16 Agricultural Research/January 2004

Eggplant’sScientists Get Under Eggplant’sEggplant’s Skin

Agricultural Research Service scien-tists recently made headway unlockingthe secrets of Black Magic—a commer-cial eggplant cultivar representative ofU.S. market types. Apparently, whenhorticulturists named it, they were ontosomething. Turns out the variety hasnearly three times the amount of antiox-idant phenolics found in other eggplantcultivars that were studied.

Geneticist John R. Stommel of theARS Vegetable Laboratory and plantphysiologist Bruce D. Whitaker of theProduce Quality and Safety Laboratory,both in Beltsville, Maryland, haveteamed up to evaluate the amount of an-tioxidant phenolic compounds in a widevariety of eggplants. They’ve found thatdifferent genetic lines, or accessions,have dramatically different levels of phe-nolic acids—which in addition to hav-ing nutritive potential, give rise tobrowning of the fruit flesh once it is cut.Polyphenol oxidase is the enzyme thatmakes phenolics react to form brownpigments.

The team knew that some eggplantshad previously been found to be high inphenolic acids—a class of phenylpro-panoid compounds, such as flavonoids,that have a single phenyl ring and one tothree phenolic hydroxyls. Plants formthese compounds to protect against oxi-dative stress, as well as infection by bac-teria and fungi.

Rounding Up MethodsFirst, Whitaker established procedures

for analyzing the phenolic acids ineggplant—extracting them from egg-plant required care to avoid their oxi-dation. Once they were extracted, thescientists used three analytical meth-ods—HPLC, LC-MS, and NMR—toseparate, measure, and identify thecompounds.

The team began their study by usingthe methods to measure the phenolics inseven commercial varieties of eggplant.Then, they measured the levels and typesof phenolics in a broader test sample.

Technician Mindy Ehrenfried inspects fruit for harvest from one of the 115 accessions thatmake up the eggplant core collection. The peel of this white-fruited eggplant lacksanthocyanin pigments that give many eggplants their purple to black color.

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17Agricultural Research/January 2004

“We thought it would be useful to testthe potency of eggplant cultivars that arecommonly grown and consumed in thiscountry,” says Whitaker, “But we alsohoped to find traits from a broadergenetic sample that might be worthintroducing into popular commercialcultivars.”

Most people have probably tasted an eggplant. You may havebeen in an Italian restaurant where chefs use the purplish fruit (likea tomato, it is botanically classified as a fruit) in the popular disheggplant parmesan.

But maybe the eggplant used wasn’t purple.Maybe it wasn’t even teardrop shaped. Eggplantscome in hundreds of shapes and colors. But thefruit probably got its name because some small-fruited, white-pigmented eggplant varieties looklike chicken eggs.

Griffin, Georgia, is home to USDA’s eggplantcollection, which includes 770 different acces-sions collected from around the world. Whilenontraditional ones may not be available at most

grocery stores, they are often found in gourmet and ethnic foodstores and local farmers’ markets.

Eggplant is much more popular outside the United States,particularly in India (where the first eggplants supposedly grew)and other Asian countries. In India, manypeople eat small, round eggplants. Someenjoy eggplant cooked and served withother vegetables as part of a medley. Othersenjoy the popular dish of eggplant curry.Different ethnicities prefer differentvarieties, depending on how bitter they likethe fruit to taste.

Eggplant goes back about 2,000 yearsin the recorded history of India, and thereare actually more than 30 Sanskrit namesfor the fruit in ancient Indian literature.Thomas Jefferson is credited with bringingthe fruit to the United States.—By DavidElstein, ARS.

EveryoneKnowsWhat anEggplantIs...Right?

Geneticist John Stommel examines fruit ofa Solanum melongena, one of five speciesrepresented in the 115-accession eggplantcore collection. This commonly cultivatedspecies has the traditional dark fruit color.

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In preparation for analyzing antioxidantphenolic compounds, plant physiologistBruce Whitaker loads samples of eggplantextracts.

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Flowers of eggplant aresimilar to those of potatoand tomato. All threeplants are solanaceousspecies.

