC), oil-binding capacity (OBC), emulsion capacity (EC), and emulsion stability (ES). The angiotensin I-converting enzyme (ACE) inhibitory activities of the soluble fraction of BW powders were also investigated. Furthermore, the products were characterized by analyzing their chemical composition. Chemical composition, solubility, OBC, and EC of the BW powders was significantly (P < 0.05) different with different DH, while color, ES, and WHC were not significantly (P > 0.05) different. Salt content of the FPH was high (4% to 19%) and increased with increased DH. Protein solubility varied from 10% to 70% and increased with increased DH. WHC of the FPH was around 97% and was higher than that of all the reference proteins tested. OBC decreased with increased DH (from 3.5 to 2.1 g oil/g protein) and was higher than OBC of the soy and milk proteins (1.6 to 1.9 g oil/g protein). EC of FPH was similar or lower than the reference proteins. ES of FPH (60% to 90%) was similar to or lower than soy and whey proteins (60% to 98%) but higher than casein (20%). ACE inhibition activity increased as DH was increased. Practical Application: The results from this study demonstrate that a functional bioactive hydrolysate can be produced from BW, which is an underutilized fish species, and may aid the industry in better utilizing this raw material. The novelty of this research was the use of BW as a raw material where the protein has been isolated with the pH shift method. Furthermore, it was novel that bioactivity and functionality was measured in the same samples.

The results indicate that the F. vesiculosus extract has a potential as an excellent natural antioxidant against lipid oxidation in fish muscle foods while protein hydrolysates are more promising for fish oil emulsions. The usefulness of in vitro assays to predict the antioxidative properties of new natural ingredients in foods thus depends on the knowledge about the food systems, particularly the main pro-oxidants present.

The raw materials that come from traditional fisheries and aquaculture can be regarded as a great and valuable source of proteins both for animal and human nutrition. Fish meal, fish sauce, surimi and fish silage are traditional protein based products. Over 6 million tonnes of fishmeal is produced worldwide each year from about 25-30 million tonnes of industrial fish (Fish Meal Information Network, 2007). The demand is increasing with the growth in aquaculture and the price has been rising (Klinkhardt, 2006). About 2-3 million tons of wild fish is processed each year worldwide into about 750 000 tonnes of surimi. It has doubled in the last 10 years (GRP, 2007). Fish sauce is produced in a quantity of about 400 000 tonnes each year (Dissaraphong et al., 2006). Fish silage is almost entirely used for feed. Norway is the major fish silage producer-producing about 140 000 tonnes pr year, mainly from aquaculture by-products (Rustad, 2003). 2004; Nishioka and Shimizu, 1983). Chemical processing methods for protein recovery have been extensively reviewed in two recently published books (Hultin et al., 2005 and Shahidi ed.2006). The SuspenTec ® process is an automated method of reducing fish trimmings at low temperatures (-(4-6) °C) to micron-sized particles and incorporating them into traditional brines to create homogeneous suspensions. The controlled temperature ensures efficient protein binding and dispersal of suspension into the whole-muscle product (Christensen, 2006). The pH-shift protein isolate can be added to fresh seafood of the same species by needle injection into fillets, static soaking, or vacuum tumbling. Another interesting aspect is NutraPure® protein processing a technology to reduce fat in deep-fried fish products (Kelleher and Williamson, 2007; www.proteusindustries.com). Acid and alkali extracted fish protein isolates have a GRAS (Generally Regarded as Safe) status in the United States (FDA, 2004). The pH shift methods are an alternative to surimi production. They are more suitable than the surimi process for complex raw materials like whole fish and co-products. The process is shown in figure 1. It involves solubilising muscle proteins by subjecting diluted finely homogenized fish meat to either very low pH (~2.5-3) or a very high pH (~10.8-11.2) at low temperatures. Solids such as bones, scales, neutral fat and disrupted cellular lipid membranes are then removed by centrifugation. The soluble protein is then precipitated by adjusting the pH to the isoelectric point of the myofibrillar proteins to give a protein isolate (Kristinsson et al., 2006). The method gives higher yield of proteins than surimi processing. Sarcoplasmic proteins, that are washed away in surimi processing, are mostly recovered in the pH-shift process (Choi and