Diffusivity of CO2 and Water Vapors in `Gala' and `Granny Smith' Apples

in HortScience

Previous observations have shown that the diffusivity of water vapors is much larger than the value that is predicted theoretically from the magnitude of the diffusion coefficient of CO2, C2H4, or both. This has been ascribed to the ability of water to diffuse through the cuticle and to the transport of water via the capillaries of cellulase micorfibrels to the surface of the lenticels, where it evaporates. We measured the diffusivity of CO2 in `Gala' and `Granny Smith' apples. The former are more permeable to CO2 than the latter cultivar, in particular after prolonged storage at 2°C. The diffusivity of H2O was 10- to 20-fold larger than that of CO2. Furthermore, the ratio of D(H2O)/D(CO2) was similar for both cultivars. Infiltration of dyes and gas flow through apples submerged in water show that in `Gala' apples, the number of open lenticels is larger than in `Granny Smith'. Thus, the data indicate that lenticels are the main avenue of gas exchange in apples.

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