Comparison between the astringency removal of 'Hiratanenashi' and 'Denkuro' persimmon applying ethanol treatment on-tree and after harvest

In this research, the efficacy of two different ethanol treatments on astringency removal was evaluated in 'Hiratanenashi' and 'Denkuro' persimmon cultivars. Fruits from both cultivars were treated with ethanol on-tree or after harvest. A silica-ethanol patch was attached onto the peel of individual fruits on-tree or harvested fruits kept under the tree for 3 days. On-tree treated 'Hiratanenashi' and 'Denkuro' fruits were harvested at the fully colored stage, after 2 and 4 weeks respectively from treatment. Fruit treated after harvest was kept under the tree until the on-tree treated fruits were harvested. The on-tree treated fruits of both cultivars maintained flesh firmness until harvest. Soluble tannin concentration in the flesh of 'Hiratanenashi' fruit decreased, rendering the fruit non-astringent before harvest, whereas 'Denkuro' fruit showed almost no soluble tannin reduction. This may be because, unlike 'Hiratanenashi' fruits, 'Denkuro' fruits did not accumulate acetaldehyde; nevertheless, rather high amounts of ethanol were accumulated in both cultivars. In contrast, when ethanol was applied after harvest, 'Denkuro' fruits suffered a greater softening than 'Hiratanenashi' fruits. No sensorial astringency was noted in 'Hiratanenashi' fruits about 2 weeks after the treatment, whereas 'Denkuro' fruits remained astringent even 4 weeks after the treatment. The acetaldehyde and ethanol accumulations in the fruit flesh for both cultivars were almost similar to those in the flesh of on-tree fruits. The peel surface where the patch was attached showed slight staining in both cases. Our results reveal clear differences in the astringency removal between 'Hiratanenashi' and 'Denkuro' fruit treated with ethanol on-tree or after harvest.