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Researchers mind the mint.

Researchers Mind the Mint

From juleps to grasshopper pie, toothpaste to antacids--mint sparkles the flavor of our foods and our pharmacy items.

Mint's distinct, refreshing taste comes from volatile oils produced in tiny sacs in the leaves and stems of various Mentha species--Mentha piperita, or peppermint, being one of the most common.

Surprisingly, there are close to 500 different accessions--including chocolate mint, pineapple mint, eau de cologne mint, to name a few--at the National Clonal Germplasm Repository's collection of Mentha and Pycnanthemum (mountain mint).

Located in the heart of mint-growing country--Oregon's verdant Willamette Valley--the fragrant assemblage of mints is the largest in this country, and one of the most diverse worldwide, says Henrietta L. Chambers, who oversees the collection.

The mints are one of many different crops, including pears, most berries, hazelnuts, and hops, housed at the Corvallis, Oregon, repository.

The repository is one in a network of 30 ARS-managed gene banks that preserve economically important crops and their wild relatives.

These gene banks assure plant geneticists a ready source of material for breeding new crops to resist environmental stresses, such as insect pests or unfavorable weather. Another important function is to save rare species related to cultivated plants that might otherwise be lost due to livestock grazing and construction.

In the case of mint, however, several unusual applications of the collection have cropped up.

For instance, last year the National Cancer Institute in Bethesda, Maryland, requested samples of several Pycnanthemum species to screen them for anti-cancer or anti-AIDS properties. Recently, however, word came back that the findings were negative. "We were a bit disappointed, but we were glad to have used the collection in such a way," says Chambers.

Yet Pycnanthemum species may offer hope for other, less serious but still troublesome problems, according to James Duke, a botanist with the ARS Germplasm Resources Laboratory in Beltsville, Maryland. Mountain mint, pennyroyals and Hedeoma pulegioides, and corn mint, all contain high levels of pulegone, a compound that repels fleas, ticks, and mosquitoes. Certain ticks carry organisms responsible for Lyme disease and Rocky Mountain spotted fever, Duke points out.

Other compounds in Pycnanthemum and Mentha, namely menthol and menthone, may help alleviate decompression syndrome and altitude sickness, problems that plague scuba divers and mountain climbers. A 1986 study showed that the compounds help prevent the cause of both ailments--the aggregation of blood components called platelets.

Mints might help solve economics as well as medical problems. Because it's a relatively high-value crop (the oil is worth between $15 and $25 a pound), ARS scientists consider mint a possible alternative crop for Bolivian peasants who farm coca in the Andean foothills.

In 1990, Chambers sent six mint accessions to a scientist at an agriculture development program affiliated with San Simon University in Cochabamba, Bolivia. Included was a genotype grown in Brazil that could feasibly also thrive in Bolivia. For now, however, it's still too early to comment on mint's success, says George A. White of ARS' National Germplasm Resources Laboratory, who supervises international germplasm distribution.

No matter where it's grown, mint shows up in cuisines throughout the world. A fresh mint sprig makes an attractive garnish on any plate. The fragrant herb also appears often in Indian, Thai, and other Middle Eastern dishes, either sauteed with meats or minced fresh in salads.

Mint oils, however, are much more widely used, particularly in America and European countries. Probably the most familiar uses of mint flavorings are in chewing gum and toothpaste. But it's found throughout the medicine chest--in mouthwash, antacids, even shaving cream. Cough drops sometimes contain one of mint's chief volatile oils, menthol.

Many noncaffeinated or herbal tea blends include dried peppermint or spearmint leaves. And the Oregon Mint Snuff Co. sells dried mint leaves as a substitute for chewing tobacco. The all-mint chew is billed as a nonharmful alternative to smokeless tobacco, the use of which has been linked with oral cancer.

Mints may have a place in your garden as well as in your home--some are attractive ornamentals. For example, the low-growing Corsican mint, native to that Mediterranean island and others, makes a soft, mosslike carpet that will spread to fill in cracks between a rock path.

"When you walk on it, you'll notice a nice, fresh mint aroma," says Chambers. While the plants may die back over the winter in colder climates, they revive in spring and aren't bothered by foot traffic.

