THE ORGANIC ACIDS OF GRAPEFRUIT JUICE

Abstract

The organic acids of grapefruit juice are citric and malic acids. The total acid content precipitated from grapefruit juice by lead acetate is equal to the sum of the citric and malic acids. The titration curve of grapefruit juice is very similar to that of a pure citric acid soln., provided a correction is made for the combined acid naturally occurring in the juice. There is a definite relation between the pH and the amt. of acid in the salt or combined form. The small fluctuations in pH of mature grapefruit juice are correlated with the large ratio of free acid/combined acid. The free acids decreased and the pH of the juice increased with increase in fruit size. The decrease of the free-acid conc. in grapefruit during development is due chiefly to the increase in fruit size rather than to a change in the absolute amt. of free acid per fruit. The alkalinity of the ash is a measure of the base-forming capacity of the juice, as well as a measure of the cations combined with the organic acids. In grapefruit juice, > 50% of the total cations are utilized in the formation of the organic acid salts, as compared to > 70% in the juice of Valencia and navel oranges. A large increase in available cations from soil fertilization would produce a limited increase in combined acid and little decrease in juice acidity.