Oxygen transmission Ethylene vinyl alcohol Microwave processing Retort

teril tion en nsm a 7-layer co-extruded structure of PP/tie/Nylon 6/EVOH/Nylon 6/tie/PP. The films were used as lidstocks requi proces mmon films of different mol % ethylene contents at RH above 75–80% measured at 15, 20, and 35 C. Muramatsu et al. (2003) reported one hundred times increase in oxygen permeability as RH in-creased from 0 % to 90 % for EVOH film of 29 mol % ethylene mea-sured at 20 C. Oxygen permeation into food packages may cause rancidity and other oxidative degradation reactions in lipid-con-taining foods resulting in quality losses. Undesirable aroma com-pounds may also diffuse into a package with a compromised the long exposure to water at sterilization temperatures causes se-vere losses to the barrier properties of EVOH containing films and makes them unsuitable for conventionally retorted foods. On the other hand, microwave (MW) heating generates thermal energy within the food, thus sharply reducing the time to raise the product temperature required to achieve thermal lethality to target bacte-ria (Bengtsson and Ohlsson, 1974). Guan et al. (2002) reported that it took only 8 min to raise the temperature of a macaroni and cheese product to 127 C in a microwave-circulated water combi-nation heating system, while it took 40 min for conventional hot water retort for the same sized trays. Guan et al. (2002) furthe