Changes in acid contents of tomato fruits during development

The acid contents of tomato fruits (Fukuju No. 2) were determined at weekly intervals from flowering to one week after the turning colour stage.Three stages were recognized in the changes of free, total, and combined acidities of the fruits during development. In the first stage (from the flowering to one or two weeks after the flowering) total and combined acidities were very high, while titratable acidity remained low. In the second stage (from two or three weeks after the flowering to the turning colour stage) total and combined acidities fell suddenly to the minima at the beginning. Thereafter total acidity progressively increased to the peak value at the turning stage, while combined acidity remained low or continued to decrease, So the titratable acidity increased. During the third stage (after the turning stage) total and titratable acidities tended to decrease, while the combined acidity showed no change.The titratable acidity expressed as percentage of the total acidity rose almost linearly from 17-19% at the first week after flowering to 56-59% at the turning stage and then became constant.About 90% of the total cations was occupied by potassium, the change of which was similar to that of combined acidity during fruit development.In both the gelatinous pulp and the outer wall, the acidities followed the similar pattern to that of the whole fruits, except that the gelatinous pulp had higher acidities than the outer wall.Changes in the contents of citric and malic acids had the similar pattern to that of the total acidity, while acetic, formic, hydrochloric, and phosphoric acids continued to decrease throughout the fruit development. The sum of citric and malic acid contents occupied about 60% in the total acidity. The ratio of malic to citric acid content remained about 1:5 before the turning stage, and later became to about 1:10 due to the comparatively rapid decrease in malic acid content.