Nondestructive determination of the astringency of pollination-variant persimmons (Diospyros kaki) using near-infrared (NIR) spectroscopy and nuclear magnetic resonance (NMR) relaxometry

Pollination-variant persimmon (Diospyros kaki) fruit exhibits two distinct phenotypes based upon pollination status. Pollinated fruit are seeded and develop flesh that is brown in color, nonastringent, delectable in taste and highly desirable, whereas non-pollinated fruit retain unseeded orange-color flesh that is astringent and virtually unpalatable. Growers face the problem that both types of flesh may be present in the same persimmon fruit, and external skin color is uniformly orange, regardless of the extent of astringency. Thus, in this work, the nondestructive measurement modalities of nuclear magnetic resonance (NMR) relaxometry and near-infrared (NIR) spectroscopy were investigated for their ability to screen pollination-variant persimmons for extent of nonastringent flesh. Fruit from a diverse sample set – including six cultivars stored for varying lengths of time and exhibiting an array of astringency levels – was subjected to the two nondestructive measurements and then evaluated destructively for astringency using a sequential blotting and visual sensory analysis approach. The sensory astringency score was then used as the response variable to construct partial least squares – discriminant analysis (PLS-DA) models from spectra from each modality on its own as well as for concatenated spectra, which combined the information from both modalities. These PLS-DA models performed well, showing a maximum misclassification rate of 33%. When the most market-relevant astringency threshold was used, NIR slightly outperformed NMR. When different astringency screening thresholds were considered, combining the two modalities did not consistently improve PLS-DA model performance. Thus, both modalities show promise for nondestructive characterization of the flesh of pollination-variant persimmons.