Ethanol and Frozen-Thawing Treatments for ’Damopan’ Persimmon Astringency Removal
|School||Huazhong Agricultural University|
|Keywords||Oriental persimmon (Diospyros kaki Thunb.) Tannin Astringency removal Ethanol treatment Frozen-thawing treatment|
Oriental persimmon (Diospyros kaki Thunb.) originated from China, but most of cultivars are pollination constant astringent type which distributed in front of house and the edge of field. There is still relatively high content of soluble tannins in astringent persimmon fruits when ripened, not being edible, they have to be artificially removed astringency after harvest before they are edible. On the other hand, the major methods of astringency removal in commercial treatment are CO2 gas treatment and ethanol vapor treatment, which it’s difficult for ordinary farmer to grasp and use. However, eating some persimmon fruits, which are not completely removed astringency, may be the main cause to lead to persimmon bezoar.In this study,’Damopan’ (PCA) which is the most widely distributed and the largest cultivated in China, were used as materials. Some physiological parameters were determined to evaluated the effects on astringency removal by ethanol treatment and frozen-thawing treatment in order to establish the convenient effective techniques for common consumers.The main results are as follows:1. After ethanol treatment (fruits were put into a 0.05 mm thick polyethylene bag after 35% ethanol treatment and then kept at 20℃for 4 days), the fruit firmness of ’Damopan’continuously decreased during ethanol treatment, from 12.49kg/cm2 to 7.67kg/cm2 (after 4 days), but is still considered to fit for sale. The fruit firmness values were 3.95kg/cm2 after 6 days ethanol treatment. After frozen-thawing treatment (-18℃frozen for 40 days), the fruit firmness of ’Damopan’ is too hard to be determined, but the softening was significantly greater when thawing.2. The soluble solids content showed similar trends between ’Damopan’ fruits after ethanol treatment and frozen-thawing treatment. However, the former increased slowly in the early stage and then stay at 15.07% and the latter decreased at the beginning and stay at 17.33%.3. The soluble tannin content of ’Damopan’ fruits were significantly less after ethanol treatment than control and disappeared completely after 4 days (only 0.04%). The insoluble tannin content showed the opposite trend to the soluble tannin and reached the maximum (1.15%) after 4 days. After frozen treatment, the soluble tannin content reduced to 0.86%, but it decreased significantly during thawing treatment and completely removed astringency after thawed 48 hours (only 0.02%). The insoluble tannin content increased greatly and reach the maximum (1.10%) during thawing.4. The tannin cell size has no remarkable difference between control and ethanol treatment, but the surface of tannin cell significantly shrank and color was deepened. After frozen-thawing treatment, the tannin cells were completely damaged, so their size can not be determined.These results showed that for’Damopan’, astringency could be easily removed by ethanol treatment (fruits were put into a 0.05 mm thick polyethylene bag after 35% ethanol treatment and then kept at 20℃for 4 days) and by Frozen-thawing treatment (fruits were put into a conventional freezer at -18℃for 40 days and then thawed at room temperature (20℃)).