A. Essential Oils Smaller, monoterpenes and sesquiterpenes that are volatile at room temperature. They occur in leaves, flowers and fruits, often imparting a distinctive odor and flavor. Note: Some essential oils include phenolic compounds and terpene-phenolic derivatives. Phenolic compounds typically contain one or more benzene rings with one or more hydroxyl groups (C-OH) attached to the rings. Essential oils serve several functions in plants, such as repelling fungi and harmful insects, and the sweet fragrances of flowers that attract insect pollinators. The 10-carbon monoterpene limonene is enantiomorphic and occurs in two mirror image forms called stereoisomers. Fragrant D-limonene found in citrus peels is an effective insect repellant and insecticide. Known as "orange oil" it is readily absorbed into wood and is used to exterminate dry wood termites. It is much safer than methyl bromide gas and doesn't require the tenting and evacuation of houses. It is a good solvent for grease and is a common ingredient of orange-scented hand soaps and cleaners. Lemon oil from the rind of lemons is approximately 90 percent D-limonene. In contrast to the citrus scent of D-limonene, the enantiomer L-limonene has a piney, turpentine-like odor. It occurs naturally in essential oils of pine and other conifers, certain herbs (e.g. peppermint and spearmint), and as a minor component of raw turpentine.
| Two-dimensional structural formulas for the stereoisomers of limonene (L-limonene & D-limonene). Like right and left-hand gloves, the molecules are exact mirror images. Their three-dimensional molecular shapes cannot be superimposed over each other. They both have the same empirical formula with 10 atoms of carbon and 16 atoms of hydrogen: C10H16 |
1. Herbs: Herbaceous plants mostly from temperate regions, particularly in the mint, carrot and sunflower families. Some representative herbs of the mint family (Lamiaceae) include basil (Ocimum basilicum), rosemary (Rosmarinus officinalis), thyme (Thymus vulgaris), sage (Salvia officinalis), peppermint (Mentha piperita), spearmint (M. spicata), oregano (Origanum vulgare), horehound (Marrubium vulgare) and catnip (Nepeta cataria). The terpene in catnip (nepetalactone) is a methylcyclopentane monoterpene that for some reason is very attractive to members of the cat family (Felidae). Herbs of the carrot family (Apiaceae) include parsley (Petroselinium crispum), coriander seeds & cilantro leaves (Coriandrum sativum), caraway (Carum carvi), dill (Anethum graveolens), anise (Pimpinella anisum), fennel (Foeniculum vulgare) and cumin (Cuminum cyminum). Some herbs of the sunflower family (Asteraceae) include tarragon (Artemisia dracunculus), chamomile (Anthemis nobilis) and German chamomile (Matricaria chamomilla). There are many other plant families with species containing essential oils. For example, the myrtle family (Myrtaceae) includes eucalyptol from (Eucalytus globulus), citronellal from (E. citriodora) and eugenol from species of Eugenia (Syzygium). Remember that some of these aromatic essential oils are phenolic compounds rather than terpenes. For more information refer to Wayne's Word Economic Plant Families.
