Changes in tannins, ascorbic acid and sugar content in astringent persimmons during on-tree growth and ripening and in response to different postharvest treatments

Changes in tannins, ascorbic acid and sugars in astringent persimmons ‘Rojo Brillante’ and ‘Kaki Tipo’ were investigated during fruit maturation and after postharvest treatments. Soluble tannins exhibited a significant initial increment, followed by a marked constant decrease that led to values between 0.2 and 0.3 g/100 g fresh weight (FW) in the last stage of maturity studied. During the entire period monitored, insoluble tannins represented the minor component of the total tannic fraction, accounting for 9–27% (Rojo Brillante) and 17–32% (Kaki Tipo) of total tannins; levels of insoluble tannins were comparable to or higher than the soluble tannins in softer fruits. Total vitamin C decreased from 0.18–0.20 to about 0.08 g/100 g FW during fruit development owing to fruit growth rather than to degradation processes. Total sugars increased from about 4 g/100 g FW at the early stage of fruit development to 17 g/100 g FW after reaching the commercial stage of maturity. Glucose and fructose increased during the entire period monitored, while sucrose reached a maximum and then gradually decreased, probably owing to a strong invertase activity. Antiradical activities were significantly related to the corresponding tannic fraction. In both ‘Rojo Brillante’ and ‘Kaki Tipo’, postharvest treatment with CO2 was more effective than with ethylene in reducing soluble tannin concentration (0.031–0.067 and 0.220–0.262 g/100 g FW, respectively).