Effect of atmospheric pressure fluctuations on bulk gas flow and composition of flavour volatiles from bulky plant tissues

• Main Author: Buckley, Katherine Elaine
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/7197

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.