2. Spices: Like herbs, spices are used to enhance the flavors of foods, but unlike most herbs, spices are generally tropical in origin and are usually more expensive. In fact, the famous voyages of explorers such as Marco Polo, Vasco de Gama, Christopher Columbus and Sir Francis Drake were (at least in part) in search of valuable spices. The aroma and tantalizing flavor of some spices is due to volatile phenolic compounds and alkaloids, in addition to terpenes. Some of the world's most important spice plants include ginger (Zingiber officinale), cardamom (Elettaria cardamomum) and turmeric (Curcuma domestica, all members of the ginger family (Zingiberaceae); black pepper (Piper nigrum, Piperaceae), nutmeg and mace (Myristica fragrans, Myristicaceae), cloves from unopened flower buds of Syzygium aromaticum (Myrtaceae), and cinnamon from the bark of Cinnamomum zeylanicum (Lauraceae). [The Mediterranean herb called capers (Capparis spinosa, Capparaceae) is also from flower buds.] Allspice comes from the dried, green berries of Pimenta dioica, a central American tree of the myrtle family (Myrtaceae). It is also known as pimento; however, the red pimentos that are stuffed into green olives are actually a variety of sweet chile pepper (Capsicum annuum) that belongs to the nightshade family (Solanaceae). The name "allspice" refers to the flavor of the berries, which resemble a combination of cinnamon, nutmeg and cloves. Red chile peppers and bell peppers are from species of Capsicum, New World plants in the nightshade family (Solanaceae). Red peppers were discovered by Columbus in the West Indies while en route to the East Indies. The name pepper was used by the Spanish, who were hoping to find the true spice pepper of the East Indies. Chile peppers will be discussed in more detail under alkaloids. Vanilla comes from the seed capsule of the vanilla orchid (Vanilla fragrans), the only commercially important product in the Orchidaceae, the second largest plant family. Most vanilla flavorings sold in markets are synthetic vanillin containing artificial food coloring & preservatives. Vanillin is a phenolic compound derived from the breakdown of lignin, a complex phenolic polymer that gives seasoned wood its color, hardness and mass. For more information about spices refer to Wayne's Word Economic Plant Families.
3. Perfumes: A large group of sweet, aromatic terpenes produced by many species in diverse plant families. Some of these compounds contain aldehyde groups, and some are phenolic essential oils. One of the most obvious adaptive advantages of perfumes is to provide flowers with fragrant scents that attract insect pollinators. The distillation of these fragrant compounds by people, and the ancient art of perfumery dates back to the beginning of recorded history. Plants grown for their unique essential oils include Rosa damascena (Rosaceae), Jasminum grandiflorum (Oleaceae), Pelargonium spp. (Geraniaceae), Gardenia spp. (Rubiaceae), and Viola odorata(Violaceae). Lavender comes from the species of Lavandula in the mint family (Lamiaceae). Orange blossom perfume comes from Citrus aurantium and bergamot is from the fruit rinds of C. bergamia (C. aurantium ssp. bergamia), two members of the citrus family (Rutaceae). Saffron is a yellowish-orange dye that is used in medicinals, as a flavoring, and in perfumes. It is obtained from the stigmas of Crocus sativus of the iris family (Iridaceae). The coloring principle is crocin, a tetraterpene carotenoid pigment related to vitamin A. It takes about 4,000 stigmas to yield one ounce of the dye, and one part of commercial saffron is sufficient to color 10,000 parts of water. Because of their volatile, strongly-scented terpene component, balsam oleoresins from several species of trees are also used in perfumes, incenses and medicines. Resins are discussed in the next section.
|
| B. Resins: Plant exudates containing nonvolatile 20-carbon diterpenes and 30-carbon triterpenes that are insoluble in water but soluble in organic solvents. [Have you ever tried to wash pine pitch off your hands in water?] Oleoresins (oleo referring to the essential oil component) contain nonvolatile terpenes plus volatile 10-carbon monoterpenes and 15-carbon sesquiterpenes. Resins are generally produced by cells lining resin ducts or canals in stems and leaves. Resins repel insects (such as bark beetles), deter vertebrate herbivores, and inhibit the growth of fungi and bacteria. Exuded resins aid in the healing of wounds and prevent desiccation. The resin glob at left came from the trunk of the Australian bunya-bunya (Araucaria bidwillii). |
The leaves of some desert shrubs, such as creosote bush (Larrea tridentata) have a glistening resinous coating that reduces water loss through transpiration. Although it has a similar odor, this resin is not the commercial source of creosote. The commercial source of creosote is derived from the distillation of coal tar. It is produced by high temperature carbonization of bituminous coal. Wood creosote is obtained from the distillation of wood tar from several woods of the eastern United States. Wood creosote is a mixture of phenolic compounds that are used medicinally as an antiseptic and expectorant. Under no circumstances should coal tar creosote be taken internally. Although creosote bush does not grow in the chaparral plant community, the dried leaves of this shrub are the source of "chaparral tea," a controversial herbal remedy with antitumor properties. The leaves contain a powerful antioxidant that apparently destroys tumor cells; however, there are reported cases of liver toxicity, including toxic hepatitis and jaundice.
