Optimizing gas mixtures for modified atmosphere packing of fresh king salmon (Oncorhynchus tshawytscha).

摘要

Researchers have evaluated the effect of modified atmosphere packaging (MAP) on the shelf life of fish products. However, there is little published basis for recommended gas mixtures. Most studies have examined the effects of empirical evidence of gas mixes on particular species, but they cannot be used to predict the effect of different gas mixes on shelf life. Further, while the fish:gas ratio has been shown to be a key determinant of bacterial growth under MAP, most studies did not control this parameter. The aim of our research was to optimize gas mixes and fish:gas ratios for the MAP storage of king salmon. Flesh portions from defined fillet positions were placed on drip pads and boxed, giving a standardized nominal volume of 27.4 cm3 and an exposed surface area of 14.4 cm2. Each sample was placed in a foil barrier bag containing an oxygen absorber. Controlled volumes (0-100 cm3) of CO2 or 100 cm3 of a 40:60 mixture of CO2:N2 were then hand-injected through a septa. Bags were stored in melting ice (0+or-0.05 degrees C) and analysed after 0, 8, 22 and 90 days for headspace CO2 and O2, EH, fish freshness meter (Distell, West Lothian, Scotland) reading, drip loss, texture, raw and cooked sensory characteristics, microbial numbers, bacterial flora composition, total volatile base nitrogen (TVBN) and ATP derivatives. High CO2 levels reduced bacterial counts, but resulted in poor cooked sensory characteristics due to carbonated flavour. We calculated the threshold level of CO2 at which this could be detected by our trained panel. We also determined the solubility of CO2 in salmon flesh and calculated Henry's constant to resolve the relationship between gas mixes and the fish:gas ratio. We now have the basis of a simple mathematical model optimizing these to give maximum shelf life and sensory acceptability.