Geneticist Linda Pollak (left)
and plant biologist Susan
Duvick inspect seed
characteristics of Tripsacum-
introgressed corn, which
has high levels of oleic acid.
New corn varieties bred by scientists at the Agricultural
Research Service and Iowa State University (ISU) may just do one's
heart some good.
In fact, the 14 new lines may lead to a slew of desirable
corn-based products, like cooking oils and margarine that keep blood
cholesterol levels down or salad dressings that last longer. They may
even lead to less-expensive animal feed.
ARS geneticist Linda Pollak and plant biologist Susan Duvick, along with ISU food science professor Pamela White, have crossed traditional Corn Belt inbred lines with varieties cultivated during past independent studies that contain genes from eastern gamagrass, Tripsacum dactyloides.
Geneticist Susan Duvick (left)
and ISU food science professor
Pamela White examine a vial
of oil extracted from
corn before loading it into
the autosampler for analysis
by gas chromatography.
Pollak works at the ARS Corn Insects and Crops Genetics Research Unit, while Duvick works at the ARS North Central Regional Plant Introduction Station, both on the ISU campus in Ames.
"One of the great things about these lines,"
says Duvick, "is that they were developed through traditional plant
breeding. As a result, they can have a lot of applications in markets
that are resistant to biotechnology."
The most promising of these "Tripsacum-introgressed
lines," as the researchers call them, are ones with high percentages
of oleic acid. This monounsaturated fatty acid may be the key to "heart-friendlier"
Duvick says high percentages of oleic acid "give
corn oil stability with regard to flavor and deterioration and have
also been linked to lowering blood cholesterol levels in people."
High levels of cholesterol in the blood can lead to coronary heart disease,
heart attacks, and stroke.
There are three basic fatty acid types. "Saturated
fatty acids have great stability. Thus oils and products made with a
high percentage of them have long shelf lives and can endure the heat
of deep-fat frying without breaking down," says White. Their main
drawback? They raise blood cholesterol levels.
The second type, polyunsaturated fatty acids, have been
linked to lower incidences of heart disease. But they lack strong stability
traits. They are also prone to oxidation and development of unstable
molecules called free radicals, which are associated with a higher risk
of cancer. Free radicals can be very destructive to human tissue.
Says White, "As a monounsaturated fatty acid, the
third type, oleic acid has higher stability than the polyunsaturated
acids. And it has good characteristics, similar to those of the polyunsaturated
fatty acids, when it comes to prevention of cholesterol and heart disease."
These features may be a boon to producers of corn-based
cooking oils, who have lost customers to high-oleic alternatives such
as olive oil and canola oil.
"A high-oleic oil contains a lower percentage of the other types of fatty acids," says White. "That means you get fewer negative effects of either polyunsaturated or saturated fatty acids while maintaining their many good properties."
What's So Special About High-Oleics?
"A high-oleic oil may also help reduce plasma levels of low-density
lipoproteinsor 'bad' cholesterolwithout reducing the high-density
lipoproteinsor 'good' cholesterol," adds White.
High-oleic corn oil also provides good starting material for making
margarine. That's because replacing polyunsaturated fatty acids with
oleic acid could mean that less processing is needed to create the hardened
but spreadable product.
Most margarine is made of highly polyunsaturated fats. They gain stability
and consistency through hydrogenation, a process during which hydrogen
atoms are forced into unsaturated fatty acids. This process creates
trans fatty acids, which many consider to be cholesterol-raising compounds.
But Pollak warns that high percentages of oleic acid will not eliminate
margarine-related heart health issues, adding, "This is still a
high-fat food that must be consumed in moderation."
Oleic acid's stability, which makes for longer storage and refrigerator
shelf life, may also prove attractive to makers of salad dressing. "Many
salad dressings today use very polyunsaturated soybean or canola oils,
which don't have high stability and thus can become rancid relatively
quickly," says White.
She adds that some salad dressing makers use oils that have been partially,
or lightly hydrogenated, a process that can be sidestepped by using
oil high in oleic acid.
Pollak says some Tripsacum lines that have high protein and oil content can lead to cost-effective animal feeds, which could enable ranchers to reduce or bypass expensive soybean meal.
A Long Time Evolving
The new varieties can be traced to corn evolution studies during the
1970s at the University of Illinois. They produced corn populations
that were infused with genes from eastern gamagrass, a wild, native
grass species distantly related to corn. Gamagrass was used because
it resists cold and insects and tolerates both drought and flooding.
These traits would be desirable in corn hybrids.
Duvick became interested in the hybrids while conducting research during
the early 1990s at ARS' Southern Plains Research Station in Woodward,
Oklahoma, and brought samples back to her lab to experiment with. The
Oklahoma researchers were using them in forage-improvement studies.
Duvick, Pollak, and White have submitted a patent application (No.
09/285,368) for the Tripsacum-introgressed corn lines, and they
currently seek commercial partners. "Seed companies and firms developing
new corn breeding lines could use this technology, as could companies
in the food or feed industries," says Pollak.
Duvick says some of the new lines yield oils containing 60 to 70 percent
oleic acid, compared to the 20 to 30 percent rate found in commercially
available corn oils. She adds that varieties have been developed that
have oils with total saturated fatty acid composition as low as 6.5
percentcompared to the 13 percent found in corn oils currently
Pollak says future research on the subject will focus on two areas:
examining the types of products that can use the high-oleic lines and
crossing the new lines with existing corn varieties.By Luis
Pons, Agricultural Research Service Information Staff.
This research is part of Plant, Microbial, and Insect Genetic Research,
Genomics, and Genetic Improvement, an ARS National Program (#301) described
on the World Wide Web at www.nps.ars.usda.gov.
Linda M. Pollak is in
the USDA-ARS Corn
Insects and Crops Genetics Research Unit, and Susan
A. Duvick is with the USDA-ARS North
Central Regional Plant Introduction Station, Agronomy Building,
Iowa State University, Ames, IA 50011-0000; [Pollak] phone (515) 294-7831,
fax (515) 294-9359, [Duvick] phone (515) 294-9375, fax (515) 294-4880.
"Heart-Friendly Corn Oil? New High-Oleic Corn Varieties Make It Possible" was published in the August 2003 issue of Agricultural Research magazine.