Simultaneous measurement of oxygen and carbon dioxide diffusivity in pear fruit tissue

Diffusion and respiration characteristics of pear tissue are needed to estimate the composition of the internal atmosphere of a pear fruit. In this contribution, a methodology is described to measure diffusion characteristics of tissue. The experimental set-up consists of two thermostatted chambers separated with a slice of fruit tissue. A gradient was established over the sample by applying different gas concentrations to both chambers. Due to this gradient, gas diffused from one chamber into the other through the tissue sample. A mathematical model consisting of six differential equations (two for each atmospheric gas) was used to describe this gas transport process through the tissue taking into account diffusion, loss of gas due to sampling, pressure-driven bulk transport, and gas consumption and production due to respiration and oxidation. The diffusion parameters of different respiratory gases in pear fruit tissue could be accurately estimated. The CO2-diffusivity in the fruit flesh (19.2 x 10(-9) m(2) s(-1)) was found to be larger than in the skin (1.15 x 10(-9) m(2) s(-1)) and larger than the O-2-diffusivity (2.10 x 10(-9) m(2) s(-1) in the fruit flesh and 1.03 x 10(-9) m(2) s(-1) in the skin). The gradient in CO2-diffusivity in the fruit was significant, with the smallest CO2-diffusivity in the skin and the highest near the core of the pear fruit. There was no change in diffusivity in the weeks prior to and after the optimal harvest date for long-term storage. (C) 2003 Elsevier B.V. All rights reserved.