The effects of freeze-drying and flake freezing of surimi on biochemical and physical properties as affected by various storage conditions were examined. Using three cooking parameters shear stress and strain values were evaluated to measure gelation properties of surimi gels. Stress values increased up to 3 months and then decreased substantially as storage time was extended. In general, strain values decreased substantially over time, however, freeze-dried surimi kept in the freezer at - 18°C did not change during 9 months of storage. Overall, color decreased during storage and b* values of the freeze-dried surimi kept at room temperature increased significantly. Salt extractable proteins decreased while dimethylamine increased. Electrophoretic patterns, however, did not show any apparent damage to the MHC due to frozen storage and/or proteolysis (with 60°C incubation) until the 9th month of storage. At 9 months, a reduction of the MHC was observed and the lower molecular weight bands were more intense. Freeze-dried samples stored in the freezer maintained the highest quality for the duration of the 9 month study. Low temperature storage is important for retaining good functionality in freeze-dried surimi. The effects of cross-section diameter on shear stress and strain and effects of individual variation in measuring diameter were studied. Gelation properties of surimi using milled and molded gels were compared. The possibility of skin formation using various cook times was also evaluated. Shear stress values were significantly affected by diameter accuracy, whereas the effect was not as significant for shear strain values. Individual variation in measurement was also greatly noted. Molded gels resulted in significantly lower strain values than milled samples, whereas stress values were significantly higher in molded gels than in milled gels. Using a lechitin-based spray appeared to eliminate skin formation on all samples. / Graduation date: 2001

Graduation date: 1993

Thesis (D. Tech. Environmental health) -- Central University of technology, Free State, 2011 / Apart from being the primary food source of many cultures around the world, fish contains notable amounts of essential fatty acids that are required by the human body, thus making fish a vital part of the human diet. In South Africa Cape hake is a well-known and highly consumed local fish species, which is transported from coastal areas countrywide where the fresh fish are displayed on ice in various retail stores. Fish is known to be highly susceptible to spoilage and, as a result, the maintenance of the cold-chain in related products is of particular importance. Additionally, recent trends showing a decline in natural fish resources have instigated growing concerns about the sustainability and optimal utilisation of fish as a food source. Against this backdrop, this study aimed at determining the influence of storage parameters on selected triglycerides and their possible metabolic pathways. Also applying prediction modelling of fatty acids and volatiles as instruments to assess exposure of Cape hake fillets to excessive microbial contamination and, in effect, be indicative of the environmental parameters (for example temperature) that may influence such contamination. Randomly selected juvenile hakes were filleted and stored under various simulated retail storage conditions, under either controlled or uncontrolled environmental conditions. For each hake filleted, one fillet was inoculated with an increased load of autochthonous microbiota, and the corresponding fillet was kept at similar temperature conditions. All fillets were monitored over a ten day period, during which fatty acid and volatile samples were collected and analysed. From the resulting triglycerides a selection of fatty acids were profiled and their possible metabolic pathways investigated. Fish maturity, the distribution of the fatty acids and the implication thereof in the nutritional value were also assessed. Conventional chemometric methods utilising mathematical expressions were subsequently utilised in order to predict contamination and whether the cold chain was sustained, while an artificial neural network (ANNs) were designed to predict excessive microbial contamination in the fillets. The results showed that the nutritional value of fish differs notably with its maturity and size. Mathematical equations were furthermore found to be effective assessment instruments to indicate the percentage differences in storage temperature, as well as consequent microbial influences. Thus, this approach may introduce mathematical prediction modelling as a promising mechanism to assess Cape hake spoilage. An artificial neural network (ANN) was successfully designed, that succeeded in distinguishing between Cape hake fillets displayed and stored on ice that have been exposed to excessive contamination and those that have not been exposed. In the latter case, the selected variable was a fatty acid, hexadecanoic acid, used as biochemical indicator. This modulating approach may provide a platform for future shelf-life studies on related muscle tissue. Ultimately, the study endeavoured to add to the body of knowledge regarding the biochemical and microbiological changes related to Cape hake storage, the prediction thereof via contemporary methods and contributing to the safety and effective utilization of this unique and declining South African nutritional resource.