The genus Allium comprises more than 600 different species, which are found throughout North. America, Europe, North Africa, and Asia. Approximately 30 species have been regularly used for edible purposes (although less than half of these are subject to cultivation), with the most important being onions, garlic, leeks, chives, and shallots.
In terms of their common botanical characteristics, alliums are mainly herbaceous plants, incorporating various underground storage structures made up of rhizomes, roots, and bulbs. The foliar leaves alternate, often sheathing at the base to give the superficial impression that they originate from an aboveground stem. As a rule, the flower cluster, or inflorescence, is umbrella-like, with all the flower stalks radiating from the same point (umbel); the flowers are pollinated by insects; the fruits take the form of a capsule or berry; and the seeds are numerous and endospormic.
This genus is placed in the lily family. Most, but not all, of the species possess the pungent odor typical of onion and garlic. In addition to alliums, species of Ipheion, Adenocalymma, Androstephium, Esperocal-lis, Talbaghia, Nectarosiordum, Nilula, and, possibly, Descurainia produce pungent odors (Fenwick and Hanley 1985a).
Onions
History
Antiquity. The onion (Allium cepa) may have originated in Persia (Iran) and Beluchistan (eastern Iran and southwestern Pakistan). But it is also possible that onions were indigenous from Palestine to India. They have been known and cultivated for many thousands of years and no longer grow wild. Their range - virtually worldwide - now includes China, Japan, Europe, northern and southern Africa, and the Americas (Hedrick 1972).
The consumption of onions is depicted in the decoration of Egyptian tombs dating from the Early Dynasty Period, c. 2925-c. 2575 B. C. During the Old Kingdom, c. 2575-c. 2130 B. C., onions were used as religious offerings. They were put on altars and, as is known from mummified remains, were employed in preparing the dead for burial (placed about the thorax and eyes, flattened against the ears, and placed along the legs and feet and near the pelves). Flowering onions have often been found in mummies’ chest cavities (Jones and Mann 1963). If Juvenal (Roman poet and satirist, c. A.D. 55-127) is to be believed, a particularly delicious onion was worshiped as a god by certain groups in ancient Egypt (Hyams 1971).
The Greek historian Herodotus reported that onions, along with radishes and garlic, were a part of the staple diet of the laborers who built the Great Pyramid at Giza (2700-2200 B. C.) (Jones and Mann 1963). Egyptian onions were said to be mild and of an excellent flavor, and people of all classes (save for priests, who were prohibited from eating them) consumed them both raw and cooked (Hedrick 1972).
In Sumeria (southern Iraq), onions were grown and widely used for cooking 4,000 years ago (Fenwick and Hanley 1985a), and both garlic and onions have been unearthed at the royal palace at Knossos in Crete (Warren 1970). Minoan voyages from the eastern Mediterranean (2000-1400 B. C.) doubtless helped in dispersing alliums from that region.
The ancient Greek physician Hippocrates (460-375 B. C.) wrote that onions were commonly eaten, and Theophrastus (c. 372-287 B. C.) listed a number of onion varieties, all named after places where they were grown: Sardian (from western Turkey), Cnidian (from southern Turkey), Samothra-cian (from a Greek island in the northeast Aegean), and Setanian (possibly from Sezze or Setia in central Italy) (Jones and Mann 1963;Warren 1970).
Asia. According to Charaka, a Hindu physician of the second century A. D., the onion (as in ancient Egypt) was thought not to be a suitable food for persons pursuing the spiritual life. Thus, the onion was taboo for orthodox Brahmins, Hindu widows, Buddhists, and Jains (Hyams 1971).
In China, the fifth-century treatise on agriculture, Ch’i-min-yao-shu (Essential Arts for the People) by
Chia Ssu-hsieh, described the cultivation of ts’ung, or spring onion (Allium fistulosum L.), along the Red River valley (Li 1969). Infusions of onion have long been used in China as a treatment for dysentery, headache, and fever (Hanley and Fenwick 1985).
