Doctoral Degrees (Food Science)

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Browsing Doctoral Degrees (Food Science) by Author "Cawthorn, Donna-Maree"

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    Establishment of a genetic database and molecular methods for the identification of fish species available on the South African market
    (Stellenbosch : Stellenbosch University, 2011-12) Cawthorn, Donna-Maree; Witthuhn, R. C.; Steinman, H. A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Consumers have the right to accurate information on the fish products they purchase to enable them to make educated seafood selections that will not endanger their own wellbeing or the wellbeing of the environment. Unfortunately, marine resource scarcity, financial incentives and inadequate or poorly enforced regulations have all promoted the mislabelling of fish species on global markets, the results of which may hold economic, conservation and health consequences. The primary aims of this study were to determine the most commonly available fish species on the South African market, to establish and compare DNA-based methods for the unambiguous identification of these species and to utilise the most applicable methods to evaluate the extent of mislabelling on the local fisheries market. The results from surveys of n = 215 restaurants and n = 200 retail outlets in four South African provinces (Western Cape, Kwa-Zulu Natal, Eastern Cape and Gauteng) indicated that 34 and 70 nominal fish types were available in restaurants and retail outlets, respectively, the most common of which were kingklip, salmon and hake. Over 30% of the fish species being sold were of conservation concern, while several outlets marketed specially-protected, illegal-to-sell species in South Africa. Fish purveyors were poorly equipped to provide information on the identity, origin, production method (farmed/wild) and sustainability of the fish they were selling and the labelling of many packaged fish products was in contravention with South African regulations. Data were published for the first time comparing the efficiency of five methods (urea-SDS-proteinase K, phenol-chloroform, salt extraction, SureFood PREP kit and Wizard Genomic DNA Purification kit) for the extraction of DNA from the muscle tissue of fish species available in South Africa. The SureFood kit was identified as the most suitable method for DNA extraction from fish muscle, extracting significantly (P < 0.05) higher DNA yields than all other methods evaluated and being simple and safe to use. A comprehensive reference library of genetic information was compiled for the first time that contains sufficient DNA sequence data from different mitochondrial DNA loci (16S ribosomal RNA (rRNA), 12S rRNA and cytochrome c oxidase I (COI) genes, as well as the control region) to allow the explicit identification of 53 fish species in South Africa. Although 16S and 12S rRNA gene sequencing allowed the identification of most fish to the genus level, the discrimination of closely-related, congeneric species was problematic when based on these gene regions. Conversely, the vast majority (98%) of fish examined could be readily differentiated by their COI sequences, with only members of the genus Thunnus requiring supplementary control region sequencing for species confirmation. Lastly, sequencing of the COI region was used to show that 9% of fish samples collected from local seafood wholesalers and 31% of samples from retail outlets were mislabelled. This study has established that fish mislabelling is a reality on the South African market and that DNA-based methods should be applied by both industry and regulatory bodies to deter illegal activities and to promote transparency on the domestic fisheries market.