Simultaneous measurement of oxygen and carbon dioxide diffusivities in pear fruit tissue using optical sensors

Gas diffusion properties of pear tissue are important in relation to gas exchange of the fruit with its environment during storage. In this contribution, a set-up for measuring tissue diffusivity using fluorescent optical probes was developed. O-2 and CO2 diffusivities were determined simultaneously based on a finite element model describing simultaneous O-2 and CO2 gas transport as well as respiration in the tissue. The effect of variations on the diffusion set-up conditions such as the volume of the measurement chamber and thickness of the sample on the accuracy of the estimated diffusivities was investigated using a sensitivity analysis on simulated data. The optical sensors produced good informative O-2 and CO2 partial pressure versus time profiles. The average O-2 and CO2 diffusivity of pear cortex tissue was (2.56 +/- 0.48) X 10(-10) m(2) s(-1) and (3.8 +/- 1.1) x 10(-9) m(2) s(-1), respectively. The coefficient of variation of diffusivity of O-2 and CO2 in pear tissue due to bias, variation of the sample thickness and volume of the measurement chamber was 2.0-2.3% and 2.1-2.4% for a measurement chamber volume between 7.5 and 15 mL and a tissue thickness of 1-2.5 mm, respectively. The variability of estimated diffusivities due to measurement errors was eight times smaller than the biological variability. (c) 2007 Society of Chemical Industry.