Determination of sugar content in intact peaches by near infrared spectroscopy with fiber optics in interactance mode

To develop a nondestructive sugar analyzer for intact peaches, the potential of the near infrared (NIR) method with fiber optics in interactance mode was evaluated. In 'Shimizu Hakuto', a white peach cultivar, there were clear differences among the NIR second derivative spectra of high, medium, and low Brix values in the wavelength region around 906 nm. This wavelength was assigned to sucrose and selected as first calibration wavelength. The highest multiple correlation coefficient of 0.97 was obtained in the linear regression equation that included four optical terms of d2log(1/R) at 906, 878, 870 and 889 nm, while a standard error of calibration (SEC) was 0.48°Brix. A bias-corrected standard error of prediction (SEP) was 0.50°Brix with a bias of 0.01°Brix, suggesting that the MR method is sufficiently accurate to determine sugar content in intact peaches to be practical.