Tannins Are Implied in Flesh Browning of Persimmon
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Flesh browning is one of the most important disorders in the commercialisation of 'Rojo Brillante' persimmons. Mechanical damage on the packaging line has been found to be the main cause of this disorder. However the form of the tannins, that is in their soluble or insoluble-form, affects the incidence of flesh browning. 'Rojo Brillante' contains a high content of soluble tannins at harvest which results in the human perception of astringency. Therefore, fruits are subjected to postharvest deastringency treatment which leads to tannin insolubilisation (condensation). The objective of this research was to study changes in 'Rojo Brillante' tannins during deastringency process and browning expression. We used thiolytic cleavage reactions and chromatographic techniques to determine the proportion of flavan-3-ol at harvest, after deastringency treatment with CO2, and also after expression of flesh browning as a consequence of mechanical impacts. Our result showed that epigallocatechin and epigallocatechin-gallate are the major units of 'Rojo Brillante' tannins while epicatechin and epicatechin-gallate are present in lower proportions. The application of CO2-treatment clearly increased the proportion of tannins in the insoluble form. The analysis of tannins from browned flesh areas showed a chromatographic profile that suggests the formation of oligomers probably associated with the process of oxidation.