Modified atmosphere packaging (MAP) has been studied as a technique to prolong the shelf-life of fresh vegetables and fruits1)2} . The technique basically expects self-equilibration of the in-package gas composition, which may provide a suitable atmosphere for controlling excess respiration of the fresh produce during
distribution. Since a variety of technical information including permeability of films, respiration rates in a given O2/CO2 atmosphere, respiration quotients, free volume of the package, etc. are required for the proper design of MAP, computer aided simulation is one of the most promising techniques to obtain suitable MAP conditions3)~8). For any MAP design, the exact determination of the in-package concentrations of N2, O2, CO2 and Ar is necessary, because either anaerobic conditions or the presence of excess CO2 results in the development of off-odors, and also the higher concentration of O2 allows for a rapid senescence. Because of the demands for the rapid and simultaneous determination of the in-package gas composition in MAP, gas chromatographical methods have been used. Brenner9) described a combination of silica gel and molecular sieve 5A as parallel columns. Karel et al10). used columns packed with silica gel and a molecular sieve that were connected in series. Recently, Yamashita et al11) used a combination of activated charcoal and a molecular sieve as a parallel column system and calculated the gas composition from the ratio of the peak areas. Aerograph A90 - P36) or Alltech CTR I3)12) have been also used for analyzing the gas composition, while even in some recent papers13)15), the gas analysis procedures are not given in detail. In these columns, Ar is not separated from
O2 and overlaps O2 on gas chromatograms. However the presence of Ar in MAP should be considered for establishing the MAP system because in many cases the critical levels of 0a for providing proper MA conditions are less than 5%. The objectives of this paper are to develop a gas chromatographic method for simul- taneously measuring concentrations (%) of O2, N2t CO2 and Ar in MAP, and to evaluate the gas exchange in MAP of fresh produce on the market or during storage using the method developed.