Tengiliður
Kolbrún Sveinsdóttir
Verkefnastjóri
kolbrun.sveinsdottir@matis.is
The effect of cooling methods at processing and use of gel-packs on storage life of cod (Gadus morhua) loins – Effect of transport via air and sea on temperature control and retail-packaging on cod deterioration
Tilgangur tilraunanna var að kanna áhrif mismunandi kælingar við vinnslu og hitasveiflna í flutningi með og án kælimottu á geymsluþol þorskhnakka. Í vinnslu var borið saman að nota enga forkælingu fyrir flökun, vökvakælingu og roðkælingu (CBC) sem alltaf er með vökvakælingu. Áhrif hitasveiflna þar sem líkt var eftir í hitabreytingum í flutningi (RTS) voru borin saman við geymslu við stöðugt hitastig (-1 °C). Einnig voru metin áhrif þess að nota kælimottu í geymslu og flutningi. Sýni voru gæðametin með skynmati, örveru- og efnamælingum. Fylgst var með hitastigi með hitasíritum. Roðkældir þorskhnakkar í frauðplastkössum voru fluttir til Bremerhaven með flugi og skipi þar sem þeim var endurpakkað í loft og loftskiptar pakkningar (MAP) og þær geymdar við 1 °C. Gerðar voru efna- og örverumælingar til að fylgjast með gæðabreytingum. Hitastig roðkældra hnakka var lægra en hinna fyrstu 2 daga tilraunarinnar. Kælimotturnar höfðu ákveðin áhrif til lækkunar hitastigs þegar hitasveiflur voru í ferlinu og lægri hiti hélst gegnum allan geymslutímann. Samt sem áður hafði notkunin ekki áhrif á lengd ferskleikatíma eða geymsluþols samkvæmt skynmati. Örverufjöldi var heldur lægri ef hitasveiflur urðu í ferlinum en lítill munur var við stöðugt hitastig. Geymsla við stöðugt, lágt hitastig (-1 °C) lengdi geymsluþol um ca. 3 daga samkvæmt skynmati og var það í samræmi við örverutalningar og mælingar á TVB-N og TMA. Í tilraunum í Bremerhaven kom fram að örverufjöldi var yfirleitt lægri þegar notaðar voru loftskiptar umbúðir í samanburði við fisk í lofti. Þetta var sérstaklega áberandi í flugfiskinum. Fiskurinn sem fluttur var með skipi geymdist samt jafn lengi og fiskurinn sem fluttur var með flugi. Þetta orsakast af því að flugfiskurinn varð fyrir meiri hitasveiflum í flutningi og yfirborðshiti hans mældist 4 °C við komuna til Bremerhaven. Flutningstími með skipi var miklu lengri (+48 klst) en yfirborðshiti mældist undir 2 °C við móttöku. Notkun kælimotta hafði lítil áhrif á hitastigið í flutningi en samt sem áður var yfirborðshiti aðeins lægri í fiski með kælimottum við komuna til Bremerhaven bæði með flugi og skipi.
The main aim of the experiment was to investigate the effects of different cooling techniques during processing and temperature fluctuations during transport on the storage life of cod loins with and without gel packs. The following cooling techniques were studied: combined blast and contact (CBC) cooling (with liquid cooling prior to the CBC cooling), only liquid cooling and where no special cooling was used prior to deskinning and trimming. The effect of real temperature simulation (RTS) during storage was compared to a steady storage temperature of -1 °C. The samples were analysed with sensory, microbial and chemical methods. The temperature was monitored from packaging using temperature loggers. CBC cooled loins were transported to Bremerhaven via air and ship freight after packaging in EPS boxes. The fish was repacked in air and modified atmosphere and stored at 1 °C. Deteriorative changes were evaluated by microbial and chemical indicators. CBC cooling resulted in a lower temperature profile the first two days of the experiment. The use of gel packs lowered somewhat the temperature increase in the products when RTS was applied and lower temperature was maintained during the entire storage period. According to sensory evaluation, the use of gel packs did not result in prolonged freshness period or shelf life. According to microbial and chemical analysis no marked difference was seen whether gel packs were used or not in groups stored at a steady temperature. However, microbial counts were somewhat lower and slower formation of TVB-N and TMA occurred in RTS groups where gel packs were used compared to no gel packs. Storage at a steady -1 °C resulted in prolonged shelf life of three days according to sensory evaluation. This was confirmed by microbial and chemical analysis as lower microbial counts, TVB-N and TMA values were generally obtained in the steady temperature group than in the group receiving the RTS treatment. The storage studies carried out at Bremerhaven on modified atmosphere vs. air packed loins showed generally lower microbial counts, especially in the air transported fish. Deterioration process of air and sea freight fish was however similar. Re-packaging of sea freight fish at a later stage did not significantly affect its deteriorative process compared to re-packed air freight fish. This might be due to the fact, that the air freight fish was subject to high temperatures during transport and surface temperature reached over 4 °C. The sea freight fish had a much longer transport phase, but arrived with surface temperatures below 2° C. This shows that not only the time of re-packaging but also the temperature profile during transport are important factors influencing the deteriorative process and shelf life. Gel packs did not have significant cooling effect in this experiment. However the surface temperature in boxes with a gel pack was slightly lower than in boxes without a gel pack independently of transport mode used.