This thesis is concerned with identifying some of the factors which affect the flesh quality of Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). The flesh of any food animal is of utmost importance. Much work has been carried out on the flesh of land animals, but comparatively little is known about the factors which affect the quality of fish flesh. Salmonids have been farmed for a relatively short period of time, but great advances have been made in the techniques for their rearing. Now that the fish can be grown easily, more information is required on the factors which affect their fish quality in order to produce a consistent product. Fish fed a high oil diet have a significantly higher level of flesh lipid than fish of the same size fed a low oil diet (uncertainty p < 0.001). This has implications for the eating quality of the fish as many attributes of the eating quality of smoked salmon are significantly affected by the flesh lipid content. The flesh texture becomes softer and the flavours stronger, apart from salty flavour which decreases dramatically with increasing lipid (p < 0.001). The general effect of increasing lipid is to increase the perception of overall flavour and the overall liking of the product, as judged by the ten person trained taste panel. In contrast there are much fewer effects of the lipid content on cooked salmon and there are no effects on the overall flavour or overall liking (p > 0.05). The colour of the flesh is of great importance to the flesh quality of salmonids. Stress at slaughter is known to affect the muscle chemistry post-slaughter. This work shows that reducing stress at slaughter significantly increases the colour of the flesh, resulting in lower lightness (p < 0.05), an increased red hue (p < 0.05) and reduced opacity (p < 0.05) as measured using the CElab 1976 method. The change in colour is also shown by an increased Roche colour card score using the subjective colour card score (p < 0.05). Reduced stress at slaughter is also found to result in a longer time to the onset of rigor (p < 0.001) and a reduced susceptibility to gaping of the flesh (p < 0.01). Current commercial 'best practice' methods of slaughter were found to be highly stressful to the fish. The red colour of the flesh has been previously reported to reduce during storage, but this research found no changes in the level of the pigment astaxanthin during 12 days of storage of salmon fillets on ice. No effects of the level of astaxanthin or the antioxidant vitamins ascorbic acid and a-tocopherol at slaughter were found on the eating quality of the cooked flesh, either fresh or after 12 days storage on ice. However, many other attributes of the eating quality were significantly affected during the storage period, with increases in many flavours and textures associated with "off' fish. This translated into a significant reduction in the expression of overall liking by the trained taste panel (p < 0.001). The research for this thesis has shown areas where further research is required to investigate factors having effects on flesh quality. The most important of these new areas is the effect of stress level at slaughter on flesh quality. There is a strong possibility that stress at this point has wide ranging effects, the results of which may actually confound improvements introduced into in other areas of quality control unless they are eliminated from salmon farming practices.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:245743 |
| Date | January 1998 |
| Creators | Robb, David Henry Francis |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1983/c474b238-aff0-4c37-96af-e223c441f6eb |
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