Metabolism of Limonoid in Banpeiyu

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The mechanism of the increase in bitterness in citrus fruits was studied. Limonin D-ring lactone hydrolase was extracted from Natsudaidai seeds and purified by ion exchange chromatography and gel filitration, resulting in a sevenfold increase in its specific activity. Examination of the metabolism of limonoid in different parts of citrus fruits revealed the presence of a dark crystalline substance around the circumambient cortex cells of the stem. Obacunone was found to be transferred from the testa to the cotyledon and stored as limonin. Limonoate A-ring lactone was formed in the leaf and the stem from September to December, then transferred to the stem cortex. It was stored in the fruits as neutral limonoid.The change in the bitterness during marmalade preprocessing was investigated. Fruits with high limonoid contents tended to lose their good flavor on boiling, whereas those with high naringin levels were judged to be significantly better tasting. Boiling the peel caused limonoate A … More -ring lactone from limonin to be transferred to the peel. At about 10 minutes after boiling was started, 17-dehydrolimonoate A-ring lactone was detected. Further heateing caused an increase in the amount of nomilin, which is thought to cause bitterness in marmalade. Fruits with large amounts of limonin tend to be favored, and mixing two types of fruits should be helpful for improving the flavor by reducing bitterness, increasing sweetness and mellowing the sourness.Fruits liquor was prepared with Banpeiyu, and the amounts of the bitter principles limonind and naringin that dissolved into the alcohol were measured. Large amounts of limonin were found in ethyl alcohol and white liquor and also of nomilin in ethyl alcohol and water. When the peel was removed and only the fruits flesh was spaked in white liquor, the resulting liquor was tahty and without bitterness, making it suitable for use as a fruit liquor.The delayed apperance of bitterness in fruit was also studied. The fruit juice was kept at 5ﾟC to 20ﾟC (room temperature) and the activation level of increase of bitterness in the juice. Less