Some resins are referred to as gums, but they are chemically very different. True gums are complex polysaccharides composed of many sugar subunits. Although the sap of the mastic tree (P. lentiscus) is called a gum, it is really an oleoresin used in perfumes, chewing gums, pharmaceuticals, dental adhesives, and in high grade varnishes for protecting pictures. Gum mastic is one of the oldest known high grade resins utilized by people, and it is extensively cultivated on the Greek island of Chios. Gum guaiac is another famous resin from a Caribbean tree called lignum vitae (Guaiacum officinale), one of the world's hardest and heaviest woods. A similar species (G. sanctum) is native to the Florida Keys. Both species are members of the caltrop family (Zygophyllaceae) along with North and South American creosote bush and the ubiquitous puncture vine (Tribulus terrestris). The name lignum vitae means "wood of life," owing to the medicinal properties of the heavy, resinous wood. During the days of masted sailing ships, the wood and sweet-smelling resin globs were sought after for treatments and cures for a variety of human ailments, including gout, syphilis and rheumatism. Today the resin is still used for expectorants and as a dye to detect the presence of occult (hidden) blood. Peroxidase enzymes in the blood cells oxidize chemicals in the resin resulting in a characteristic blue-green color change. The raw resin contains about 15 percent vanillin (artificial vanilla), resulting in the sweet aroma. The density and high resin content of the wood make it extremely resistant to friction and abrasion and account for its remarkable self-lubrication properties. In fact, under certain conditions the wood wears better than iron. Because of this, the wood has been highly valued for pulley sheaves, bearings, casters, food-handling machinery, and especially for end grain thrust blocks which once lined the propeller shafts of steamships. During World War I, attempts were made to use other ironwoods such as Tabebuia guayacan from Central America for propeller shaft bearings, but the wood lacked the oily resin of lignum vitae.
1. Turpentines: A large group of oleoresins from gymnospermous trees. Raw or crude turpentine is essentially the sticky sap or pitch from coniferous trees. In the U.S., raw turpentine is largely derived from southeastern pines, including longleaf pine (Pinus palustris) and slash pine (P. elliotti) grown in large plantations. Crude turpentine is distilled in order to separate the volatile essential oils called "spirits" from the nonvolatile diterpene residue called rosin. Spirits of turpentine are used in thinners and other organic solvents, while rosin is used in the manufacture of varnishes and oil base paints (and for violin bows and baseball pitchers). Oil base paints also contain unsaturated drying oils, such as castor, tung and linseed oils. The settlement of North America was partially due to England's desire to rid herself of dependence on Scandinavian sources of resin, since the pitch was used to caulk ships and waterproof the rigging.
According to N.T. Mirov (The Genus Pinus, Ronald Press, 1967), all species of pines, except two California species, contain terpenes in their turpentines. The exceptional species are P. jeffreyi and P. sabiniana. The turpentines of these latter two species consists almost entirely of an alkane, n-heptane, with a small mixture of fragrant aliphatic aldehydes. The aldehydes produce distinctive odors in bark fissures of jeffrey pine variously described as resembling vanilla extract, butterscotch or pineapple. Pure heptane, distilled from the resin of P. jeffreyi, was used to develop the octane scale for rating petroleum as a motor vehicle fuel. The following account comes from Conifers of California by Ronald M. Lanner (1999): During the Civil War, Union manufacturers of turpentine used pitch from ponderosa pine (P. pondersosa) because southern pine resins (incl. longleaf and slash pines) were not available in the Confederate States. Sometimes pitch from Jeffrey pine containing volatile n-heptane would get into the heated vats and cause an explosion.
