Improving the utilisation and quality of low value fish (Brachydeuterus auritus and Dactylopterus volitans) by processing

Abstract

Two pelagic underutilised fish species in Ghana, the Burrito (Brachydeuterus auritus) and the flying gurnard (Dactylopterus volitans) were selected for study. Proximate composition analysis indicated high protein content (18-22%), an excellent amino acid profile with high levels of lysine (7-8%) as well as poly unsaturated fatty acids predominantly 20:5ro3 and 22:6ro3 (omega 3 fatty acids), which constituted between 44 and 51% of the total fatty acids. Sodium dodecyl sulfate (SDS) polyacrylamide gel ). electrophoresis of the myofibrillar extracts showed that both fish species may be distinguished from each other by protein bands with molecular weights estimated to be 18,400 and 14,300 daltons. Rheological methods, differential scanning calorimetry (DSC), phase contrast microscopy and FT-Raman spectroscopy indicated a positive synergistic interaction between flying gumard proteins and cowpea flour resulting in greater than expected elastic modulus values. The networks were compatible and stabilized by hydrophobic and hydrogen bonds as well as disulfide bonds. Optimum gels were formed with flying gumard fish and cowpea flour mixed in the ratio of 5:5(w/w) and Burrito fish mince to cowpea flour ratio (2:8 w/w). Interactions of the fish minces with cassava starch resulted in phase separation and weak non-covalent interactions. Infant weaning food formulations including flying gumard mince and other food ingredients showed good nutritional and low viscous properties which compared favourably with commercial infant foods. The shelf life of the products was enhanced with the exclusion of oxygen in vacuum-packed foil packaging. High bloom (275 g) gelatin was produced from flying gurnard fish skin and compared favourably with gelatins from other sources. Using a low cost single screw food extruder built for developing countries, fish based extruded snack pellets incorporating minced burrito: cassava starch, were successfully developed at a barrel temperature of 120°C. Extruded snack products stored in aluminium foil pouches were better protected in terms of chemical changes in free fatty acids and TBARS formation, than those packaged in polyethylene pouches. This development of fish-based extruded products will lead to new products of high nutritional quality and acceptability as shown by chemical and sensory evaluation results