The bitter taste in the juice of Washington navel, Shamouti and Valencia oranges, grapefruit and natsudaidai harvested in the early or middle term of the year, usually increases after expression from the fruit. The delayed bitterness of the juice has been a problem in food processing.
The effects of preservatory methods on the bitter taste were examined. The samples were Banpeiyu fruits (Citrus grandis OSBECK) harvested in January at the Fruittree Research Institute of Kumamoto Prefecture.
The fruits were cut, and the juice was expressed and filtered through a double cheesecloth. The juice was Preserved at 5°C or 30°C, under aerobic or anaerobic condition. For the anaerobic condition, the juice in a test tube with a groundglass stopper was charged with nitrogen gas to replace the air and kept for 32 hours. Limonoid and naringin contents were determined by HPLC, and the bitter taste in the juice was evaluated by ranking test.
The results showed, with 5% significance, that there was more bitterness in the juice preserved under the aerobic condition at 30°C. Limonin content increased, but nomilin and obacunone contents did not changed.
The naringin content did not show any differences between samples kept under aerobic and anacrobic condition.
It may be concluded that the preservation conditions of the expressed juice affect the formation of limonin and increase the bitter taste.
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