Abstract

The acceptability of near infrared (NIR) transmission spectroscopy for the prediction of six quality factors of apples (firmness, refractive index, pH, titratable acid, dry matter and alcohol insoluble solids content) was investigated. The effects of storage conditions, cultivars and season on the accuracy of the NIR transmission method were also studied during the experiment. The accuracy of the calibration of all investigated parameters decreased during storage. The alteration of the characteristics of the spectra is possibly due to changes in the chemical composition and structure of apples between September and April. The calibration method was improved by developing a separate calibration for each cultivar per year. The calibrations of the different parameters are season-dependent except for the dry matter content. Using outlier diagnostics, the prediction accuracy can be generally improved by about 10%. The coefficient of variation for each parameter is compatible with the relative standard deviation for the reference methods except for the titratable acid content, showing the applicability of NIR transmission techniques. A relationship seems to exist between the maturity and the NIR transmission spectra of the apple.

© 1994 NIR Publications

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