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18 Agricultural Research/January 2004

They turned to the ARS National PlantGermplasm Center (NPGC), located inGriffin, Georgia. NPGC’s mission is topreserve and characterize the germplasmof both cultivated and wild relatives ofparticular crops. Plant germplasm con-tains all the genetic information for aplant’s hereditary makeup. Such gene-banks are a rich source of plant materialthat can be used in developing improvedvarieties of crop plants.

NPGC gave the scientists seed sam-ples of 115 different types of eggplant.That group is known as the eggplant corecollection because it represents the ge-netic diversity of NPGC’s complete col-lection of more than 770 eggplantvarieties.

Some of NPGC’s eggplant germplasmwas collected from southeast Asia, andsome of the wild species came fromAfrica. Each had to be planted and grownbefore testing. “We were impressed withthe diversity we observed among plantswithin the collection,” says Stommel.“We found a wide variety of fruit shapes,sizes, and especially colors, includinggreen-, yellow-, and red-pigmented typesalong with the more common gradationsof black to purple.”

Finding Desirable TraitsFrom the study evaluating the 7

commercial cultivars, the team found 14phenolics—mostly derivatives of caffeicacid. “But there was a significant dif-ference in the content of these 14phenolics among fruit of the 7 cultivars,as well as in stem, middle, and blossom-end tissue segments from individualfruit,” says Whitaker.

Overall, the scientists found chloro-genic acid to be the predominant com-pound in all the samples analyzed. Thefinding is significant because chloro-genic acid and related esters of caffeicacid are among the most potent freeradical scavengers found in plant tissues.Benefits reported include antimutagenic,antimicrobial, anti-LDL, and antiviralactivities.

Still, while the studies conducted havehelped characterize the content of phe-nolic acids in various eggplant acces-sions, the scientists have more to learn.“We need to find out whether and howvarious phenolic acid levels affect fla-vor,” says Stommel.

The current evidence indicates thatphenolics in eggplants are good for peo-ple, but they may also impart a bittertaste. In theory, eggplants with the high-est level of antioxidants also taste themost bitter. In the future, the scientistswant to help define eggplants with anoptimal balance of phenolics to ensureboth high nutritional value and consum-er acceptance. “We don’t want to devel-op something that is so bitter that peoplewon’t like it,” says Stommel.

Picking ParentageAs 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 intocultivated varieties for health purposes.In the study involving the eggplant corecollection, two phenolic compounds thathad never before been identified in planttissue were found in a wild eggplant spe-cies. “We need to confirm the identity ofthese compounds with further analyses,”says Whitaker.

A consumer evaluation, together withdata from the larger study, could be usedin choosing parental lines for producingimproved varieties. The goal of such aprogram is to establish new breedinglines and then release them to the com-mercial seed industry for developmentof finished varieties that will benefit con-sumers.

“Ultimately, we want to help developeggplant cultivars with improved phenol-ic acid composition as well as improvedtaste,” says Stommel. This research willhelp identify desirable traits for cross-breeding—or what scientists callintrogressing—into existing adaptedgermplasm.

The findings were published in theJune 2003 issue of the Journal of Agri-cultural and Food Chemistry and theSeptember 2003 issue of the Journal ofthe American Society for HorticulturalScience.—By Rosalie Marion Bliss andDavid Elstein, ARS.

This research is part of Quality andUtilization of Agricultural Products(#306) and Genetic Improvement (#301),two ARS National Programs describedon 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, MD20705-2350; phone (301) 504-5583, fax(301) 504-5555, e-mail stommelj@ba.ars.usda.gov.

Bruce D. Whitaker is with the USDA-ARS Produce Quality and Safety Labo-ratory, 10300 Baltimore Ave., Bldg. 002,Beltsville, MD 20705-2350; phone (301)504-6984, fax (301) 504-5107, e-mailwhitakeb@ba.ars.usda.gov. ★

Technician Andrea Blas prepares samplesof eggplant for laboratory analysis ofphenolic acids.

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