カキ果実の脱渋に関する研究 (第1報)

Abstract

Changes of the activities of alcoholdehydrogenase (ADH) and peroxidase as well as some chemical constituents in the process of the artificial removal of astringency in kaki fruits were studied employing Hiratanenashi, one of the most principal variety of astringent cultivar in Japan.Differences of these enzyme activities in the parts of fruits and in the course of harvesting were also investigated.The results are summarized as follows.1. The activities of ADH and peroxidase in the peel and core tissues of kaki fruits were very high, whereas those of the flesh tissues were of extremely low level.2. ADH activities of the fruits increased gradually with the delay of harvesting time, and this tendency was remarkable especially in the core tissues.3. The amount of acetaldehyde and ethanol increased remarkably with the removal of astringency. When the removal of astringency was carried out by the carbon dioxide treatment the fruits contained higher amounts of acetaldehyde and lower amounts of ethanol than did the fruits treated by the ethanol.4. ADH activities in the peel and core tissues increased gradually during the removal of astringency by ethanol treatment. In the case of carbon dioxide treatment the activities showed marked increase. However, ADH activities in the flesh tissues were held at almost same level throughout the removal treatment with carbon dioxide or ethanol.5. Peroxidase activities in the core tissues also increased markedly during the removal of astringency. In the flesh tissues however the activities showed a little increase.Three protein fractions which have activity to remove the astringency were prepared from the flesh, peel and core tissues of kaki fruits by gel-filtration with Sephadex G-200. The major activity was found in the fraction II which increased in the process of artifical removal, and the sum of activity of the fraction II amounted to 82-96% of the total activity.6. The protein contents in each part of fruits increased as astringency disappeared. There were significant differences in the gel-filtration pattern between before and after treatment for the removal of astringency.It was suggested that protein metabolism in kaki fruits might have a close relation with the mechanism of the removal of astringency, and also the function, such as high enzyme activities in the core tissues of fruits may plays an important role for the removal of astringency.