Changes in the Organic-Acid Content of Valencia Oranges During Development

Abstract

The maximum amount of free acid in Valencia orange fruits was found to develop early in the season and to change very little from that time on. The concentration of free acids in the juice (milligrams per milliliter), however, lessens considerably during fruit development. This decrease in free acidity, with the corresponding increase in pH, was due chiefly to the decrease in concentration of free citric acid. Although the malic-acid concentration in the juice (milligrams per milliliter) stayed nearly uniform during the season, the actual amount in the fruit increased. The concentration of combined acids remained nearly uniform in the fruit, but the absolute amount per fruit increased. The amounts of combined acids determined from the alkalinity of the ash were in agreement with the values determined from the difference between the totaland free-acid radicals. During ripening, the changes in pH of the juice were definitely related to changes in percentages of the total-acid radical in the free form. A similar relation was noted between pH and the percentage of free acid expressed on a fresh-weight basis.