Application of Time-of-flight Near-infrared Spectroscopy for Detecting Water Core in Apples

Abstract

Time-of-flight near-infrared spectroscopy (TOF-NIRS) was used to investigate optical characteristics of water-cored tissue in `Fuji' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh. Mansf.)]. The combined effects on the time resolved profiles of water core, laser beam wavelength, and detection position of transmitted light were investigated in detail. Attenuance of peak maxima (At), time delay of peak maxima (Δt), and variation of full width at half maximum (Δw) decreased gradually as water core increased. Water-cored tissue transmitted much more energy because of the filling of intercellular spaces with liquid, so that the light path time through a sample decreased. These parameters were also strongly dependent on detection position and wavelength of the laser beam. The substantial optical path length calculated from Δt at λ = 800 nm was 10 to 17 times, while that for λ = 900 nm varied from six to 11 times the distance of the diameter of the fruit. Results indicated the optimum optical parameter for detection of water core was Δt.