Evaluation and Utilisation of Fish Protein Isolate Products

1. INTRODUCTIONA fish protein solution (FPS) is a kind of semi-solid protein-in-water colloid which isprepared by using acid/alkaline aided process or diluting FPI with brine. The solution mayinclude salt, and other optional ingredients (cryoprotectants, etc.) based on the final use.From an economical point of view fish by-products are the best raw material for producingFPS and this can improve the utilisation of fish resources.According to Batista et al., (2007) the yields of conventional technologies to manufacturevalue-added fishery products are relatively low and large amounts of by-products are lost.This is a big issue in fish filleting processes where less than 40% of fish tissue is recoveredfor human consumption. Thus, a new process was developed to increase the recovery ofproteins from different sources of raw material (Batista 1999, Hultin and Kelleher, 2000,2001, Hultin et al., 2005).This process can be potentially used for any kind of fish and fishby-products as it presumably removes essentially all the membrane lipids and provides anincreased yield of protein. The improved yield results in less protein in the wastewaterduring industrial processing and less environmental pollution (Batista et al., 2007).This process for isolating fish proteins involves the solubilisation of minced andhomogenized fish tissue either in an acidic (pH ≤ 3.5) or in an alkaline (pH ≥ 10.5)aqueous solution. The protein rich aqueous solution is separated from solids (insolubleproteins, skin, bones, and scales) and neutral lipids by centrifugation. The soluble proteinsare then recovered by isoelectric precipitation by adjusting the pH at 5.5 and theprecipitated proteins are removed by centrifugation (Batista, et al., 2007). Fish proteinisolate and fish protein solutions made by this method can kept chilled or be frozen forfuture utilization.Fish protein solutions can be used for fortification of fish fillets (Thorkelsson et al., (2008).FPS also was applied as a fat blocker in fish fingers and patties (Kim and Park 2006).1.1 Effects of phosphate and pH on functional properties of FPSPhosphate has been added to meat and seafood products to induce water holding capacityduring processing, which has maintained or even increased weight of these products. Theeffectiveness of phosphates on water holding capacity of fish meat products depends on thetype and quality of phosphate. Hunt et al., (2004) reported that phosphates can increaseWHC in fish protein if they are properly added. The activity may be because of effects onpH and ionic strength and specific interactions of phosphate anions with divalent cationsand myofibrillar proteins. Factors such as the concentration of ions (Mg 2+ , Ca 2+ , Cl − ),temperature, and pH are believed to affect how phosphates interact with muscle proteins(Trout and Schmit 1984, Offer and Knight 1988, Lindsay 1996, Chang and Regenstein1997).Knipe (1992) reported that alkaline phosphates increase meat pH in the range of 0.1 to 0.6units, depending on the phosphate (0.1-0.3%) used. The effect of phosphate to change thepH is in descending order of: pyrophosphates, tripolyphosphates, and hexametaphosphates.14