C7H16 (n-heptane)
2. Copals & Balsams A group of resins that form particularly hard varnishes and fragrant perfumes. They are derived from tropical trees in the legume family (Fabaceae), including West Indian locust (Hymenaea courbaril(the source of Central American copal varnish & incense), and the closely related East African copal (H. verrucosum. Copal resins also come from the Kauri pine Agathis australis, an important New Zealand source of varnishes, and the closely related amboyna pine (A. alba), another source of copal resins from the East Indies and Malaysia. In Chiapas, Mexico, Dominican Republic, and parts of Colombia and Brazil, the subterranean resin globs of ancient Hymenaea trees (related to the present day West Indian locust) have transformed into amber through a remarkable chemical process requiring millions of years. During the polymerization process, the volatile terpenes escape and the nonvolatile terpenes bond together forming a hard plastic-like polymer that is resistant to natural decay processes and the ravages of time. Unlike copal resins and balsams, the amber is unaltered by organic solvents such as alcohol, acetone and ether. Although some copals will take a high polish, they contain volatile terpenes that gradually evaporate, causing the surface to become deeply crazed like the cracked mud of a dry lake bed
Balsams are oleoresins containing volatile essential oils and nonvolatile resins. Because of the volatile, strongly-scented terpene component, balsams are used in perfumes, incenses and medicines. The well-known "Canada balsam" is a natural turpentine collected from resin blisters on the bark of Abies balsamea, a cone-bearing tree of the northern United States and Canada. Central and South American copaiba balsams (balsamos de copaiba) come from rain forest trees in the legume family, including Prioria copaifera, Copaifera reticulata and C. officinalis. The fragrant balsum-of-peru (Myroxylon balsamum) is gathered in Central America (El Salvador) by "balsameros," and used in medicines, soaps and perfumes.
3. Dammar Resins: East Indian and southeast Asian resins similar to copals. Like copals they are shiny and transparent when dry and are used extensively in the paint and varnish industry. They are primarily obtained from large rain forest trees of the dipterocarpus family (Dipterocarpaceae). Some of the sources for dammar resins in this family are Dipterocarpus turbinatus (also called gurjun balsam), and several species of Shorea, including S. aptera, S. hypochra, S. robusta and S. wiesneri.
4. Incenses: Fragrant, strong-scented oleoresins mostly from the torchwood family (Burseraceae) and the legume family (Fabaceae), including some of the copals and balsams discussed in the previous section. But probably the most famous incense resins come from the Burseraceae, including frankincense (Boswellia carteri) and myrrh (Commiphora abyssinica), native trees (or large shrubs) of the Middle East deserts. Some of the New World counterparts of this fascinating resinous family include Guatemalan incense (Protium copal) and gumbo limbo (Bursera simaruba), two incense species widely used by the Maya. Several closely related Mexican incense trees of the Sonoran Desert are called elephant trees because of their thick trunks resembling the legs of elephants, including B. odorata and B. microphylla. In fact, the latter species is native to remote, rocky canyons in the Anza-Borrego Desert of San Diego County. Another very resinous elephant tree in Baja California (Pachycormus discolor) belongs to the sumac family (Anacardiaceae).
5. Natural Lacquer: An oleoresin produced in resin canals of the Japanese lacquer tree Toxicodendron vernicifluum, a member the sumac family (Anacardiaceae). Related species, including poison oak (T. diversilobum), poison ivy (T. radicans) and poison sumac (T. vernix) also have a resinous sap that oxidizes and polymerizes into a dark, shiny lacquer. The resin canals also contain urushiol, the insidious allergen that gives these species their bad reputation. The name is derived from "urushi", Japanese name for lacquer made from the sap of the Japanese lacquer tree ("kiurushi" or "urushi ki"). Urushiol is a phenolic compound that causes serious dermatitis in hypersensitive people. It is discussed in the Wayne's Word poison oak article (see link at end of this paragraph). Shellac is prepared from a resinous excretion on the twigs of several species of Asian and southeast Asian trees by the lac insect. The lac insect belongs to the Order Homoptera (along with aphids, scale insects and mealy bugs), and depending on the reference, it is listed as Tachardia lacca or Laccifer lacca.
