Tomatoes have long been known to be a good source of lycopene, the phytochemical which makes them red but which also has significant antioxidant properties. Now new research has shown that this antioxidant power can be boosted even more through the simple act of cooking the tomatoes.
Researchers from Cornell University in the US said that cooking the tomatoes increase the level of phytochemicals they contain, although it also reduces the amount of vitamin C found in the vegetable.
Writing in the latest issue of the Journal of Agriculture and Food Chemistry Rui Hai Liu, Cornell assistant professor of food science, said: "This research demonstrates that heat processing actually enhanced the nutritional value of tomatoes by increasing the lycopene content that can be absorbed by the body, as well as the total antioxidant activity. The research dispels the popular notion that processed fruits and vegetables have lower nutritional value than fresh produce."
Tomato samples were heated to 88 degrees Celsius for two minutes, 15 minutes and 30 minutes. Consistent with previous studies, vitamin C content decreased by 10, 15 and 29 per cent respectively when compared to raw, uncooked tomatoes. However, the research revealed that the beneficial trans-lycopene content of the cooked tomatoes increased by 54, 171 and 164 per cent respectively.
Levels of cis -lycopene (which the body easily absorbs) rose by 6, 17 and 35 per cent respectively. Antioxidant levels in the heated tomatoes increased by 28, 34 and 62 per cent, respectively.
While the antioxidant activity in tomatoes is enhanced during the cooking process, vitamin C loss occurs when the food's ascorbic acid is oxidised to dehydroascorbic acid and other forms of nutritionally inactive components. Lycopene is the most-efficient single oxygen quencher, and devours more than 10 times more oxygenated free radicals than vitamin E, Cornell researchers said.
"This makes lycopene's presence in the diet important," said Liu. "While these findings go against the notion that processed fruits and vegetables have lower nutritional value, this may create a new image for processed fruits and vegetables. Ultimately, this could increase consumers' intake of fruits and vegetables and could possibly reduce a person's risk of chronic disease."
A timely piece of research, given the recent decision by the British Dietetic Association to endorse canned foods from Heinz as contributing towards the healthy eating target of five fruits of vegetables a day.