Nondestructive maturity determination in green tomatoes using a handheld visible and near infrared instrument
a b s t r a c t A nondestructive method based on visible and near infrared spectroscopy, was investigated for deter- mining the maturity of green tomatoes at harvest. The interactance spectrum of tomato fruit at the firm green stage were measured in less than 5 s with a handheld spectrometer (400-1000 nm) utilizing an optical design with a 0◦ angle between the incident illumination and the detection view. Results showed that the predominant change in the interactance spectra in green tomatoes useful for predicting chang- ing maturity levels occurred in the 600-750 nm portion of the 400-1000 nm region, typically associated with chlorophyll. Variety-specific Bayesian classification models and a joint variety 'global' classification model were developed to predict tomato maturity after 7 d of storage in a 20 ◦C ripening room using canonical discriminant analysis techniques applied to the interactance spectra from 600 nm to 750 nm. Variety specific models correctly identified 75-85% of immature tomatoes and 82-86% of mature green tomatoes in internal cross-validation, however external validation performance decreased when applied to predict maturities in a cultivar external to the training set. False positive rates of these models in identifying immature and mature green tomatoes varied from 3% to 40% and 0% to 31% respectively. A 'global' model, trained on two cultivars showed more stability and correctly predicted 71% of immature and 85% of mature green tomatoes, with false positive error rates of 13% and 22%, respectively, in internal cross-validation of both varieties. This handheld system showed good potential as a rapid, nondestructive technique to aid tomato production managers in the identification of immature green tomatoes at har- vest and could be a valuable tool in delivering more flavorful fruit to consumers by reducing the amount of immature fruit harvested by workers. © 2013 Published by Elsevier B.V.