Quality management through respiration control: Is there a relationship between lowest acceptable respiration, chlorophyll fluorescence and cytoplasmic acidosis?

Postharvest quality deterioration is generally proportional to product respiration rate. A goal of postharvest researchers has been the development of an acceptable, non-destructive method to determine the lowest acceptable respiration that is needed to maintain cell life and optimize postharvest quality. Previous research has focussed on measuring gases associated with the onset of anaerobic respiration, e.g. increases in ethanol, acetaldehyde and CO2. In this study, these methods are compared with a recently-developed method that detects an increase in the chlorophyll fluorescence parameter, F alpha, that occurs between ca. 0.2 and 2.0 kPa O-2, depending on the commodity. Apple, broccoli, asparagus and lettuce were subjected to a progressive reduction in O-2 and a return to normoxia. The anaerobic gases did not consistently appear whereas there was a consistent F alpha spike at the anaerobic threshold. The anaerobic induction of cytoplasmic acidosis in plant cells will be discussed and used to explain the fermentation gas results. Anaerobicallyinduced acidosis in the chloroplast lumen is also possible and could also explain the occurrence of the F alpha spike.