In 1886, Kizo Tamari, a Japanese government official, stated that in his country, onions did not have globular bulbs but were grown like celery and had long, white, slender stalks (Hedrick 1972). Interestingly, some modern Japanese communities forbid the cultivation, but not the consumption, of the spring onion (Kuroda 1977).
Europe. Columella (Lucius Junius Moderatus Columella), a Spanish-born Roman agriculturalist of the first century A. D., wrote of the Marsicam, which the country people called unionem (a term that may be the origin of the English word “onion” and the French oignon) (Fenwick and Hanley 1985a). Columella’s contemporary, the Roman gourmet Apicius (Marcus Gavius Apicius), created several recipes that employed onions, although he viewed the vegetable as a seasoning rather than a food in its own right (Fenwick and Hanley 1985a).
Writing at about the same time as Apicius, Dioscorides (a Greek military physician) described onions as long or round and yellow or white, and provided detailed discussions of the uses of garlic, onion, and other alliums as medicinal plants (Jones and Mann 1963;Warren 1970).
Still another contemporary, Pliny the Elder, told his readers that the round onion was the best and that red onions were more highly flavored than white. His Natural History described six types of onions known to the Greeks: Sardian, Samothracian, Alsidenian, Setanian, the split onion, and the Ascalon onion (shallot). Pliny claimed onions to be effective against 28 different diseases (Fenwick and Hanley 1985a).Then, later on in the first millennium, Palladius (Rutilius Taurus Aemilianus Palladius), a Roman agriculturist in about the fourth century (or later), gave minute directions for culturing onions and comprehensively described their cultivation (Hedrick 1972).
By the beginning of the second millennium, many accounts of foodstuffs were being penned by monks. For example, Peter Damian (1007-72), the founder of a reformed congregation of Benedictines in central Italy, indicated that he permitted a moderate dish of edible roots, vegetables - mostly onions, leeks, and chickpeas - and fruit on days when fasting was not prescribed. These meals were eaten both cooked and uncooked, and sometimes enlivened with oil on special feast days (Lohmer 1988).
The German Dominican monk and scientist Alber-tus Magnus (1193-1280) did not include onions in his lists of garden plants, but garlic and leeks were represented there, suggesting the esteem in which they were held. Onions, however, were exotic plants understood to have favorable effects on fertility by
Generating sperm in men and lactation in women (Mauron 1986).
By the sixteenth century, onions were no longer exotic. The Portuguese physician. Amatus Lusitanus (1511-68) wrote that they were the commonest of vegetables, occurring in red and white varieties, and had sweet, strong, and intermediate qualities. The German physician and poet Petrus Laurembergius (1585-1639) described some of these qualities, writing of the Spanish onion as oblong, white, large, and excelling all others in sweetness and size; he further reported that at Rome, the Caieta variety brought the highest price, but at. Amsterdam the most valued variety was the St. Omer.
A nutritional revolution occurred in the nineteenth century, when food items previously monopolized by the upper classes became available to all. The defeat of scurvy began with the addition to the diet of potatoes and onions, which were progressively supplemented with other legumes and fruits. By the middle of the nineteenth century, deaths from tuberculosis were in decline. Among other things, this was the product of the continuing introduction into the diet of foods containing vitamins A, C, and E, as well as meat and fish, which provide the amino acids vital to the creation of antibodies (Knapp 1989).
The Americas. It is probable that the men of Christopher Columbus’s crews sowed onions on Hispaniola as early as 1494, and Hernando Cortes reportedly encountered onions, leeks, and garlic on his march to Tenochtitlan in 1519. Interestingly, native Mexicans apparently had a lengthy acquaintance with this Eurasian plant, because it had a name - xonacatl (Hedrick 1972).
Onions were mentioned as cultivated in Massachusetts as early as 1629, in Virginia in 1648, and at Mobile, Alabama, in 1775. By 1806, six varieties of onions were listed as esculents in. American gardens. In 1828, the potato onion (multiplier onion) was described as a vegetable of late introduction into the United States, and by 1863, 14 varieties were mentioned (Hedrick 1972;Toma and Curry 1980).
