Scientists Get Under Eggplant's Skin
Ehrenfried inspects fruit
for harvest from one of
the 115 accessions that make
up the eggplant core
collection. The peel of
this white-fruited eggplant
lacks anthocyanin pigments
that give many eggplants
their purple to black color.
Agricultural Research Service
scientists recently made headway unlocking the secrets of Black Magica
commercial eggplant cultivar representative of U.S. market types. Apparently,
when horticulturists named it, they were onto something. Turns out the
variety has nearly three times the amount of antioxidant phenolics found
in other eggplant cultivars that were studied.
Geneticist John R. Stommel of the ARS Vegetable Laboratory and plant
physiologist Bruce D. Whitaker of the Produce Quality and Safety Laboratory,
both in Beltsville, Maryland, have teamed up to evaluate the amount
of antioxidant phenolic compounds in a wide variety of eggplants. They've
found that different genetic lines, or accessions, have dramatically
different levels of phenolic acidswhich in addition to having
nutritive potential, give rise to browning of the fruit flesh once it
is cut. Polyphenol oxidase is the enzyme that makes phenolics react
to form brown pigments.
The team knew that some eggplants had previously been found to be high
in phenolic acidsa class of phenylpropanoid compounds, such as
flavonoids, that have a single phenyl ring and one to three phenolic
hydroxyls. Plants form these compounds to protect against oxidative
stress, as well as infection by bacteria and fungi.
Geneticist John Stommel
examines fruit of a
one of five species
represented in the
core collection. This
commonly cultivated species
has the traditional dark
Rounding Up Methods
First, Whitaker established procedures for analyzing the phenolic acids
in eggplantextracting them from eggplant required care to avoid
their oxidation. Once they were extracted, the scientists used three
analytical methodsHPLC, LC-MS, and NMRto separate, measure,
and identify the compounds.
The team began their study by using the methods to measure the phenolics
in seven commercial varieties of eggplant. Then, they measured the levels
and types of phenolics in a broader test sample. "We thought it
would be useful to test the potency of eggplant cultivars that are commonly
grown and consumed in this country," says Whitaker, "But we
also hoped to find traits from a broader genetic sample that might be
worth introducing into popular commercial cultivars."
They turned to the ARS National Plant Germplasm Center (NPGC), located
in Griffin, Georgia. NPGC's mission is to preserve and characterize
the germplasm of both cultivated and wild relatives of particular crops.
Plant germplasm contains all the genetic information for a plant's hereditary
makeup. Such genebanks are a rich source of plant material that can
be used in developing improved varieties of crop plants.
In preparation for analyzing
antioxidant phenolic compounds,
plant physiologist Bruce
Whitaker loads samples of
NPGC gave the scientists seed samples of 115 different types of eggplant.
That group is known as the eggplant core collection because it represents
the genetic diversity of NPGC's complete collection of more than 770
Some of NPGC's eggplant germplasm was collected from southeast Asia,
and some of the wild species came from Africa. Each had to be planted
and grown before testing. "We were impressed with the diversity
we observed among plants within the collection," says Stommel.
"We found a wide variety of fruit shapes, sizes, and especially
colors, including green-, yellow-, and red-pigmented types along with
the more common gradations of black to purple."
Finding Desirable Traits
From the study evaluating the 7 commercial cultivars, the team found
14 phenolicsmostly derivatives of caffeic acid. "But there
was a significant difference in the content of these 14 phenolics among
fruit of the 7 cultivars, as well as in stem, middle, and blossom-end
tissue segments from individual fruit," says Whitaker.
Technician Andrea Blas prepares
samples of eggplant for
laboratory analysis of
Overall, the scientists found chlorogenic acid to be the predominant
compound in all the samples analyzed. The finding is significant because
chlorogenic acid and related esters of caffeic acid are among the most
potent free radical scavengers found in plant tissues. Benefits reported
include antimutagenic, antimicrobial, anti-LDL, and antiviral activities.