6. Amber: A hard, terpene material that develops from subterranean globs of resin. During the polymerization process (which may take millions of years), the volatile terpenes escape and the nonvolatile terpenes bond together forming a hard plastic-like polymer that is resistant to natural decay processes and the ravages of time. Unlike copal resins and balsams, the amber is unaltered by organic solvents such as alcohol, acetone and ether. Since the first records of neolithic man in Europe, approximately 5,000 years ago, amber has been cherished for its natural beauty and mysterious properties. Amber trade routes of the Phoenicians, Greeks and Romans crossed Europe from the Baltic Sea region, where it was found in great abundance. For decades Baltic amber has been arbitrarily assigned to an extinct pine (Pinus succinifera) because of the presence of succinic acid; however, IR (infrared spectroscopy) studies show that Baltic amber may be more closely related to resins of broad-leafed conifers of the araucaria family (Araucariaceae). According to J.H. Langenhein (Plant Resins: Chemistry, Evolution, Ecology, and Ethnobotany, 2003), Baltic amber contains pinaceous inclusions (wood fragments and cones) but with araucarian chemical characteristics, so the origin of these vast deposits remains an enigma. Today the only evidence of araucariads in the northern hemisphere comes from amber deposits and petrified wood, such as occurs at Petrified Forest National Park in Arizona. In New Zealand a living araucariad forest of "kauri pine" Agathis australisproduces copious amounts of resin that once formed a thriving industry for hard, durable varnishes and linoleum. Large lumps of hardened resin (up to 100 pounds in size) were dug out of the ground in extensive forested areas of North Island. Forests such as this may have once flourished in the Baltic region 60 million years ago.
Throughout the world, the most copious resin-producing trees occur in tropical regions. These complex mixtures of terpene resins may serve as a chemical defense against the high diversity of plant-eating insects and parasitic fungi found in the tropics. Many tree species are known to produce amber, but most neotropical (New World) amber comes from the fossilized resin of extinct Hymenaea protera, an ancient leguminous tree that once grew throughout the Caribbean region, Mexico, Central and South America more than 30 million years ago (see: D.A. Grimaldi, Amber: Window to the Past, 1996). The tropical distribution and chemistry of this beautiful honey-colored amber correlates remarkably well with the present-day West Indian locust (Hymenaea courbaril). Unlike the extinct progenitors of Baltic amber, the West Indian locust is the living descendent of most neotropical amber. And unlike most trees of the New World tropics, the genus Hymenaea allows one to peer into the geologic past--to actually see some of the creatures it was associated with millions of years ago, perfectly preserved in a transparent tomb of fossilized resin.
| A termite embedded in a transparent tomb of fossilized resin known as amber. The piece was sold as Baltic amber, but it probably has a tropical New World origin. The slender, beadlike (moniliform) antennae are quite different from those of ants. Ant antennae are elbowed with a distinct right angle bend. Both insect orders are common in New World amber dating back 25 million years. |
7. Phenolic Resins Of Cannabis: The pure resin of marijuana (Cannabis sativa) is called hashish. It contains a mixture of volatile mono and sesquiterpenes, along with about 30 phenolic cannabinoids. The most potent cannabinoid is delta-tetrahydrocannabinol (THC), the psychoactive ingredient of marijuana. Globs of resin are produced at the tips of glandular hairs (trichomes) on the inflorescences and floral bracts of female plants. The male plants generally lack the dense glandular hairs and are used for their strong and very durable stem fibers called Indian hemp.
