The permeability concept: A useful tool in analyzing water transport through the sweet cherry fruit surface

Rain cracking of sweet cherry fruit is thought to be related to a net transport of water into the fruit. This net transport may occur along various pathways and in different directions, i.e., through the fruit surface and along the pedicel fruit juncture as uptake into the fruit or transpiration from the fruit surface. In addition, vascular transport through the pedicel may contribute to rain cracking. Water transport through the fruit surface may be described quantitatively using Fick’s law of diffusion, where the amount of water taken up into or transpired from the fruit surface is expressed as the product of the fruit surface area, the driving force for water transport and the permeability of the fruit surface. Analyzing water transport on this basis allows prediction of the effect of selected fruit factors on net water transport ; the leakiness of the stem/fruit juncture, the effect of fruit size, the magnitude of the driving force, the skin permeability or the effect of environmental variables such as relative humidity or the percentage of the fruit surface area wet. This modeling approach may be extended and a complete fruit water balance established by including estimates for vascular transport through the fruit pedicel. Examples using literature sources are provided of how these calculations may be used to identify important determinants in cracking.