A NEARâINFRARED SENSING TECHNIQUE FOR MEASURING INTERNAL QUALITY OF APPLE FRUIT

Abstract

Nearinfrared (NIR) spectroscopy is a promising technique for nondestructive sensing of apple fruit for multiplequality attributes. The objective of this research was to investigate a NIR sensing technique in interactance mode for rapidacquisition of spectral information to predict the sugar content and possibly firmness of apple fruit. A NIR sensing systemwith a specially designed probe assembly was used for simultaneous acquisition of spectral data at two different distances(3.5 and 5.5 mm) from the light source in the spectral region between 900 and 1500 nm. Experiments were performed to collectspectral data from two apple cultivars: Empire and Red Delicious. Chemometric models were developed using partial leastsquares regression. Better predictions of the sugar content of apples were obtained at a closer sensing position, 3.5 versus5.5 mm, from the light source. The correlations of prediction for sugar content were equal to, or greater than, 0.81 andprediction errors were between 0.5 and 0.7% for the two cultivars. Firmness predictions for Empire were not as good as thosepredictions for sugar content with a prediction error of 10.6 N at 3.5 mm and 9.8 N at 5.5 mm. Ratio spectra from the twosensing positions did not give as good predictions of the fruit sugar content and firmness as those predictions by relativereflectance. This research shows that the proposed NIR sensing technique can be used for rapid determination of fruit sugarcontent. However, it is still difficult to accurately predict fruit firmness with NIR spectroscopy.