Abstract
The aim of this thesis was to develop a food recipe for the developing countries using underutilised fish species. The food was freeze-dried and stored at 22°C with and without antioxidants. Lipid oxidation and safety of the fish used in the recipe were assessed. The lipid and protein content were at 5% and 19.9% respectively for mackerel and at 2% and 21.6% respectively for horse mackerel. The moisture content was approximately 71% for both fish. Raman spectra of oil extracted from freeze-dried mackerel and horse mackerel revealed significant reductions in the intensity of bands associated with CH2 stretches and C=O ester stretches and increase in the intensity of the bands at 3011 cm-1 and 2960-2850 cm-1 suggesting alterations in lipid structure involving CH groups, as a result of lipid oxidation confirmed by peroxide value determinations. Combination of vitamins E + C + citric acid (250; 250; 100 ppm) was shown to be the most effective in slowing lipid oxidation in fish (P < 0.05) and in food products (P < 0.01). A rapid decrease (P <0.01) in solubility of myofibrillar proteins was detected in the control samples. Gel electrophoresis of myofibrillar proteins of freeze-dried mackerel showed a gradual loss of the myosin band in control samples. Addition of methyl linoleate (ML) or mackerel oil oxidized under UV light for 72 hours caused a substantial drop in the percentage of LDH release. Combination of vitamins E + C + citric acid (250; 250; 100 ppm) as well as rosemary (250 ppm) showed a significant decrease in the percentage of LDH release compared with the control (without antioxidants) group (P < 0.01 and P < 0.05 respectively). The data showed that fish from African and Asian marine waters contain PCDD/Fs at levels significantly below the limit set by the European Commission. An assessment of dietary exposure to PCBs and Dioxins showed a daily intake per capita of these contaminants below the tolerable daily intake (TDI) and tolerable monthly intake for dioxins established by World Health Organisation.