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The effect of carbon monoxide on the colour stability and quality of yellowfin tuna (Thunnus Albacares) muscle

Neethling, Nikki E. (2013-03)

Thesis (MSc Food Sc )--Stellenbosch University, 2013.

Thesis

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.

AFRIKAANSE OPSOMMING: Prosesseerders staar die probleem om geelvintuna se raklewe te verleng en terselfdertyd die helder rooi kleur van die vleis te behou, in die gesig. Verskeie aanvaarde metodes, bv. die vries en vakuumverpakking van vleis teen ultra-lae temperature, wat gedurende die behandeling van ander soorte vleis en vis die gewenste uitwerking het, het nie die gewenste uitwerking op tuna nie. Beide laasgenoemde metodes veroorsaak ongewenste kleurverandering van die vleis. ‘n Alternatiewe metode is die gebruik van koolstofmonoksied (CO) behandeling wat tunaspier met 'n wenslike kersie-rooi kleur wat stabiel tydens bevriesing en vakuumverpakking is tot gevolg het. Dit word tipies in samewerking met bevriesing en vakuumverpakking gebruik en kan as 'n enkele gas (100% CO) of as deel van 'n mengsel van gasse by wisselende konsentrasies toegedien word. Ander voordele met die gebruik van CO behandeling sluit die potensiële inhibering van proteïen en lipied oksidasie in wat kan lei tot die verlenging van rakleeftyd. Die gebruik van CO met tuna word egter gekritiseer aangesien dit bederf aanwysers, soos verkleuring, kan verbloem wat misleidend vir verbruikers kan wees. Twee loodstudies het gewys dat tuna vir 150 min teen 3 bar druk behandel moet word (+CO) om die gewenste ontwikkeling van oppervlak kleur en kleur penetrasie te bekom. As kontrole medium was onbehandelde toetsmonsters gebruik (-CO). In ooreenstemming met industrie standaarde was die tuna aan aerobiese (toegedraai) (OP) sowel as anaerobiese (OI) toestande teen óf een (Fx1) óf twee (Fx2) vries/ontdooi siklusse blootgestel. Daar was gevind dat CO behandeling die oppervlakkleur van die tuna spiere gedurende die vries sowel as ontdooi siklusse bevorder, gehandhaaf en gestabiliseer het. Die karboksimioglobien van die OP monsters het egter vinnig tot metmioglobien geoksideer en ‘n ongewenste bruin verkleuring tot gevolg gehad. Die OI monsters daarenteen het hul kleur gedurende die duur van die raklewe toets behou. Die verhoogde skade wat deur die tweede vries/ontdooi siklus teweeggebring was, was nie kennelik sigbaar in die OP +CO behandelings nie, maar die effek was tydens die OI +CO behandelings waargeneem. Die CO behandelings het op nóg die lipied nóg die proteïen oksidasie ‘n uitwerking gehad. Die aantal vries/ontdooi siklusse het ook geen effek op die lipied oksidasie gehad nie, maar het die proteïen oksidasie tot so ‘n mate versnel dat die karboniele wat gemeet was gereageer het met ander biologiese komponente en nie verder waargeneem kon word nie. Die verpakking het op beide die proteïen sowel as lipied oksidasie ‘n effek gehad, maar ‘n verlaagde lipied oksidasie en gestremde proteïen oksidasie is waargeneem tydens OI behandelings. ‘n Korrelasie tussen mioglobien oksidasie en proteïen oksidasie was in die tuna spiere gedurende al die behandelings waargeneem. In die OI +CO monsters het die *a waardes egter hoog gebly selfs terwyl die b* sowel as TBARS waardes gestyg het. Die CO behandeling het dus die sigbare aanwyser (verbruining) van lipied oksidasie verskans.

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