Quality assessment of tomato fruit by optical absorption and scattering properties

This paper reports on the measurement of optical properties of tomato fruit over the wavelength range of 550-300 nm by means of a spatially-resolved diffuse reflectance technique, for assessing the firmness, soluble solids content (SSC) and pH. Spatially resolved diffuse reflectance spectra of 600 'Sun Bright' tomato samples harvested at six maturity stages were acquired using a newly developed spatially resolved spectroscopy (SRS) system, from which the reduced scattering (μ′s) and absorption (μa) coefficients were estimated using an inverse algorithm for the diffusion theory model. Tomato firmness was measured using two reference methods, i.e., compression and puncture, while SSC and pH were measured using the standard refractometry and pH meter. Partial least squares (PLS) models were developed, based on μ′s, μa and their combinations, for predicting the three quality parameters. While both μ′s and μa were correlated with tomato firmness, SSC and pH, better prediction results were obtained for the multiplication of μ′s and μa (i.e., μa×μ′s) except for puncture maximum force. PLS models gave good predictions of compression maximum force and puncture maximum force, slope and flesh firmness, with the correlation coefficients of 0.894, 0.915, 0.923, 0.835, respectively, while they had poor predictions of tomato SSC and pH with the correlation coefficients of 0.623 and 0.769, respectively. This research demonstrated that the SRS technique, along with the absorption and scattering coefficients, has potential for nondestructive measurement of quality attributes, especially firmness, of tomato fruit.