The effect of controlled atmosphere (CA) on the shelf-life of the common mushroom (Agaricus bisporus) was assessed using six parameters correlated with its commerical qualities. Low C02 concentrations (up to 2.5%) reduced brown discolouration compared to the control in air. Higher CO2 concentrations enhanced both internal and external browning. Low O2 concentrations reduced growth of micro-organisms, including pseudomonads. Respiration rate, when the mushrooms are placed again in normal air, is proportional to C 0 2 concentration during storage suggesting that C 0 2 exhibits a phytotoxic effect on mushrooms. A lower mannitol content was noted in mushrooms stored under CA than those stored in air (control). Mushrooms stored in a 5% COz atmosphere for 7 days did not break their veil but their texture was very soft and spongy. Texture losses decreased when C 0 2 concentrations increased.

Until recently, the films used for packaging fresh fruits and vegetables were not permeable enough to balance the high respiration rate of mushrooms. Consequently, modified atmosphere packaging (MAP) in sealed pouches or punnets was not appropriate for this commodity. Four microporous films in oriented polypropylene (OPP) and one film currently used to overwrap mushroom punnets (stretchable PVC) were tested. Mushroom punnets placed into pouches were stored at 4 and 10°C for 8 days. The influence of the modified atmosphere on the marketing quality of pre-packed mushrooms was assessed by measuring the external and internal colour, development stage, firmness and microbial growth. A mathematical model was used to predict the gas composition within the pouches at steady state as a function of the film properties and the characteristics of the plant tissues. The equation calculated from the simplified model shows a linear relationship between the reciprocal of O2 concentration at steady state, (l/x) at 10 and 4°C and the reciprocal of the film permeability, ( 1/Pm02).

The influence of electron beam irradiation on antioxidants present in food packaging materials (OPP and LDPE) was studied. After irradiating the materials at dose levels of 2 , 5 , 1 0 and 25 kGy, w e have shown a partial disappearance of the antioxidant (Irganox 1010, lrganox 1076 and lrgafos 168) and a release of three compounds resulting from the antioxidants degradation related to the irradiation dose. Two of these degradation compounds have been analysed quantitatively: the 2,4-di-tert.-butyl-phenol and the 2,6-di-tert.-butyl-p-benzoquinone. The third compound is a phosphate resulting from a phosphite stabilizer (Irgafos 168).

The influence o f B-ionizing radiation on chemical structure and mass transfer phenomena was studied in the principal flexible food packaging materials (LDPE and OPP). No significant changes were observed in the structure of polymer matrices or in oxygen permeability and global migration after ionizing the materials at dose levels approved for food products (

The long-term influence of electron beam irradiation on food packaging materials (OPP) was studied. After irradiating the material at dose levels of 2, 5 and 10 kGy, w e have shown a partial or complete disappearance of the antioxidant (Irganox 1010 and lrgafos 168) over time and a release of five new compounds resulting from antioxidant degradation. All of these degradation compounds have been identified and quantitatively analysed in relation to post-irradiation time and absorbed dose. These results allow an explanation of the antioxidants' behaviour during storage of the irradiated polypropylene at room temperature.