Evaluation and Utilisation of Fish Protein Isolate Products

Literature Review1. INTRODUCTIONMany efforts have done both in academy and in industry during recent decades to recoveror isolate protein from fish by-products and underutilised fish species (Kristinsson et al.,2006). A new technology has been developed to increase fish-based protein food forhuman consumption. According to Thorkelsson et al., (2008) this innovation which iscalled the acid and alkali processes or pH-shift method has been documented anddeveloped by Batista (1999); Hultin and Kelleher (1999); and Hultin et al., (2005). Thistechnology also has been introduced and described in three recently published books (ParkJW, 2005; Shahidi F, 2006; and Borresen T, 2008).Much research has been done using this method to isolate protein from fish by-productsand under-utilised fish species. Since introducing pH-shift processes to the seafoodindustry more than 90 scientific papers, patents and MSc. /PhD thesis have been published.Most of these documents describe the acid-aided or alkali-aided processes to recoverprotein from fish by-products and underutilised fish or describing the specifications ofisolated proteins. Only little information has been published on utilization of fish proteinisolate products (Thorkelsson et al., 2008, and Nolsoe and Undeland 2008). This chapterdescribes the pH-shift process at a glance, its advantages vs. surimi and the literature on theutilisation of isolated fish protein products2. pH-SHIFT PROCESS FOR ISOLATING FISH PROTEINSThe basic outline of pH-shift method is simple. According to Hultin et al., (2005) the mostimportant steps of this method are as follows:A-Solubilisation of proteins at low or high pH;B-Removing fat and impurities by using high-speed centrifuge; and finallyC- Precipitation of the proteins at their isoelectric point.In this process as shown in figure 1, fish flesh is first solubilised in alkali or acid after theraw material has been mechanically deboned and minced or chopped to a small particlesize. Solubilisation is done by using 5 to 10 volumes of water with alkali or acid added toobtain approximately pH 2.5 or 11 for example. The mixture is then centrifuged to removeoil and other insoluble material. Precipitation of proteins is accomplished by adjusting pHto 5.2 to 5.5. Protein isolate is sedimented by using a high speed centrifuge (Hultin et al.,2005). FPI can be frozen like surimi or mince for further use. Figure 2 presents a frozenblock of fish protein isolate.2