Food for thought: Why are tomatoes red?

As now is the time time of year when tomatoes are turning from green to red in their grow-bags, it raises the question, why? Well, the reason for this attractive metamorphosis is the synthesis of small amounts of different colour pigments as the fruit ripens. An unripe tomato is coloured green by chlorophyll, the most common pigment found in unripe fruit and many vegetables. As the tomato ripens, its colour starts to change from green to yellow and then eventually to red. This is due to the breakdown of chlorophyll, which in turn synthesises a red carotenoid (another pigment group), lycopene. When ripe, the carotenoid can easily be seen as the dominant colour of the tomato, ie red. Lycopene is also the dominant colour in watermelons. And due to the resilient nature of the pigment, the colour does not fade or become dull when cooked, bottled, canned or pureed.

Roy Hallam, British Nutrition Foundation