Changes in the non‐volatile organic acids of tomato fruit during ripening

A study has been made of the individual non‐volatile organic acids in ethanolic extracts of tomato fruit during ripening. Whole fruit of three varieties and the outer walls and locular contents of one variety each at five stages of ripeness from mature green to full red were analysed. No trace of many of the K rebs‐cycle acids could be detected. Maximum citric acid concentrations were found at either the green‐yellow or yellow‐orange stage of ripeness according to variety. Malic acid concentrations and the malic/citric acid ratio decreased progressively as the fruit ripened. Glutamic acid increased approximately ten‐fold and aspartic acid more than doubled from the mature green to red stage of ripeness, but changes in pyrrolidonecarboxylic acid (PCA) during ripening were not statistically significant. In general, similar trends were observed in whole fruit and in the outer walls and locular contents, but malic, citric, glutamic and aspartic acid concentrations were higher in the locular contents than in the outer walls at all stages of ripeness. Alcohol‐insoluble solids (AIS) decreased markedly between the green and green‐yellow stages and then more slowly with further ripening.