Abstract
Cape horse mackerel (Trachurus capensis) is an underutilized pelagic fish from Namibia. In this study, the physico-chemical characteristics, nutritional composition and functionality (thermal and rheological) properties of horse mackerel and local cereals found in Namibia were investigated. This knowledge of the physico-chemical composition and functionality of these ingredients and their behaviour in mixed food model systems was applied to optimize the extrusion process, used to make snack foods. Proximate, biochemical, amino acid and fatty acid analyses, and differential scanning calorimetry (DSC), rheology and Raman spectroscopy studies were conducted on horse mackerel mince, cassava, maize, pearl millet flour, mixtures of these ingredients, an extruded horse mackerel snack and a commercial shrimp cracker. Differences in the protein bands identified by Raman spectroscopy provided detailed information on the protein structure of the raw materials, protein denaturation and gel formation of the extruded snacks. Products of similar textural properties were developed despite the varying composition of mixtures. A mixture comprising 20% horse mackerel, 20% maize flour, 30% pearl millet flour and 30% cassava flour showed the optimum starch and protein interactions as evidenced by thermal and rheological properties; this formulation was used to develop the horse mackerel extruded snack. Extrusion provided an efficient method for combining essential protein and lipids from fish and starchy cereal mixtures into a balanced and nutritious snack food. The horse mackerel extruded snack product had a higher protein quality compared to the commercial shrimp cracker. The raw material quality used in the development of an extruded horse mackerel snack significantly influenced its final quality and total cost. Poor quality fish used in the processing of the extruded horse mackerel snack resulted in an increase in failure costs and consequently the total quality cost. Failure costs decreased from 80% to 40% of Total Quality Costs when good raw material was used.