Sarah Shaw, of Aranui High School, asks :-

What acids are in tomatoes?

John Walker, a biochemist in the Department of Plant and Microbial Sciences at the University of Canterbury, responded.

Speaking botanically tomatoes are actually fruits, although many people think that they are vegetables. In fact, when tomatoes were first introduced to Europe from South America they were called 'love apples'.

Most fruits contain a number of different organic acids of which malic acid and citric acids are the commonest and predominate in apples and lemons respectively. The pH of tomato juice is about 4.3 which is quite acid and typically contains between 0.05 - 0.2 per cent malic acid and 0.3 - 0.47 per cent citric acid depending on variety and state of ripeness. In addition traces of many other organic acids (succinic, tartaric, chlorogenic, etc) have been found in tomatoes and other fruits. Tomatoes are also a good source of Vitamin C and contain around 23mg ascorbic acid per 100g fruit (compare with 5mg/100g for apples).