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The effect of different precooling media during processing and cooling techniques during packaging of cod (Gadus morhua) fillets

Author(s):

Björn Margeirsson, Hannes Magnússon, Kolbrún Sveinsdóttir, Kristín Líf Valtýsdóttir, Eyjólfur Reynisson, Sigurjón Arason

Funded by:

AVS Fund of Ministry of Fisheries in Iceland, The Technology Development Fund at the Icelandic Centre for Research, University of Iceland Research Fund

Contact

Kolbrún Sveinsdóttir

Project Manager

kolbrun.sveinsdottir@matis.is

The effect of different precooling media during processing and cooling techniques during packaging of cod (Gadus morhua) fillets

Tilgangur tilraunanna var að kanna áhrif mismunandi kælimiðla við forkælingu fyrir pökkun á hitastýringu, gæði og geymsluþol þorskflaka. Eftirfarandi kælimiðlar voru kannaðir og bornir saman við enga sérstaka forkælingu fyrir pökkun:

  1. pækill með lágu saltinnihaldi, 2) krapaís með lágu saltinnihaldi.

Auk þess voru könnuð áhrif þess að nota annars vegar ísmottur og hins vegar þurrís við geymslu flakanna. Fylgst var með breytingum á hitastigi með hitanemum á öllum stigum. Sýni voru gæðametin með skynmati, örveru- og efnamælingum í allt að 13 daga frá vinnslu og pökkun (16 daga frá veiði). Flökin voru geymd við ofurkældar aðstæður (undir 0 °C) mestan hluta geymslutímans. Lægra hitastig krapaíss en pækils leiddi til lægra hitastigs flaka við pökkun auk þess sem hiti vökvapækilsins reyndist hækka hratt þegar hlé var gert á vinnslu. Mismunandi meðhöndlun leiddi til sambærilegs ferskleikatíma samkvæmt skynmati. Hins vegar reyndist notkun vökvapækils við forkælingu fyrir pökkun leiða til 1 – 2 daga skemmra geymsluþols samanborið við enga forkælingu eða forkælingu með krapaís. Rekja má ástæður þessa til þess að pækillinn innihélt töluvert magn örvera, m.a. H2S-myndandi gerla sem eru virkir framleiðendur á trímetýlamíni (TMA). Samanburður á vökvakældu flökunum sýndi að notkun á þurrís lengdi geymsluþol um 1 dag í samanburði við ísmottur. Niðurstöður örveru- og efnamælinga voru í samræmi við þessar niðurstöður.

The aim of the experiment was to investigate effects of two cooling media during precooling at processing on temperature control, quality and storage life of cod fillets. The two cooling media compared to no special precooling during processing (NC) were: 1) liquid brine (LC) and 2) slurry ice (SIC). In addition, the influence of using either dry ice or ice packs during storage was studied. The samples were kept at superchilled conditions during most of the trial. The environmental and product temperature history of each group was studied using temperature monitors. The samples were analysed with sensory evaluation, microbial and chemical methods for up to sixteen days from catch (thirteen days from processing). Lower temperature of the slurry ice than the liquid brine resulted in lower fillet temperature at packaging and the liquid brine temperature increased rapidly during a processing break, which seems to be a weakness of the liquid brine tank. Results from sensory, microbial and chemical analysis all showed that immersing the skinless cod fillets in liquid cooling brine prior to packaging resulted in one to two days reduction of shelf life in comparison with fillets that were not immersed in liquid brine (no cooling) or in slurry ice. This could be attributed to the fact that the cooling brine carried considerable amounts of microbes including H2Sproducing bacteria which are active producers of trimethylamine (TMA). Comparison of the groups receiving liquid cooling showed that dry ice appeared to extend the shelf life of one day as compared to ice packs. The length of the freshness period was, however, similar in all experimental groups according to sensory evaluation. These results were confirmed by total volatile bases (TVB-N) and TMA analysis and microbial counts.

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