Abstract
The persimmon cv. ¿Rojo Brillante¿ is astringent at harvest due to the high
soluble tannin content and therefore it must be submitted to postharvest deastringency
treatment before commercialising the fruit. An established common
practice to remove astringency in this cultivar is to expose the fruit under
anaerobic conditions, at 95-98% CO2 for 24-36 h. This treatment allows
commercialization of non-astringent fruit with a crispy texture. The level of
astringency must be measured to ensure the treatment effectiveness. The current
methods used for this purpose are based on the soluble tannin content determination;
however, these methods are slow, subjective, and destructive. In this work,
the use of hyperspectral imaging has been studied as a potential objective method
to determine different level of astringency in persimmon. Samples of persimmon
fruit were exposed to different treatments with CO2 in order to obtain fruit
with different level of astringency. Hyperspectral images of intact fruits and
flesh slices were acquired in the range of 420-1080 nm in reflectance and transmittance
modes respectively, and the data were processed using a Partial Least
Square (PLS) analysis. For all the hyperspectral images, the average spectrums
obtained from two regions of interest were used as independent variables in
the model. The dependent variables were the tannin content estimated using
a destructive method based on the reaction of the tannins in contact with a
ferric chloride solution, and the data of astringency sensory evaluation. The
best predictive capability obtained for the model was 74.4% for the sensory evaluation in the intact fruits, and 88.5% for the content of tannins in the flesh
slices. The obtained results point to hyperspectral images is a very promising
technique for the evaluation of astringency in persimmons.