Recent production statistics. The major producers of dry onions (cured but not dehydrated) in 1996 were (in metric tons) China (9,629,895), India
(4.300.000) , the United States (2,783,650), Turkey
(1.900.000) , Japan (1,262,000), Iran (1,199,623), Pakistan (1,097,600), and Spain (1,018,100), and total world production was 37,456,390 metric tons. The major producers of spring onions (scallions) were Mexico (702,478), Korea (553,000), Japan (545,600), China (282,329), Turkey (230,000), and Nigeria (200,000), and world production was 3,540,595 metric tons.
The major exporters of onions in 1996 were the Netherlands, India, the United States, Argentina, Spain, Mexico, Turkey, and New Zealand. Major importers were Germany, the Russian Federation, Brazil, Malaysia, Saudi. Arabia, and the United. Arab Emirates.
Horticulture and Botany
Botany. The common onion is known only in cultivation. Propagation is usually by division, although some strains may also produce seed. Spring onions, used mainly in salads, are always grown from seed and harvested young. Pickling onions are made small by planting them close together (Traub 1968).
Onion leaves are the thickened bases of the normal leaves from the previous season. The bulb is composed of fleshy, enlarged leaf bases; the outermost leaf bases do not swell but become thin, dry, and discolored, forming a covering (Fenwick and Hanley 1985a). The onion usually flowers in the spring. Honeybees prefer the nectar of A. cepa to that of A. fistu-losum (green onions) (Kumar and Gupta 1993).
Cultivation. Two crops of onions are grown each year in the United States. That of the spring is grown in. Arizona, California, and Texas. The summer crop, much larger, consists of nonstorage produce, mostly from New Mexico, Texas, and Washington, and storage produce, grown mainly in Colorado, Idaho, Michigan, New York, Oregon, and Washington (Fenwick and Hanley 1985a).
Onions grow best in fine, stone-free, well-irrigated soils. Their comparatively thick, shallow roots require high levels of nitrogen, phosphorous, and potassium for maximum yield. The onion does not compensate for water stress and is sensitive to salinity. Flavor maturation and bulb development are affected by high temperature, high light intensity, soil moisture, and nitrogen deficiency (Brewster 1977a, 1977b). Increased flavor strength is associated with higher levels of applied sulfate (Platenius 1941; Kumar and Sahay 1954). Bulb formation depends upon increased daylength, but the daylength period required varies greatly between cultivars (Austin 1972).
Intercropping and rotation. Onions are the highest-yielding and most profitable inter - or border-crop for finger millet (Eleusine coracana) wherever it is grown (Siddeswaran and Ramaswami 1987). With tomatoes, planting four rows of onions (15 centimeters apart) between two rows of tomatoes has provided a 36 percent higher tomato equivalent yield without significantly affecting the number, average weight, and marketable yield of the tomato fruits. The tomato and onion combination also provides the highest net returns and maximum profit (Singh 1991).
Harvesting. Mature onions suffer lower storage losses than those harvested early. As onions reach maturity, the tops soften just above the bulb junction and cause the leaves to fall over. They are usually harvested when most of the plants are in this state (Kepka and Sypien 1971; Rickard and Wickens 1977). Harvesting methods depend on the size of the crop, the climate, and regional or national practices (Jones and Mann 1963).
After harvesting, unless the crop is immediately sent to market, curing is necessary. The purpose of curing is to dry the skins and the top of the onion, forming an effective barrier against attack by microorganisms and, at the same time, minimizing the weight loss of the bulb. The onion is cured when the neck is tight, the outer scales are dry, and 3 to 5 percent of the original bulb weight is lost (Thompson, Booth, and Proctor 1972).
Curing can be natural or artificial. Windrowing, the traditional method in Britain, leaves the onions in the field, with the leaves of one row protecting the bulbs in the next. Direct exposure of the bulbs to the sun, especially under moist conditions, may lead to fungal damage (Thamizharasi and Narasimham 1993). In many countries, the onions are braided into bunches and hung up to dry (Thompson 1982).
