In the US, tomato ketchup comes in purple and green varieties as well as the traditional red. Betty Ishida and Mary Chapman at the Agricultural Research Service in Albany, California, wondered if the colouring might be indicative of low levels of lycopene, the pigment that makes tomatoes red. The chemical has been shown to help protect against breast, pancreatic, prostate and intestinal cancer, especially when eaten with fatty foods. There is also evidence that lycopene can reduce the risk of heart attacks.
The researchers tested lycopene levels and antioxidant activity in 13 ketchup brands: six popular ones, three organic, two store brands and two from fast-food chains. Purple and green ketchups had a similar lycopene content to their plain red counterparts. But organic ketchups excelled, with one brand containing 183 micrograms of lycopene per gram of ketchup, about five times as much per weight as a tomato. Non-organic brands averaged 100 micrograms per gram, with one fast-food sample containing just 60 micrograms per gram (Journal of Agricultural and Food Chemistry, DOI: 10.1021/jf0401540). If you want high lycopene levels, says Ishida, the rule of thumb is to pick the darkest red ketchup.
Source: www.newscientist.com, news of 2005-01-08.