CHANGE OF SUGAR CONTENT IN CHESTNUT DURING LOW TEMPERATURE STORAGE

We measured the changes of sugar content and activities of enzymes related to starch degradation in five Japanese chestnut cultivars during low temperature (1°C) storage. The sugar contained in chestnut was mainly sucrose and others were hardly detected regardless of cultivar. The initial sucrose contents in early season cultivars, 'Tanzawa' and 'Kunimi', were lower than in mid season, 'Ginyose', and late, 'Ganne'. 'Riheiguri' which assumed to be an F₁ hybrid of Japanese and Chinese chestnuts, showed the highest content at the bigining. The sucrose content in each cultivar was increased with decreasing starch content during the storage. The most notable change of sucrose content was observed in early cultivars, which showed 8 to 10 times more after ten weeks. While the increasing ratio was 3 to 4 in medium and late cultivars. In Riheiguri, its content increased only about 2 fold. The sucrose content in each cultivar was almost the same (about 10%) after one month of storage. Both phosphorylase, neutral and acidic invertase activities did not increase or decrease during storage. Amylase activity tends to rise gradually during the storage, but there was no significant relationship with starch and sucrose contents. And it was revealed that chestnut amylase is a -amylase. However, the role of -amylase in the degradation of starch has not been clarified. These results indicate the possibility that starch degradation is controlled by other factors, such as debranching enzyme or inhibitors of these enzymes.