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.
The results of a research project (EU AIR Research Programme CT94-1025) aimed to introduce control of migration into good manufacturing practice and into enforcement work are reported. Representative polymer classes were defined on the basis of chemical structure, technological function, migration behaviour and market share. These classes were characterized by analytical methods. Analytical techniques were investigated for identification of potential migrants. High-temperature gas chromatography was shown to be a powerful method and 1H-magnetic resonance provided a convenient fingerprint of plastic materials. Volatile compounds were characterized by headspace techniques, where it was shown to be essential to differentiate volatile compounds desorbed from those generated during the thermal desorption itself. For metal trace analysis, microwave mineralization followed by atomic absorption was employed. These different techniques were introduced into a systematic testing scheme that is envisaged as being suitable both for industrial control and for enforcement laboratories. Guidelines will be proposed in the second part of this paper.
High-level ab initio calculations were performed on a two-center three-electron (2c−3e) bond between
formaldehyde and the radical cation of ammonia. The stability of the resulting complex is found to be 21.8
kcal/mol, only 2.2 kcal/mol higher than the hydrogen bonded complex of the same species. Upon replacing
the formaldehyde by thioformaldehyde (H2CS), the 2c−3e complex is found to be 20 kcal/mol more stable
than the corresponding hydrogen bonded complex. The imine group is also studied via the H2CNH system.
This compound exhibits a larger 2c−3e bond energy, 32.0 kcal/mol, but this is still 8.8 kcal/mol higher in
energy than the hydrogen bonded complex. This is the first theoretical evidence of a possible 2c−3e complex
involving organic unsaturated systems.
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