Combining MAP with other preservation techniques 295 found in chilled retail counters. Sikorski and Sun(1994) found that super- chilling can store enough refrigeration capacity to keep a core temperature <ooC during the first three weeks of chilled storage. a shelf-life extension of seven days has been obtained for super-chilled fish when compared to traditional ice stored fish of the same type (Leblanc and Leblanc, 1992). Untreated salmon steaks in MA, and partial frozen salmon steaks in MA, had an acceptable microbiological quality of 22 days at OoC, but were rejected by odour after 17 days. Salmon steaks in air had and acceptable microbiological quality for only eight days(Rosnes et al., 2001). MAP is also being used to package products for frozen storage. The reasoning behind the use of MAP for ready-to-eat products is that they can be distributed frozen, then thawed and sold as chilled products but with an extended shelf-life(Morris, 1989) 14.3.2 radiation The attraction of combining irradiation with MAP is that the modified atmospheres are not lethal to spoilage organisms and pathogens. The possibility exists, therefore, of using irradiation below the threshold dose, i.e., the level at which spoilage organisms and pathogens are killed and below the level where undesirable organoleptic changes are introduced, in order to enhance the attractiveness of MAP. The effects of MAP/irradiation on sensory properties, and its effect upon depletion of vitamin content during storage, compared to untreated items. have been examined in detail. Studies on the effects of maP/ irradiation methods on nutritional quality showed that the deleterious effects of irradiation on vitamins can be removed by modify ing storage atmospheres (Robins, 1991). For a radiation dose of 0. 25 kGy and in an air atmosphere, 60% of the thiamine content was lost over the storage period, compared to a minimal loss in the non-irradiated control over the same period. The loss of a-tocopherol exposed to l kGy irradiation, was some 50% over this period, compared to a similar minimal loss in the non-irradiated control sample. In both cases there were much reduced loss rates in N2 atmospheres, which demonstrated that the ffects of irradiation on these vitamins could be removed by modifying storage atmospheres The growth rate of surviving microorganisms was measured as a function of atmospheric composition for the irradiated and non-irradiated food samples, and the optimum lethal atmospheres were found to range from CO2/N2: 25/75 to CO,/N2: 50/50. Tests at 10c showed a similar trend, although the effectiveness of high concentrations of CO2 was reduced. The major surviving organisms even in the irradiated packs were lactobacilli, in accordance with general expectations on their resistance to radiation A series of experiments on MAP/irradiation combination, for use with chicken and pork products, with the goal of optimising sensory quality have shown that each particular food item requires careful evaluation and that generalisation can lead to incorrect and inappropriate specifications for optimum storage. However, as one of several different treatment combinations aimed atfound in chilled retail counters. Sikorski and Sun (1994) found that super￾chilling can store enough refrigeration capacity to keep a core temperature < 0ºC during the first three weeks of chilled storage. A shelf-life extension of seven days has been obtained for super-chilled fish when compared to traditional ice stored fish of the same type (Leblanc and Leblanc, 1992). Untreated salmon steaks in MA, and partial frozen salmon steaks in MA, had an acceptable microbiological quality of 22 days at 0ºC, but were rejected by odour after 17 days. Salmon steaks in air had and acceptable microbiological quality for only eight days (Rosnes et al., 2001). MAP is also being used to package products for frozen storage. The reasoning behind the use of MAP for ready-to-eat products is that they can be distributed frozen, then thawed and sold as chilled products but with an extended shelf-life (Morris, 1989). 14.3.2 Irradiation The attraction of combining irradiation with MAP is that the modified atmospheres are not lethal to spoilage organisms and pathogens. The possibility exists, therefore, of using irradiation below the ‘threshold’ dose, i.e., the level at which spoilage organisms and pathogens are killed and below the level where undesirable organoleptic changes are introduced, in order to enhance the attractiveness of MAP. The effects of MAP/irradiation on sensory properties, and its effect upon depletion of vitamin content during storage, compared to untreated items, have been examined in detail. Studies on the effects of MAP/ irradiation methods on nutritional quality showed that the deleterious effects of irradiation on vitamins can be removed by modifying storage atmospheres (Robins, 1991). For a radiation dose of 0.25 kGy and in an air atmosphere, 60% of the thiamine content was lost over the storage period, compared to a minimal loss in the non-irradiated control over the same period. The loss of -tocopherol, exposed to 1 kGy irradiation, was some 50% over this period, compared to a similar minimal loss in the non-irradiated control sample. In both cases there were much reduced loss rates in N2 atmospheres, which demonstrated that the effects of irradiation on these vitamins could be removed by modifying storage atmospheres. The growth rate of surviving microorganisms was measured as a function of atmospheric composition for the irradiated and non-irradiated food samples, and the optimum lethal atmospheres were found to range from CO2/N2 : 25/75 to CO2/N2 : 50/50. Tests at 10ºC showed a similar trend, although the effectiveness of high concentrations of CO2 was reduced. The major surviving organisms even in the irradiated packs were lactobacilli, in accordance with general expectations on their resistance to radiation. A series of experiments on MAP/irradiation combination, for use with chicken and pork products, with the goal of optimising sensory quality have shown that each particular food item requires careful evaluation and that generalisation can lead to incorrect and inappropriate specifications for optimum storage. However, as one of several different treatment combinations aimed at Combining MAP with other preservation techniques 295