Abstract
Fish muscle proteins undergo complex physicochemical changes during frozen storage which result in the toughening of muscle and unpalatability. The aim of this thesis was to examine the aggregation of fish proteins as a result of frozen storage, in particular the effect of formaldehyde on proteins. Atlantic cod (Gadus morhua) and Namibian hake (Merluccius capensis and Merluccius paradoxus) muscle proteins were characterised and differentiated by electrophoretic and immunological approaches. The nature of the chemical bonds involved was elucidated by the use of reagents capable of breaking the non-covalent and covalent bonds. Conformational changes of the protein were investigated by both immunological and chemical techniques. Structural and textural changes on frozen storage in the presence of formaldehyde were examined by microscopic, deformation-compression analysis and dynamic mechanical testing. In addition, a lysosomal enzyme (Trimethylamine oxidase) which is responsible for the toughening of gadoid fish muscle during storage was characterised. Electrophoretic separation of the sarcoplasmic proteins from Merluccius capensis and Merluccius paradoxus confirmed the biological closeness of the two species. A 19kD protein band from M. capensis, excised from the SDS gel, was used for the production of polyclonal antibodies as analysed by an Enzyme Linked Immunosorbent Assay (ELISA). Formaldehyde and frozen storage augmented the extent of protein insolubilisation. The results of this study showed conclusively that formaldehyde is only one of many factors involved in the denaturation of fish proteins during frozen storage. List of objectives of the project. The objectives were: to characterise the fish muscle proteins and differentiate between the Namibian hake species Merluccius capensis and Merluccius paradoxus; to elucidate the chemical aspects related to solubility and foaming of fish muscle proteins in the presence of formaldehyde; to assess structural and textural changes in frozen and formaldehyde treated fish proteins by microscopy and viscoelastic measurements; to examine the changes in sulphydryl, disulphide and hydrophobic groups during frozen storage; to examine the changes in sulphydryl, disulphide and hydrophobic groups in the presence of formaldehyde; to monitor the degradation of trimethylamine oxide, formaldehyde and trimethylamine during frozen, storage of fish; and to characterise the enzyme TMAOase and to assess the effect of inhibitors. (Abstract shortened by ProQuest.).