Processing tomatoes into purees or sauces was already known to enhance their anti-cancer properties.
Now researchers have discovered that a combination of intense heat and fat can increase it even more.
Their findings also suggest that left-over spaghetti bolognese can be given a healthy boost by reheating.
The processing technique alters the structure of the tomato molecule lycopene so that it is more easily transported into the bloodstream and body tissues.
Previous research has shown that lycopene, a powerful antioxidant which gives tomatoes their red colour, can help prevent cancers and may also combat heart disease and diabetes. It has an especially potent effect on prostate cancer.
In the average tomato, lycopene generally has a straight or “linear” shape that hinders its ability to pass through intestinal walls into the blood.
However most of the lycopene found circulating in the bloodstream has a “bent” molecular form. Scientists believe lycopene with this kind of structure is more likely to pass into the blood and be carried around the body, where it can exert its health-giving effects.
Scientists in the US have now found a way to maximise the number of bent lycopene molecules in tomato sauce.
A trial showed that people had more lycopene in their blood after eating the specially processed sauce than they did after consuming ordinary tomato sauce.
Study leader Dr Steven Schwartz, from Ohio State University in Columbus, said: “What we have found is we can take the red tomato molecular form of lycopene and by processing it and heating it in combination with added oil, we can change the shape of the molecule so it is configured in this bent form.”
Heat is vital to the process, but so is the addition of some fat, he said.
During digestion, the body makes use of fat to produce tiny droplets called lipid micelles which are readily absorbed through the gut walls.
Bent lycopene molecules are more easily carried into the blood by the fat droplets, said Dr Schwartz.
The scientists processed red tomatoes into two kinds of sauce. One was rich in cis-lycopene - the “bent” variety - while the other mostly contained all-trans-lycopene, the linear form.
Corn oil was added to both sauces, but the key to producing “bent” lycopene was a 40 minute second round of heating at 127C.
The resulting sauce contained nine times more “bent” lycopene than sauce processed the traditional way.
A small study was then conducted on 12 volunteers who were given both types of sauce to eat.
After each meal, seven blood samples were taken and analysed over a period of nine and a half hours.
Lycopene blood levels were 55% higher after consumption of the new sauce, the scientists found.
Further clinical trials are now being carried out by the team.
Dr Schwartz presented the results today at the annual meeting of the American Chemical Society in Philadelphia.
He said the research suggested it should be possible to produce healthy “bent” lycopene in the kitchen - by re-heating left overs containing tomato sauce.
“Some people like to cook tomato sauce for prolonged periods, sometimes reheating it day after day, because it tastes better on the second and third day,” he added. “They add fat by using oil or meat, and that’s going to start to induce cis-isomers of lycopene if fat is present and the cooking continues.
“So it’s possible people could induce this process and increase lycopene absorption by routine food preparation procedures, as well.”