Nondestructive detection of brown heart in pears by time-resolved reflectance spectroscopy

Abstract

Brown Heart (BH) is an internal disorder sometimes seen in pears under controlled atmosphere (CA) storage. The symptoms are not externally recognizable and are visible only after cutting the fruit. Time-resolved reflectance spectroscopy (TRS) is a novel nondestructive means for the complete optical characterization of highly diffusive media that allows the simultaneous evaluation of their absorption coefficient μa and transport scattering coefficient μs′. The aim of this work was to test whether TRS can be used to detect BH in intact fruit. ‘Conference’ pear fruit with low risk (early harvest, low CO2 CA storage) and high risk (late harvest, high CO2 CA storage) for BH were measured with TRS at 690 and 720 nm on 8 points around the equator. BH was detected in pears by an increase in the absorption coefficient μa at 720 nm, which was significantly higher than that in sound tissue. Sound tissue had μa at 720 nm ≤0.04 cm−1. The absorption coefficient μa at 690 nm responded by both increasing in the presence of BH in affected fruit and decreasing with ripening in sound fruit, so it alone can not have a unique interpretation. The decrease of the absorption coefficient μa at 690 nm in sound fruit can be attributed to degradation of chlorophyll, which has an absorption peak at 675 nm. Scattering coefficient μs′ at 720 nm was influenced by translucency of water-soaked tissue, as in over-ripe fruits and in bruised regions. This technique allows a description of the virtual appearance of the internal tissue in the intact fruit to a depth of 2 cm, including presence of defects and their position inside the fruit.