Browsing by Author "Bosch, Adina Cornelia"

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    Investigation of the chemical composition and nutritional value of smoothhound shark (Mustelus mustelus) meat
    (Stellenbosch : Stellenbosch University, 2012-03) Bosch, Adina Cornelia; Hoffman, Louwrens C.; Sigge, G. O.; Kerwath, Sven; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: The aim of this study was to determine the proximate composition of five individual body sites of the Mustelus mustelus shark in order to evaluate the cross carcass variation of the individual proximate components (moisture, protein, lipid, ash) of the meat. This variation was determined in order to find a representative sample of the edible part of the shark (fillet and body flap). Secondly, this sample representing the entire shark fillet was used to investigate the endogenous factors (gender, size and life cycle stage) and their effects on the individual proximate components and other meat components (amino acids, fatty acids, minerals, histamine and mercury contents). Finally, all this data was combined to describe the average chemical composition and nutritional value of M. mustelus meat. None of the proximate components showed any variation between the different fillet positions. This indicated that the fillet is homogenous and samples for chemical analyses can be taken anywhere on the fillet as representative of the entire fillet. It was found that all three main effects (gender, size and life cycle stage) did not have major influences on most of the components of the chemical composition of M. mustelus meat analysed. Higher fatty acid levels (SFA, MUFA and PUFA) were observed in large females than in large males as well as in non-pregnant large females compared to pregnant large females. According to statistical analysis, large males had higher total mercury levels than large females. The only component affected by size variation was the fatty acids, showing a trend to decrease in quantity before maturity was reached. Variation due to life cycle stages was mostly evident in the fatty acid component with some small effects on two mineral components, aluminium and copper, which had slightly higher levels in pregnant large females than in non-pregnant large females. M. mustelus meat has an average proximate composition of 75% moisture, 23% protein, 1.6% lipids and 1.4% ash (weight per wet weight). The protein is, however, an over-estimation of the true protein value as the meat contains significant amounts of non-protein nitrogen (NPN) in the form of urea which contributes to the N concentration. M. mustelus meat is a good source of some essential amino acids, especially lysine and threonine (78% of the daily requirements for an adult in a 100g portion), but low in minerals. The meat has a healthy lipid content with a good ratio (>0.45) of PUFA:SFA (0.83) as well as a healthy (<4) n-6:n-3 fatty acid ratio of 0.39. The histamine content was very low or not detectable but some samples contained total mercury values above the maximum safe limit. Although further research is needed for some meat components, these results are a valuable contribution to the new South African Food Composition Tables being compiled.
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    Status of mercury and other heavy metals in South African marine fish species
    (Stellenbosch : Stellenbosch University, 2015-12) Bosch, Adina Cornelia; Hoffman, Louwrens C.; Sigge, G. O.; Kerwath, Sven E.; O’Neill, Bernadette; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Fish is an important food source in South Africa as it is globally, thus the importance of determining and monitoring its safety in terms of metal contaminants and consumer safety. Effective methodology for analysing total metal concentrations and toxic metal components together with representative sampling protocol for sampling individual fish and larger catches are therefore required for accurate assessment of meat safety. Both inductively coupled plasma mass spectrometry (ICP-MS) and high pressure liquid chromatography coupled to ICP-MS was validated as effective methods for accurately determining concentrations of total metals and individual Hg species, respectively. Consequently, it was found that total mercury loads in fish meat consisted mainly of toxic methylmercury (MeHg) components with a minor addition of an inorganic Hg (iHg) component and ethylmercury concentrations being negligible. This proportion of MeHg to iHg varied between muscle types in yellowfin tuna (Thunnus albacares), with higher iHg concentrations in dark muscle than in white muscle, whereas the toxic MeHg concentrations did not vary across the carcass. The MeHg to tHg relationship was caused to vary with variation in fish weight, being described by the following prediction model: 𝑐𝑀𝑒𝐻𝑔=0.073+1.365∙𝑐𝑡𝐻𝑔−0.008∙𝑤; taking into account fish weight as covariate. For the eight other fish species studied [blacktail (Diplodus sargus capensis), hottentot (Pachymetopon blochii), yellowtail (Seriola lalandi), snoek (Thyrsites atun), blue shark (Prionace glauca), shortfin mako (Isurus oxyrinchus), soupfin (Galeorhinus galeus) and smoothhound (Mustelus mustelus)], the relationships between MeHg and tHg were constant even with varying fish sizes as iHg components were considered an insignificant portion of tHg (ctHg = cMeHg). The tHg measurements could therefore be used as accurate indicators of MeHg concentrations without requiring addition speciation analyses. Sampling from the cephalic region of the dorsal white muscle tissue proves representative of the entire edible portions (white muscle) of larger fish (tuna and sharks spp.) for determining both total metal concentrations and toxic Hg components. Where Hg concentrations are positively correlated to fish size (yellowfin tuna, yellowtail and soupfin), subsamples should include individuals representing the entire size range present per catch. A summary of metal concentrations in all eight species studied indicate that Hg is the main metal of concern where a single portion of certain fish (yellowfin tuna, shortfin mako, soupfin and smoothhound shark) consumed per week could exceed regulatory limits for safe Hg intake, whereas other fish species (hottentot) could be consumed daily without concern of Hg toxicity. Information provided by this study will prove useful to both the fishing and processing industry as well as to health authorities providing information for dietary exposure assessments.