The effect of modified atmospheres on the rate of quality change in 'Hass' avocado

Gas exchange rates and quality changes of avocados (Persea americana, Mill., cv. 'Hass') stored at 7 degreesC in 32 different modified atmosphere (MA) conditions generated using a flow-through system, were monitored to characterise their functional relationship. An integrated modelling approach was used to link rates of quality loss to the rate of gas exchange. This revealed a close quantitative relationship between the gas exchange of 'Hass' avocado fruit on one hand and weight loss, colour change and softening on the other, indicating a direct metabolical link between these processes. High CO2 lowered the respiratory quotient of avocado, an effect which, based on literature, could be explained by a shift from oxidative phosphorylation into the alternative respiratory pathway. In the model approach, the rates of quality degrading processes were linked to oxidative phosphorylation only, assuming this is where ATP was being produced. At high CO2 levels at aerobic conditions, unaccounted weight loss data indicated a considerable volatile production which, however, was not qualitatively characterised. Both weight loss and colour change indicated the involvement of anaerobic processes at low O-2 levels. At 2 kPa O-2 and 0 kPa CO2 no CO2 injury occurred, while the change in hue was minimal, weight loss was minimised, and softening was almost completely inhibited. At such low O-2 levels, no additional benefit was found from raising the levels of CO2. (C) 2002 Elsevier Science B.V. All rights reserved.