Light penetration properties of NIR radiation in fruit with respect to non-destructive quality assessment

Some issues related to the non-destructive measurement of apple quality att ributes by means of NIR reflectance spectroscopy are addressed. A compariso n was made between two optical configurations, which can be used to perform NIR-spectroscopic measurements: the bifurcated and the 0 degrees/45 degree s optical configuration. A relationship was established between the reflect ance spectra (880-1650 nm) and the soluble solids content by means of the p artial least squares technique. Depending on the data pre-processing method , correlation coefficients between 79 and 91% were obtained. The results ob tained with the bifurcated fibre were only marginally better than those obt ained with the 0 degrees/45 degrees configuration. The apple skin reflectan ce and skin transmission properties with regard to NIR radiation were also investigated. The intensity of the light source was high enough to penetrat e through the apple skin and gather information about the apple parenchyma tissue. A method was developed to calculate the light penetration depth for each wavelength in the range from 500 to 1900 nm. This method was applied to measure the light penetration depth in 'Jonagold' apple fruit tissue. Th e penetration depth is wavelength dependent: up to 4 mm in the 700-900 nm r ange and between 2 and 3 mm in the 900-1900 nm range. (C) 2000 Elsevier Sci ence B.V. All rights reserved.