...From the pages of Agricultural Research magazine
ARS researchers have selectively
bred carrots with pigments
that reflect almost all colors
of the rainbow. More importantly,
though, they're very good for
Shredded in salads and slaws, steamed, or just peeled and dunked in
an herb-speckled dip, carrots are versatile veggies that add colorful
zest to our dinner plates. These crunchy orange roots are also a well-known
source of vitamin A. Just a single, full-size carrot more than fulfills
an adult's daily quotient of the essential vitamin.
But the carrot hasn't always been the vitamin A powerhouse that it is today. Over two decades ago, scientists in the ARS Vegetable Crops Research Unit at Madison, Wisconsin, began a quest to breed carrots packed with beta-carotenean orange pigment used by the body to create vitamin A. Thanks largely to this ARS work, today's carrots provide consumers with 75 percent more beta-carotene than those available 25 years ago.
Cross-sections of the
highly pigmented carrots.
The researchers, led by plant geneticist Philipp Simon, haven't limited themselves to the color orange. They've selectively bred a rainbow of carrotspurple, red, yellow, even white. Scientists are learning that these plant pigments perform a range of protective duties in the human bodywhich is not surprising, says Simon, since many of the pigments serve to shield plant cells during photosynthesis.
Red carrots derive their color mainly from lycopene, a type of carotene
believed to guard against heart disease and some cancers. Yellow carrots
accumulate xanthophylls, pigments similar to beta-carotene that support
good eye health. Purple carrots possess an entirely different class
of pigmentsanthocyaninswhich act as powerful antioxidants.
While colored carrots are unusual, they're not exactly new. "Purple
and yellow carrots were eaten more than 1,000 years ago in Afghanistan
and 700 years ago in western Europe," says Simon. "But the
carrot-breeding process has gone on intensively for just 50 years."
Simon and his team of ARS researchers and colleagues at the University of Wisconsin-Madison (UW) have recently shown that their highly pigmented carrots are a ready source of some sought-after nutrients.
The Eyes Have It
Lutein is one of the hydroxy carotenoids that make up the macular pigment
of human retinas. Consuming foods high in lutein may increase the density
of this pigment and decrease the risk for developing macular degeneration,
an age-related disease.
"Up to now," says Simon, "we didn't know whether lutein
was biologically available from carrots, because they're considered
a complex food."
In a study to determine humans' lutein uptake from lutein-rich yellow
carrots, Simon, along with UW's Sherry Tanumihardjo, recruited nine
23- to 28-year-old volunteers to eat the carrots and take a lutein supplement.
By reading the participants' blood serum levels, the researchers found
that lutein from the carrots was 65 percent as bioavailable as it was
from the supplement.
Tanumihardjo, an assistant professor in UW's Department of Nutritional
Sciences, says, "While other foods might contain higher levels
of luteinlike spinach for instancelutein is absorbed very
well from lutein-rich carrots."
In another study, Simon and Tanumihardjo found that lycopene from red-pigmented
carrots is 40 percent as bioavailable as it is from tomato paste. "Not
everyone eats or likes tomatoes," she says, "so finding another
source of lycopene that also provides beta-carotene is very positive."
Their lycopene study appeared in the May 2004 issue of the European Journal of Clinical Nutrition. The lutein study appeared in the July 2004 issue of the American Journal of Clinical Nutrition.
Behind the Colors
In nature, different strains of carrots contain varying types and amounts
of carotenoidsthe pigments responsible for orange, yellow, and
red colors. To assist seed companies and growers who wish to produce
nutrient-rich carrots, Simon and his lab are working to map all the
genes that play a part in synthesizing carotenoids in major carrot lines.
Simon now knows of 20 genes that are involved. But determining a particular
gene's role in generating carotenoids is not that straightforward.
"There are complexities in reading these genes," he says, "since their functions often change with the plant as it progresses through its life cycle." From Simon's work, it appears that two or three major genes account for differences in white and orange carrots and that another couple of genes separate yellow carrots from red.
Why Be Conventional?
What would you say to a glass of purple carrot juice? Some aren't so
Aside from enhancing the nutritional value of carrotsas well
as onions, garlic, and cucumbersresearchers at Simon's laboratory
also work to improve the veggies' culinary quality and appeal.
"It's hard to know what to aim for when selecting for a purple
carrot," Simon says, "since we've no defined type to go by."
So he's subjecting the new varieties to consumer taste tests, hoping
to find carrots with a sweet and mild flavor.
"People who are asked to taste the colorful carrots are concerned
about their flavor," says Simon. "We've become married to
the colors we associate with particular foods. We eat with our eyes,
to some extent."
Tanumihardjo agrees. "I did a study to find out whether carrot
color prompted perception of taste at all," she says. "When
people were able to see the color of the carrotwhether it was
purple or redthey responded more favorably to it."
With the help of Tanumihardjo, Simon is tapping taste preferences through
an unexpected group of eaters: children in Wisconsin's inner cities
and American Indian reservations. Children from lower income groups
are at greater risk for developing a nutritional deficiency, like low
vitamin A status. "Some of these kids have never even had a carrot
before," says Simon. But their comments so far have been positive,
according to Tanumihardjo.
With their compelling health benefits and a thumbs-up from taste testers,
Simon's colorful carrots will be a great addition to supermarket produce
aisles once consumers create a demand for them.By Erin
K. Peabody, formerly with Agricultural Research Service Information Staff.
This research is part of Plant, Microbial, and Insect Genetic Resistance,
Genomics, and Genetic Improvement, an ARS National Program (#301) described
on the World Wide Web at www.nps.ars.usda.gov.
"Carrots With Character" was published in the November 2004 issue of Agricultural Research magazine.