Browsing by Author "Neethling, Nikki E."
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- ItemThe effect of carbon monoxide on the colour stability and quality of yellowfin tuna (Thunnus Albacares) muscle(Stellenbosch : Stellenbosch University, 2013-03) Neethling, Nikki E.; Hoffman, Louwrens C.; Britz, T. R.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Processors face the problem of extending the shelf-life of yellowfin tuna, while still maintaining the desirable bright red colour. Methods which have commonly been applied to meats and fish for shelf-life extension, such as ultra-low temperature freezing and vacuum packaging, have proved ineffective for tuna as these methods result in undesirable colour changes. Another method is the use of a carbon monoxide (CO) treatment, which results in tuna muscle with a desirable cherry-red colour that is stable during freezing and vacuum packaging. It is generally used in conjunction with freezing and vacuum packaging and can be used as a single gas (100% CO) or at varying concentrations in a mixture of gases. Other benefits of the use of CO include the potential inhibition of protein and lipid oxidation which would result in shelf-life extension. Its use with tuna has been criticised as it could mask spoilage indicators such as discolouration which could be misleading to consumers. Two pilot studies established that the tuna would be treated (+CO) for 150 min at 3 bar pressure to attain the desired surface colour development and colour penetration. Untreated samples were used as a control (-CO). In accordance to industry practices, the tuna was also subjected to both aerobic (overwrap) (OP) and anaerobic (OI) conditions and either one (Fx1) or two (Fx2) freeze/thaw cycles. It was found that the CO treatment did enhance, maintain and stabilise the surface colour of the tuna muscle during freezing and thawing. The carboxymyoglobin of the OP samples, however, rapidly oxidised to metmyoglobin, resulting in an undesirable brown discolouration. The OI samples maintained the colour throughout the shelf-life trial. The enhanced damage caused by the second freeze/thaw cycle was not apparent in the OP +CO treatments but the effect was seen in the OI +CO treatments. The CO treatment had no effect on either the lipid or protein oxidation. The number of freeze/thaw cycles also had no effect on the lipid oxidation but accelerated the protein oxidation to such an extent that the carbonyls being measured had reacted with other biological constituents and could no longer be detected. The packaging had an effect on both the protein and lipid oxidation with less lipid oxidation and retarded protein oxidation being observed in the OI treatments. A correlation was observed between myoglobin oxidation and protein oxidation in the tuna muscle with all the treatments. In the OI +CO samples, however, the a* values remained high even as the b* values and TBARS values increased. Thus the CO treatment of the tuna masked the visible indicator (browning) of lipid oxidation. It was concluded that overall the OI +CO Fx1 treatment resulted in the best quality product with regards to colour stability, colour maintenance, and lipid and protein oxidation. The results from this study reiterated the concerns regarding the use of CO with tuna as it can mask visible spoilage indicators which raise food safety concerns.