| Summary: | The occurrence of total gas pressure gradients, which act as a driving
force for the mass transport of fluids, may be common phenomena in plant
organs. A gas-exchange system was devised to characterize changes in CO₂
emission rates of greenhouse tomato fruit (Lycopersicon esculentum L.
Dombito), greenhouse green bell pepper fruit (Capsicum annum L. Doria),
slicing cucumber fruit (Cucumis sativa L. Straight Eight and Sweet Success) and
jumbo yellow onion bulbs (Allium cepa L.) in response to the imposition of total
gas pressure gradients. Cyclical variations in atmospheric pressure induced
significantly higher rates of gas exchange in peppers and onions but not in
tomatoes and cucumbers. Oxygen concentration significantly affected carbon
dioxide efflux rates in onions subjected to variable pressures. Temperature had
no significant effect on relative efflux rates in any of the plant organs used in this
study. Duration of the interval between varying pressure treatments was an
important factor in CO₂ emission rate in onions, tomatoes and cucumbers. The
differing response of various commodities to varying pressure treatments was
probably due to differences in routes of gas exchange as well as intercellular
space volumes and internal structure.
To determine if variable pressure treatments had a metabolic effect on
tissues, a dynamic head-space sampling technique was developed to collect and
concentrate aroma volatiles for analysis by gas chromatography/mass
spectrometry. Principal component analysis of pepper, onion and tomato
volatiles revealed that variable pressure storage increased levels of compounds
associated with oxidation compared to those stored under constant pressure.
Data from peppers stored under 3% oxygen and variable pressures for 1 week
indicated that compounds associated with off-flavours were lower than in
peppers stored in air. === Land and Food Systems, Faculty of === Graduate
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