It is desirable to monitor the quality of fresh fruit and vegetables since it benefits both producers, by offering a competitive advantage, and consumers, by improving consistency and hence encouraging a more healthy and varied diet. Near-infrared (NIR) spectroscopy is a candidate technology for monitoring agricultural produce quality. Here there has been a recent trend toward transmission-based geometries which interrogates deeper into the sample. NIR tomography is the natural progression of this, offering the possibility of detecting internal defects. The aim of this study was to evaluate a NIR tomograph built from relatively low-cost components. This comprised a stabilised VIS/NIR broadband source; a diode-array NIR spectrometer and a sample turntable. The angular positions of the detector and turntable could be moved independently of each other using two stepper motors under computer control. An experimental approach was adopted to generate a linear 'difference image' reconstruction matrix using 47 mm diameter potato cores, with a nominal length of 65 mm. and a 10 mm diameter black rod acting as an internal absorbing perturbation. The reconstruction matrix was generated for a single wavelength (689 nm) using multiple linear regression and evaluated for the case of two perturbing rods. The reconstructed image was of comparable quality to that typically obtained from other so-called 'soft-field' tomographic techniques. Although conducted under highly simplified conditions, the results suggest NIR tomography has potential for monitoring internal defects in agricultural produce.
source: Postharvest biology and technology