Nondestructive Measurement of Tomato Postharvest Quality Using a Multichannel Hyperspectral Imaging Probe

Abstract. A multichannel hyperspectral imaging probe with 30 optic fibers covering the wavelength range of 550-1,650 nm and the light source-detector distances of 1.5-36 mm was recently developed for optical property measurement and quality evaluation of food products with flat or curved surface. This paper reports on an initial study of using this multichannel probe for assessing postharvest quality of tomato fruit. Spatially-resolved spectra were acquired for 600 ‘Sun Bright‘ tomato fruit of six maturity stages. Firmness, soluble solids content (SSC) and pH of the tomato fruit were measured using standard destructive techniques. Partial least squares models for single spectra and two- and three-spectra combinations were developed and compared to determine the optimal models for prediction of firmness, SSC and pH. Results showed that the 15 single spectra (or channels) gave a relatively large range of predictions, as measured by the correlation coefficient of prediction or r_p, for firmness (r_p=0.898-0.932), SSC (r_p=0.630-0.761) and pH (r_p=0.707-0.817), and the optimum single spectra were different for predicting each quality parameter, which indicates the importance of selecting an appropriate channel for predicting the quality parameters. While the optimum combinations of two or three spectra gave somewhat better predictions for firmness and SSC, compared with the optimum single spectrum, the improvements were small. SSC and pH predictions were influenced by the light source-detector distance and better predictions were obtained from those channels with small light source-detector distances. The results showed that spatially-resolved hyperspectral imaging probe has potential for measuring quality attributes of tomato fruit.