Abstract
The purpose of this study is to elucidate the mechanism of increase in bitterness of natsudaidai (Citrus natsudaidai Hayata) fruit caused by freezing and also to devise a method of determining the naringin content as related to the organoleptic taste.
1. Most of the naringin contained in the pulp segment was soluble in water. Only a little insoluble naringin was detected in natsudaidai fruit.
2. The increase in bitterness of frozen pulp segments depended on (1) an increase in naringin content of the juice exuded in the juice sacs from the sac membrane that was injured by freezing and (2) the exudation of large quantities of naringin from this membrane, especially from the stalk tissue, caused by chewing.
3. Naringin content of the pulp juice squeezed with a hand juice wringer was closely related with bitterness of the pulp.
4. Not so strict conditions were required for the measurement of naringin content by the modified Davis method that a linear regression curve, i.e., Y=0.12+4.27 X, could be used in most naringin determinations.
5. From the results obtained, it seems feasible to determine the bitterness of pulp segments even at the site of citrus growing areas. Sample juices squeezed with hand juice wringers may turn yellow when treated with Davis reagents, and then naringin content can be determined by spectrophotometry or with a color chart.
