Monitoring optical properties of apple tissue during cool storage

Apples (Malus×domestica) of ‘Elstar’ and ‘Pinova’ of three different ripeness stages (unripe, ripe and overripe) were stored in separate chambers with 2°C and controlled atmosphere (2% CO2, 1.5% O2) between August 2008 and March 2009. During storage, 30 pieces of each cultivar were randomly selected for one measurement. Monochrome camera (JAI A50IR CCIR, JAI, Denmark) was used to capture images of 720x576 pixel size with 0.1694 mm/pixel resolution. The selected point on the apple surface was illuminated with circular laser beam of 7° incident angle and 785 nm wavelength (LPM785-45C, Newport Corp., USA). The vision system was controlled using LabView 8.6 PDS (National Instruments, USA) software extended with a dynamic library including image processing functions. The observed spatial distribution of intensity was used to estimate optical properties of fruit tissue. Backscattering profiles were computed based on radial averaging relative to the incident point. The logistic shape of the collected profiles was analyzed further to estimate optical properties such as absorption coefficient (μa), scattering (μs) and anisotropy factor (g). The size of the total backscattering area was also taken into account to describe light penetration and distribution in apple tissue. The method appears reasonable for characterising changes in the optical properties of fruit in postharvest.