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A commercially available Near Infrared (NIR) instrument was modified and fitted with fiber optics to measure NIR transmittance spectra in intact fruits. With this modification the potential of the NIR transmittance method to determine the Brix value in satsuma mandarin was examined. To reduce the fruit size effect which affected the NIR spectra, the 2nd derivative spectra were normalized by being divided by 2nd derivative value at 844 nm, which had a high correlation to the diameter of the fruit. Using 50 selected samples, multiple regression analysis was carried out to relate the Brix value to the normalized 2nd derivative spectra. The highest multiple correlation coefficient was 0.989 with a standard error of calibration (SEC) of 0.28 °Brix. The bias-corrected standard error of prediction (SEP) was 0.32 °Brix with a bias of -0.02°Brix. It is concluded that the NIR transmittance method yields an accurate estimate of the Brix value in intact satsuma mandrins.
Kawano et al. (Fri,) studied this question.