Pineapple mint, sporting light green leaves with white edges, also makes a nice ornamental, as does a variegated (green and white) peppermint. And there is the round-leafed Mentha sauveolens, or apple mint, which, according to Chambers, really does have an apple fragrance.

For a citruslike scent, there's an orange mint. And chocolate mint is a nursery favorite, accoring to Bob Hornback, manager of the Ya-Ka-Ama Nursery in Forestville, California, which retails over 15 to 20 different mint varieties.

Hornback admits that the chocolate smell is "more in the imagination of the beholder," adding that he thinks of chocolate peppermint patties.

The plant's stems are a deep chocolate brown color, rather than the reddish brown of most other peppermints, says Chambers, who herself conjures up visions

of chocolate mint Girl Scout cookies.

What about the eau de cologne mint? "It has a smell reminiscent of lavender," says Chambers.

Each variety, along with many other accessions, grows in 6-inch pots in a screenhouse. The screenhouse excludes insects like whiteflies that may transmit viruses or bees that may pollinate the mint flowers.

While most of the accessions originated in Europe, others come from elsewhere around the globe--Japan, Morocco, Pakistan, and Russia. Chambers hopes to visit New Zealand and Australia to collect mints native to those countries.

"There are wid mints growing in Australian grasslands we'd especially like to have--there's heavy livestock grazing in those areas that could wipe out certain species," she says.

The Mentha genus, Chambers points out, is just one among 180 different genera in the broader mint family, Labiatae. Other well-known mint family members include many culinary herbs such as basil, marjoram, and oregano, as well as catnip and lavender.

Salient features that identify mint, notes Chambers, are plants with a distinctive (not always pleasant) scent, and leaves that grow in pairs opposite each other on a square stem.

Most mints display spikes of white or pale lavender flowers with tiny purple spots. Chambers uses these flowers in the further evaluation of the collection--counting the chromosomes in cells that develop into pollen.

She first pickles, or preserves, the tiny mint flower buds in a mixture of chloroform, alcohol, and acetic acid. The solution pulls water from the plant's cells but leaves them otherwise intact.

Next she squashes the flower's anthers--where pollen formation takes place--and stains them for viewing under the microscope. She can then observe meiosis, the cell division that gives rise to the pollen, the plant's male sex cells. Because they will later fuse with the female sex cell, or egg, the pollen grains (like the egg) contain only half the chromosome set and are thus easier to count than other cells, which contain the double set. Mints have between 18 and 144 chromosomes, says Chambers.

Some mints have three, rather than two sets of chromosomes. These triploid plants are sterile, because the third chromosome set can't pair properly. Mint farmers require sterile plants, because mints, like all clonally propagated plants, produce seeds that are genetically different from the original plant. Farmers can't have these other mints contaminating their stands, since mint processors demand pure oil from a single genotype.

Peppermint, Chambers points out, is actually a hybrid species--an ancient cross between spearmint (M. spicata) and M. aquatica, a broadleafed mint that doesn't have an especially good fragrance.

The most popular northwestern cultivars are Mitcham peppermints, named after a town near London, where they were first collected. Native spearmint and Scotch spearmint are also grown.

Mint harvesting begins in mid to late summer, when the plants are 2-3 feet tall. Farmers cut plants close to the ground, leaving them in windrows--heaps of hay left in the field to dry for a few days. Afterwards, the mint is steam-distilled to extract the oil.

Oregon leads the nation in mint oil production, followed by Washington and Idaho. Smaller amounts grow in Montana, Michigan, Indiana, South Dakota, and Wisconsin.

Growers sell the oil by the barrel to various companies, such as Wrigley's and Palmolive, whose scientists then blend different batches of oil to achieve a desired flavor or scent. According to the Oregon Mint Commission, a pound of mint oil can flavor 45,000 sticks of gum.

PHOTO : Horticulturist Henrietta Chambers plots the distribution of New Zealand mentha. (K-4424-5)

PHOTO : An assortment from the mint collection: (top to bottom) solid-green orange mint, variegated pineapple mint, fine-leafed Corsican mint, and peppermint. (K-4424-4) (K-4424-2)

Henrietta L. Chambers is with the USDA-ARS National Clonal Germplasm Repository, 33447 Peoria Rd., Covallis, OR 97333. Phone (503) 757-4448.
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Author:Corliss, Julie
Publication:Agricultural Research
Date:Jan 1, 1992
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