Carbon dioxide treatment to reduce soluble tannins and astringency in persimmons is sometimes ineffective. Near-infrared spectroscopy was used to develop a predictive model for soluble tannin content and persimmon classification. A model using averaged spectra collected in the interactance mode showed better performance (correlation coefficient of prediction, r p = 0.95 and root mean square error of prediction, RMSEP = 0.17% w/w) than that from the transmittance mode (r p = 0.94 and RMSEP = 0.19% w/w). Models generated using spectra from the stem-end or middle plane flesh and whole fruit were comparable. Classification accuracy of 97.1% was achieved using stem-end flesh spectra. Therefore, near-infrared spectroscopy is a rapid and non-destructive technique with potential applications in the estimation of persimmon tannin content.

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Summary This research investigated the maturity assessment of pomelo using acoustic properties obtained from an impact of fruit, optical properties of the peel and variables related to oil glands from peel images. Pomelo samples were harvested at 5.5, 6.0, 6.5 and 7.0 months after anthesis. All nondestructive variables were used to build qualitative models with partial least squares discriminant analysis. The classification model based on the nondestructive variables showed that fruits could be separated into immature, early‐mature and late‐mature groups with an accuracy of 96.7%. The important variables contributing to the classification were the impact response based on the second‐order resonant frequency and the difference of green colour between the oil gland and the peel.

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