A University of Illinois study has demonstrated that agronomic
practices can greatly increase the cancer-preventive phytochemicals in
broccoli and tomatoes.
"We enriched preharvest broccoli with different bioactive components,
then assessed the levels of cancer-fighting enzymes in rats that ate
powders made from these crops," said Elizabeth Jeffery, a U of I
professor of food science and human nutrition.
The highest levels of detoxifying enzymes were found in rats that ate
selenium-treated broccoli. The amount of one of the cancer-fighting
compounds in broccoli was six times higher in selenium-enriched broccoli
than in standard broccoli powder, she said.
Selenium-treated broccoli was also most active in the liver, reaching
a level of bioactivity that exceeded the other foods used in the
experiment. "We were intrigued to find that selenium initiated this amount of bioactivity," she said.
Along with garlic and other plants of the allium family, broccoli and
other plants of the brassica family are unique in having a methylating
enzyme that enables plants to store high concentrations of selenium, she
said.
"Our bodies need a certain amount of selenium, but many areas of the
world, including parts of the United States and vast areas of China,
have very little selenium in the soil," she said.
"Not only could selenium in broccoli deliver this necessary mineral,
it also appears to rev up the vegetable's cancer-fighting power," she
added.
Jeffery is now working to determine whether selenium compounds are
directly responsible for the increase in bioactivity or if selenium acts
indirectly by directing new synthesis of the broccoli bioactives called
glucosinolates.
In a previous study, Jeffery and U of I colleague John W. Erdman Jr.
showed that tomato and broccoli powders eaten together are more
effective in slowing prostate cancer in laboratory rats than either
tomato or broccoli alone.
In their current research, they are experimenting with ways to
increase the bioactive components in these foods in order to test the
efficacy of enriched broccoli and tomatoes in a new prostate cancer
study.
Rats were fed diets with food powders containing 10 percent of either
standard broccoli; standard tomato; lycopene-enriched tomato; tomato
enriched with lycopene and other carotenoids; broccoli sprouts, which
contain very high levels of cancer-fighting compounds; or broccoli grown
on soil treated with selenium.
The scientists found that greater amounts of bioactive components in
the food powders translated into increased levels of the compounds in
body tissue and increased bioactivity in the animals.
Carotenoid-enriched tomatoes produced more bioactivity in the liver
than lycopene-enriched or standard tomatoes, yielding the most
cancer-preventive benefits. "Carotenoids, which are phytochemical pigments found in fruits and
vegetables, are thought to be excellent antioxidants and effective in
cancer prevention," said Ann G. Liu, a U of I graduate student who
worked on the study.
"A good rule is: the brighter the color, the higher the carotenoid
content. If you're growing or buying tomatoes, select plants or produce
that are a very bright red. High-lycopene tomatoes are now available
through garden catalogs," she added.
"This research shows that you can greatly increase a food's bioactive
benefits through normal farming practices, without resorting to genetic
engineering. Farmers have traditionally been more concerned about yield
than nutritional composition. Now we're asking, can we grow more
nutritional broccoli and tomatoes? And the answer is a definite yes,"
said Jeffery. The study was published in the Journal of Agricultural and Food Chemistry. Liu and Sonja E. Volker co-authored the paper with Jeffery and Erdman.
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