温州ミカン果肉中の有機酸に及ぼす土壌の種類の影響

Abstract

Effects of soils on the process and mechanism of organic acid formation in satsuma mandarin fruit were investigated.1. Citric acid concentration of the pulp was higher in fruit from the Tertiary rock soil than in fruit from the granite soil through the maturation period except late August. On the other hand, malic acid concentration of the pulp of Tertiary soil fruit was higher than that of granite soil fruit at an early stage of fruit growth. The concentrations of the fruits from both types of soils, however, became similar thereafter.As to the concentrations of the other minor organic acids, no effects of soils were found at any stage of the fruit maturation.2. The total amount of citric acid per fruit of the pulp of Tertiary soil fruits were higher than that of granite soil fruits. The stages at which the citric acid content was maximum were earlier in the granite soil fruits than in the Tertiary soil fruit. This finding shows that the granite soil brings about earlier fruit maturation. Malic acid content did not show any differences between the fruits from both types of soils at early stages of fruit development. No differences due to soil types were found for minor acid content.3. From the above results, it was concluded that the changes in the concentration and content of total organic acids in the pulp were due mainly to the change of citric acid. Thus, the effects of dilution due to fruit enlargement and also of the total amount of citric acid per fruit of the pulp on the concentration of citric acid were examined. As a result, the following two conclusions were obtained. (1) In July, when acid synthesis is most active, the daily increase in citric acid concentration due to the increase in synthesis of this acid is 30% higher in fruits from the Tertiary rock soil than in fruits from the granite soil. (2) In September, when the conversion of organic acid metabolism occurs, the total amount of citric acid per fruit of the pulp still increases in the Tertiary soil fruits, so that the daily decrease in citric acid concentration is smaller in Tertiary soil fruits than in the fruits from the granite soil. These two features may be the causes of the fact that the concentration of citric acid or the total amount of organic acids per fruit of the pulp remains high in the Tertiary soil fruit compared to that of granite soil fruit.