Analysis of astringency distribution in 'Rojo Brillante' persimmon using hyperspectral imaging
Munera, S. | Besada, C. | Blasco, J. | Cubero, S. | Gil, R. | Aleixos, N. | Salvador, A.
The astringency removal with high CO2 concentration is the most widely used postharvest treatment prior to commercialise astringent persimmon cultivars. In this process the anaerobic respiration promoted gives rise to an accumulation of acetaldehyde which reacts with the soluble tannins (ST), responsible of astringency. The objective of this work was to evaluate if the process of tannin insolubilization occurring during deastringency treatment is uniform around the fruit flesh. To this end lots of ten homogeneous 'Rojo Brillante' fruits were exposed to CO2 treatments in closed containers (95% CO2 at 20°C and 90% RH) for: 0, 6, 12, 18 and 24 h. After each treatment, individual fruits were cut into halves and pressed against 10×10 cm filter paper soaked on a 5% FeCl3 solution, obtaining a blue print whose quantity and intensity is related with the ST content and its distribution. In addition, hyperspectral images of the intact fruits were previously acquired in order to predict the content and distribution of ST in the flesh in each case. The following parameters were also individually evaluated: external colour, ST content and sensory evaluation of astringency. A predictive model based on PLS was designed and applied to fruit submitted to deastringency treatments allowing creating maps of the distribution of the ST in the fruit. The classification model designed based on Partial Least Squares (PLS) was capable to differentiate those fruit in which the effectiveness of the treatment was complete (non-astringent fruit) from those in which remained ST that resulted on sensory detectable astringency. Under the study, the ST that remained after CO2-treatments were distributed irregularly inside the flesh, being their insolubilization faster in the stem-end area than in the stylar one.
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