Turning up the heat on the red tomato during processing has the
potential to give the popular garden staple added disease-fighting
power, Ohio State University research suggests.
Scientists have found that lycopene molecules in tomatoes that are
combined with fat and subjected to intense heat during processing are
restructured in a way that appears to ease their transport into the
bloodstream and tissue. The tomato is the primary food source of
lycopene, a naturally occurring pigment linked to the prevention of
cancer and other chronic diseases.
In its standard structure in the average red tomato, the lycopene
molecule is laid out in a linear configuration. That structure seems to
hinder the molecule’s absorption through intestinal walls and into the
blood, said Steven Schwartz, an investigator in Ohio State’s
Comprehensive Cancer Center and a professor of food science and
technology at Ohio State.
Meanwhile, most of the lycopene that is found circulating in human
blood is configured in a bent molecular form. This means that either
the human body somehow transforms lycopene molecules through reactions
that have yet to be identified, or that the bent molecular structures
of lycopene are much more likely to be absorbed into the blood and
transported to tissue – a necessary step in preventing disease.
Assuming the latter is true, Schwartz and colleagues have devised a
way to process red tomatoes – the variety preferred by American
consumers – into a sauce that contains bent molecular forms of
lycopene. A clinical trial conducted in collaboration with Steven
Clinton, a medical oncologist and physician scientist in Ohio State’s
Comprehensive Cancer Center, showed that people had more lycopene in
their blood after eating the specially processed sauce than they did
after eating regular red tomato sauce.
Schwartz described the research today (8/20) at the American Chemical Society meeting in Philadelphia.
In the food science world, processing gets a bad rap for its
tendency to deplete vegetables of nutrients, change their color and
often negatively affect how they taste.
"Instead, here is a case where processing is positive in terms of enhancing absorption of lycopene," said Schwartz.
Lycopene belongs to a family of antioxidants called carotenoids,
which give certain fruits and vegetables their distinctive colors.
Carotenoids’ antioxidant properties are associated with protecting
cells and regulating cell growth and death, all of which play a role in
multiple disease processes.
In its natural state, lycopene in a red tomato is in what is called
an all-trans configuration, characterized by its linear form. The
molecular structure of lycopene circulating in human blood is in what
is called a cis-isomer configuration, or a bent form. The chemical
properties are the same – only the configuration differs.
"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," Schwartz said.
Heat is essential to the process, but so is adding some fat,
Schwartz said. In previous work, he and colleagues determined that
consuming fat and carotenoids simultaneously improved absorption of
lycopene and other compounds, but the scientists weren’t sure exactly
When humans eat fats, or lipids, the body produces tiny droplets of
fat called lipid micelles during digestion that are easily taken up
through the intestinal wall and absorbed into the bloodstream.
Continuing research has led Schwartz to hypothesize that lycopene in
its linear form tends to stack and become crystallized, which lowers,
but does not eliminate, its absorption potential. But the bent forms of
lycopene are able to more easily find their way into the lipid micelles
during digestion, and increasing amounts of the antioxidant in that
form are more likely to be transported to the blood along with the
Taking all this into consideration, the researchers processed red
tomatoes into two kinds of sauce: a sauce rich in cis-lycopene, the
bent configuration, and a sauce containing mostly all-trans-lycopene,
the linear form. Both sauces were flavored similarly and initially
heated using the same methods. Corn oil was added to both sauces as
well. But the sauce designed to produce lycopene in the bent molecular
forms was subjected to a second round of heating at 260 degrees
Fahrenheit for 40 minutes. The resulting sauce contained nine times
more cis-isomers than the regularly processed sauce.
Twelve people participated in a study of the sauces, and all ate
both kinds of sauce over the course of the study. After each meal,
researchers took samples of participants’ blood seven times during the
following 9 1/2 hours to measure lycopene levels. The scientists used a
special testing method to analyze lycopene levels in the blood
associated only with the tomato sauce meal, avoiding any other possible
sources of those compounds in the bloodstream.
Research participants had a 55 percent increase in total lycopene
absorption after eating the specially processed sauce when compared to
their lycopene blood levels after eating the regular sauce. This
finding reinforced the expectation that the bent forms of lycopene are
more easily absorbed into human blood, Schwartz said.
Details of this study were first published in the British Journal of
Nutrition in 2007. Additional clinical trials are ongoing.
Schwartz said most currently available commercial products don’t
contain the bent forms of lycopene molecules. But he noted that some
home cooking practices might be able to produce the same results as the
special processing method he and colleagues designed.
"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. 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," Schwartz said. "So it’s possible people could
induce this process and increase lycopene absorption by routine food
preparation procedures, as well."
Source : Ohio State University. August 2008.