| Left: Close-up view of the inflorescence of a female marijuana plant (Cannabis sativa). The threadlike structures are styles of pistillate (female) flowers. The granular appearance is due to numerous glandular hairs (trichomes), each with a blob of resin. Male plants generally lack the dense, glandular hairs. Right: Microscopic view of the inflorescence showing numerous gland-tipped hairs called trichomes, each with a tiny blob of resin at the tip. The resin contains a mixture of volatile mono and sesquiterpenes, along with several phenolic cannabinoids. The most potent psychoactive cannabinoid is delta-tetrahydrocannabinol (THC). |
An Excellent Reference About Plant Resins
Langenheim, J.H. 2003. Plant Resins (Chemistry, Evolution, Ecology and Ethnobotany). Timber Press, Portland Oregon. |
|
C. Polyterpenes: Elastic terpenes composed of thousands of C5H8 isoprene subunits. They are found in the milky latex sap produced inside special cells called laticifers or laticiferous tubules in the secondary phloem. Laticifers are single cells or strings of cells that form tubes, canals or networks in various plant organs. Plant families which produce copious amounts of milky latex include the euphorbia family (Euphorbiaceae), milkweed family (Asclepiadaceae), mulberry family (Moraceae), and the dogbane family (Apocynaceae). The main source of natural rubber comes from Hevea brasiliensis (Euphorbiaceae), a rain forest tree native to the Amazon Basin. Ninety percent of all natural rubber comes from the latex sap of this species. A process called vulcanization (discovered by Charles Goodyear) produces cross-linkages between the thousands of isoprene subunits in the rubber latex, improving the elasticity and durability of the rubber. Although synthetic butadiene and styrene polymers are commonly used in the manufacture of tires, natural rubber is still incorporated into radial and high impact airplane tires to provide more resilience. Other rubber-producing plants include Ficus elastica (Moraceae) and gutta-percha (Palaquium gutta, Sapotaceae). Because the latex of gutta percha contains fewer branched polyterpene chains than Hevea rubber, it is not as elastic. A native shrub of Mexico and the southwestern United States called guayule (Parthenium argentatum, Asteraceae) contains a latex sap with polyterpenes similar to those found in Hevea rubber. It is a potentially good source of natural rubber, possibly grown on large plantations in arid desert regions.Chicle is a polyterpene from the naseberry or sapodilla tree (Manilkara zapota), a native tree of Central America and the West Indies. Chicle is extracted from the sap of the trunk and is used in some chewing gums. Large trees were originally tapped by tree-climbing workers called chicleros. Although the rubbery latex is a polyterpene, it does not vulcanize into durable rubber. Although natural chicle is still used, most of today's chewing gums are made from a synthetic vinyl gum base. The fruit of the chicle tree is also known as the sapodilla. The fleshy pulp is used to make sapodilla custard and ice cream.
D. Other Terpenes: This group includes many additional terpene derivatives produced in a variety of diverse plant families. Since some of these are soluble in nonpolar solvents such as alcohol, they are often placed in the lipid category. Many of these terpenes occur naturally as glycosides with attached sugar molecules. Diterpenes include gibberellins, plant hormones controlling stem (internode) elongation, fruit development and seed germination. Triterpenes include saponins that foam in water and sterols (steroids) from which animal sex hormones are derived. [See steroids under the lipid category above, but use the terpene category for steroids on Botany 115 Exam #2.] Carotenoids are tetraterpenes composed of 8 isoprene subunits. Beta-carotene (C40H56) is the precursor of the anti-oxidant vitamin A (C20H28O), also called retinol.
