May 17, 2010 — A University of
Illinois study has demonstrated that agronomic practices can greatly increase
the cancer-preventive phytochemicals in broccoli and tomatoes.
“We enriched pre-harvest 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 per cent of
• Standard broccoli.
• Standard tomato.
• Lycopene-enriched tomato.
• Tomato enriched with lycopene and
• Broccoli sprouts, which contain
very high levels of cancer-fighting compounds.
• Broccoli grown on soil treated
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
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 colour, 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.
“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,”
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.
Phyllis Picklesimer is a
communications specialist with the University of Indiana.