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Anlaug Ådland Hansen defended her doctoral thesis on December 12, 2008
Ane Gro Siri SkjelfjordReduced headspace volume of modified atmosphere packaged fresh salmon (Salmo salar L.) and cod (Gadus morhua L.) by use of a carbon dioxide emitter
Modified atmosphere packaging (MAP) is a method for preserving food quality. The atmosphere surrounding the product is replaced by adding a gas mixture before sealing the package. To obtain an optimal delayed bacterial growth of MAP seafood products, a certain partial pressure of CO2 is required. The initial gas to product volume ratio should be about 3/1 to ensure sufficient CO2 in headspace. This is space demanding. Therefore, a packaging technology by use of a CO2 emitter was developed to achieve reduced headspace in MAP.
The main objective of this study was to investigate the possibility of reducing headspace of traditional MAP by use of a CO2 emitter without compromising quality and shelf life of fresh fish products. Farmed pre-rigor filleted Atlantic cod (Gadus morhua L.) and Atlantic salmon (Salmo salar L.) were studied during 0-2°C storage for 3-4 weeks packaged with 60% CO2/40% O2 and 60% CO2/40% N2, respectively. Additionally, MAP was compared to packaging in air and in vacuum. Superchilled salmon packaged in modified atmosphere with a CO2 emitter during 0°C storage was also investigated. Quality measurements were performed during storage, to evaluate quality development and to find an approximate shelf life of the fillet pieces.
The results show that MAP with a CO2 emitter inhibited bacterial growth as good as, or better than traditional MAP with a higher headspace volume (gas/product volume ratio of 1/1 or 1/2 vs. 4/1 or 3/1). The shelf life of the MAP salmon and cod fillets was 14-21 days and 18-22 days, respectively (total bacterial count above log 6 cfu/g). Vacuum packaged fillets had a shelf life of 10-11 days. The pH values of fillets in the MAP with a CO2 emitter were similar or lower compared with traditional MAP. The results therefore indicate that the CO2 emitter compensated for the reduced headspace and that similar or higher CO2 absorption in the fish muscle was facilitated.
Liquid losses, colour, texture and odour were similar for the two MAP methods. Vacuum packaged salmon tended to be firmer compared with the MAP salmon, but the redness was lower ( 15 days) and the liquid loss was higher ( 4 days). The vacuum packaged cod tended to be whiter ( 15 days), whereas the TMA content was higher. For both species, development of negative odours developed earlier in vacuum packaged fillets compared to MAP fillets. When combining superchilling as pre-treatment with MAP the firmness at the surface layer of the fillets was lower and the liquid loss was higher. The superchilling treatment resulted in lower bacterial counts of bottom fillets in MAP compared to corresponding traditional chilled MAP fillets. An improved superchilling method, preventing liquid loss and softening of texture, combined with MAP with a CO2emitter may ensure high quality pre-rigor fillets with a prolonged shelf life.
The main conclusion is that MAP with a CO2 emitter can reduce the headspace volume without compromising quality and shelf life. Reduced headspace makes space for at least 50% more fish during transport, storage and in the food store shelves. Additionally, the required packaging materials and use of packaging gases are reduced relative to amount of fish. Hence, using a CO2 emitter in MAP fish may contribute to economical and environmental benefits.
Oppdatert: 07.01.09
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