Still, while the studies conducted have helped characterize the content
of phenolic acids in various eggplant accessions, the scientists have
more to learn. "We need to find out whether and how various phenolic
acid levels affect flavor," says Stommel.
The current evidence indicates that phenolics in eggplants are good
for people, but they may also impart a bitter taste. In theory, eggplants
with the highest level of antioxidants also taste the most bitter. In
the future, the scientists want to help define eggplants with an optimal
balance of phenolics to ensure both high nutritional value and consumer
acceptance. "We don't want to develop something that is so bitter
that people won't like it," says Stommel.
As the scientists learn more about the genetic traits of the various
accessions, they expect that traits from some of the wild species may
eventually be bred into cultivated varieties for health purposes. In
the study involving the eggplant core collection, two phenolic compounds
that had never before been identified in plant tissue were found in
a wild eggplant species. "We need to confirm the identity of these
compounds with further analyses," says Whitaker.
A consumer evaluation, together with data from the larger study, could
be used in choosing parental lines for producing improved varieties.
The goal of such a program is to establish new breeding lines and then
release them to the commercial seed industry for development of finished
varieties that will benefit consumers.
"Ultimately, we want to help develop eggplant cultivars with improved
phenolic acid composition as well as improved taste," says Stommel.
This research will help identify desirable traits for cross-breedingor
what scientists call introgressinginto existing adapted germplasm.
The findings were published in the June 2003 issue of the Journal
of Agricultural and Food Chemistry and the September 2003 issue
of the Journal of the American Society for Horticultural Science.By
Rosalie Marion Bliss
and David Elstein, Agricultural
Research Service Information Staff.
This research is part of Quality and Utilization of Agricultural
Products (#306) and Genetic Improvement (#301), two ARS National Programs
described on the World Wide Web at www.nps.ars.usda.gov.
John R. Stommel is
with the USDA-ARS Vegetable
Laboratory, Bldg. 010A, 10300 Baltimore Ave., Beltsville, MD 20705-2350;
phone (301) 504-5583, fax (301) 504-5555.
Bruce D. Whitaker
is with the USDA-ARS Produce
Quality and Safety Laboratory, 10300 Baltimore Ave., Bldg. 002,
Beltsville, MD 20705-2350; phone (301) 504-6984, fax (301) 504-5107.
What an Eggplant Is...Right?
Most people have probably tasted an eggplant. You may have been in
an Italian restaurant where chefs use the purplish fruit (like a tomato,
it is botanically classified as a fruit) in the popular dish eggplant
But maybe the eggplant used wasn't purple. Maybe it wasn't even teardrop
shaped. Eggplants come in hundreds of shapes and colors. But the fruit
probably got its name because some small-fruited, white-pigmented eggplant
varieties look like chicken eggs.
Griffin, Georgia, is home to USDA's eggplant collection, which includes
770 different accessions collected from around the world. While nontraditional
ones may not be available at most grocery stores, they are often found
in gourmet and ethnic food stores and local farmers' markets.
Flowers of eggplant are similar
to those of potato and tomato.
All three plants are
| Eggplant is much more popular
outside the United States, particularly in India (where the first eggplants
supposedly grew) and other Asian countries. In India, many people eat
small, round eggplants. Some enjoy eggplant cooked and served with other
vegetables as part of a medley. Others enjoy the popular dish of eggplant
curry. Different ethnicities prefer different varieties, depending on
how bitter they like the fruit to taste.
Eggplant goes back about 2,000 years in the recorded history of India,
and there are actually more than 30 Sanskrit names for the fruit in
ancient Indian literature. Thomas Jefferson is credited with bringing
the fruit to the United States.By David Elstein, Agricultural
Research Service Information Staff.
"Scientists Get Under Eggplant's Skin" was published
in the January
2004 issue of Agricultural Research magazine.