A permeation-diffusion-reaction model was applied to study gas exchange of apple fruit (Kanzi, Jonagold, and Braeburn) as effected by morphology and respiratory metabolism. The gas exchange properties and respiration parameters of the fruit organ tissues were measured. The actual internal tissue geometry of the fruit was reconstructed from digital fruit images and the model was solved over this geometry using the finite element method. The model was validated based on measurements of internal gas concentrations and the gas flux of the fruit to its environment. Both measurements and an in silico study revealed that gradients of metabolic gases exist in apple fruit, depending on diffusion properties and respiration of the different cultivars. Macroscale simulation confirmed that Jonagold has large potential for controlled atmosphere (CA) storage while low diffusion properties of cortex tissue in Braeburn indicated a risk of storage disorder development. Kanzi had less O(2) anoxia at CA storage compared with Braeburn.

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A permeation diffusion reaction model was applied to study the internal metabolic gas concentration inside apple fruit cv 'Kanzi', 'Jonagold' and 'Braeburn' under controlled atmosphere (CA) conditions. A new criterion for the local O 2 partial pressure beyond which there is a risk of cell death due to energy shortage was established as the local O 2 partial pressure at which the oxidative ATP production becomes smaller than the maximal ATP production by fermentation. The Michaelis-Menten constant (2 , mO K) of oxidative respiration of apple tissue at 1°C was within 0.13-0.17 kPa. At an O 2 partial pressure of 0.46 to 0.78 times the 2 , mO K at a storage temperature of 1°C, energy production for cell maintenance could be still secured in the three cultivars. The effect of natural variability of the maximal respiration rate and tissue gas diffusivities inside apple fruit was further studied by means of a Monte Carlo analysis. The simulations confirm that 'Jonagold' has large potential for storage under low O 2 partial pressure, while 'Kanzi' and 'Braeburn' need to be stored at higher O 2 partial pressure, in line with commercial practices.

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