Carotenoids are water insoluble plastid pigments associated with chlorophylls in chloroplasts and in colored plastids called chromoplasts. They are found in tomatoes, red peppers, carrots, sweet potatoes, and in many colorful flowers and autumn leaves. [Note: Some of the brilliant red pigments in autumn leaves are actually anthocyanins, a different class of chemicals called phenolic compounds.] The bright red pigments in snow algae, and in halophilic algae and bacteria, are carotenoids. In these unicellular organisms the pigments help to protect the delicate cells from intense UV light from the sun. The bright red pigment in the exoskeletons of lobsters, crayfish and crabs is carotenalbumin, including fat-soluble carotenoid pigment called astaxanthin conjugated with protein. The bright red color shows up when the lobster in boiled in water because the pigment separates from the protein. Other carotenoids are found in insect wings, brightly-colored corals, and in the skins of fish, amphibians and marine invertebrates. Egg yolks contain astaxanthin which produces the characteristic yellow color. In fact, chickens throughout the world are fed astaxanthin in their diets to intensify the yolk color. One important source of astaxanthin for chicken feed are the petals of red marigolds (Tagetes). In fact, fields of bright red marigolds are grown for this purpose in coastal valleys of central California. The petals are so rich in xanthophylls that the reddish pigment readily rubs off on your fingers. Since flamingos cannot synthesize carotenoid pigments, their pink plumage in the wild results from a diet rich in shrimp and other crustaceans. In captivity, they also fed supplemental astaxanthin in their diet to intensify their pink color.
| Petals (ray corollas) from bright red hybrid marigolds (Tagetes) are an important source of xanthophyll pigments, such as astaxanthin. They are grown for seed in the coastal valleys of Central California. |
Other carotenoids include zeaxanthin, a xanthophyll pigment responsible for the yellow color of corn kernels (Zea mays). Another carotenoid pigment comes from achiote or annatto (Bixa orellana), a large shrub native to tropical America. The outer covering of achiote seeds contains bixin, a bright red dye that was used to dye clothing during ancient times. Today it is sold as a paste for food coloring in Latin American countries. It is also used as body paint by native South American people.
Ripe tomatoes are particularly rich in the carotenoid lycopene (C40H56). In addition to imparting the bright red color to tomatoes, 40 milligrams of lycopene ingested daily may reduce the risk of atherosclerosis (clogged arteries) and heart disease. Lycopene may also reduce the risk of certain cancers, including cancers of the prostate, lung, bladder, cervix, skin and digestive tract. According to Dr. A.V. Rao (Experimental Biology and Medicine 227 (10): 908-913, 2002), lycopene is an antioxidant that prevents the oxidation of low density lipoproteins (LDLs). High LDL oxidation is associated with increased risk of atherosclerosis and coronary heart disease. According to the Merck Index (1983), one kilogram (2.2 pounds) of fresh tomatoes yields 20 milligrams of lycopene. To obtain 40 milligrams of lycopene, you would need to eat about eight medium-sized tomatoes (or four large tomatoes) every day. Apparently lycopene is absorbed more readily in the processed form, such as tomato paste and juices. Several on-line references recommended drinking two glasses of tomato juice every day. Perhaps it is also wise to eat plenty of tomato soup, stewed tomatoes and tomato sauce on pasta and pizzas.
Intact pollen grains have been extracted from sedimentary strata that is millions of years old, and from animal exrement that has passed through a digestive system. The perfectly preserved pollen grains still retain the distinctive grooves and ornamentation in the outer exine layer. The chemical composition of exine is different from the siliceous shells of microscopic diatoms and grass phytoliths found in fossilized dinosaur dung. It also different from the chitinous exoskeletons of arthropods and the calcareous shells of mollusks. The exine layer is composed of a tough biopolymer called sporopollenin. Although it contains only carbon, hydrogen and oxygen, it is different from carbohydrate polymers such as starch and cellulose. In fact, it is one of the most stable organic compounds known. It has been extracted from plant spores using strong acid and alkali solutions that would disintegrate other substances. Although its structure is not completely understood, some scientists describe sporopollenin as "polycarotenoid in character." |