You say tomato

A report published just a few weeks ago revealed the results of a decade-long study evaluating organic versus conventionally grown tomatoes. The study showed that organic tomatoes increased in their concentration of three flavonoids studied over time whereas the levels of flavonoids did not vary significantly through time in conventional tomatoes. Mean values for quercetin and kaempferol in organic tomatoes were 79% and 97% higher than those in conventional tomatoes, respectively.

'Flavonoids are a class of bioactive plant compounds that help protect plants from UV-radiation, chemicals and other environmental stressors. In humans, flavonoids help protect cells against environmental insults that may contribute to chronic disease. Several population-based studies suggest that diets rich in flavonoids may help protect against cardiovascular disease, certain cancers and other age-related conditions, such as dementia. Maximizing the flavonoid content of fruits and vegetables could provide a public health benefit.'

The mechanism involved is suspected to be related to the availability of soil nitrogen. Plants with limited nitrogen accumulate more flavonoids than those that are well-supplied.

You can read a press report on the story or read the research report itself: Ten-Year Comparison of the Influence of Organic and Conventional Crop Management Practices on the Content of Flavonoids in Tomatoes

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