Artificial curing techniques include forced heated air, vacuum cooling, cold storage, and infrared irradiation (Buffington et al. 1981). A small-capacity dryer has been developed in India (Singh 1994).
Storage. In addition to effective harvesting and curing, the critical factors for successful storage are culti-var type, storage conditions, and storage design. Losses from rotting and sprouting are more important than those from desiccation. Onions best suited for long-term storage (up to six months) usually have high amounts of dry matter and soluble solids, a long photoperiod during bulb maturation, and strong pungency. Red onions store better than white ones (Jones and Mann 1963;Thompson et al. 1972).
Temperature and relative humidity are the most important factors in storage conditions. Cold storage produces the best results but is not feasible in the tropics, where high-temperature storage may be effective, because dormancy is longer at 0° C and at 30° C than in between (10-15° C). Humidity should be about 70 to 75 percent (Robinson, Browne, and Burton 1975). Controlled-atmosphere storage losses depends on the quality and condition of the crop prior to storage (Adamicki and Kepka 1974).
In storage design, aeration is important for curing the onions and ventilating the heap. Consequently, slatted floors (or a similar layout, so that air can move through the bulbs from below) are employed. The onions are positioned so that air flows throughout the heap; otherwise, the moist, warm air retained in the middle leads to sprouting or rotting. The heaps should not be more than 8 feet high, and - especially where temperature, aeration, and humidity control are difficult - shallow heaps are recommended (Hall 1980).
Gamma irradiation is an effective inhibitor of sprouting in onion and garlic bulbs. Studies have shown that eating irradiated onions does not harmfully affect animals or their offspring, but irradiation can cause discoloration, may not affect rotting, and may make onions more susceptible to aflatoxin production (Van Petten, Hilliard, and Oliver 1966; Van Pet-ten, Oliver, and Hilliard 1966; Priyadarshini and Tulpule 1976; Curzio and Croci 1983).
Pathogens and Pests
Fungi
DOWNY MILDEW. Downy mildew (Peronospora destructor [Berk.] Casp.) was first reported in England in 1841. It is now widespread and particularly prevalent in cool, moist climates such as the coastal regions bordering the North Sea in Britain and those of the northwestern (Washington, Oregon, and California) and northeastern (New York and New England) United States. This fungus attacks onions, garlic, leeks, and chives alike. Early infection may kill young plants, and survivors can be dwarfed, pale, and distorted. Later infection causes chlorosis and yellowing of the leaves and stems. Some plants may be systemically infected and, if used for propagation, can serve as sources of inoculum in the seed crop.
When infected, the bulb tissue tends to soften and shrivel, and the outer fleshy scales become amber-colored, watery, and wrinkled. Underlying scales may appear healthy and yet be heavily infected. The fungus commonly overwinters in young autumn-sown onions whose leaves have been infected by neighboring summer crops.
Downy mildew can be controlled by growing onions on uncontaminated land without adjacent diseased crops. Good-quality, noninfected onions should be used, and planting should be done on open, well-drained land (Fenwick and Hanley 1985a).
WHITE ROT. White rot (Sclerotium cepivorum Berk.) was first noted in mid-nineteenth-century England and, like downy mildew, infects all the alliums under scrutiny in this chapter. The fungal attack is favored by dry soil and cool conditions. It develops rapidly between 10° C and 20° C and is inhibited above 24° C, although periods of dry weather can lead to devastating attacks in the field. When young plants are attacked, the disease spreads rapidly. External signs are yellowing and necrosis of leaf tips. Roots and bulbs are also affected. The bulb scales become spongy, are covered with fluffy white mycelium, and develop black sclerotia. The fungus appears to overwinter as sclerotia, and, in fact, the sclerotia may survive 8 to 10 years or more in the absence of host plants. Growing seedlings and sets for transplanting in noninfected soil, and the use of long rotations, are of some benefit in controlling this fungus. Chemical treatment with mercuric chloride, lime, and 2,6-dichloro-4-nitroaniline have also proven effective (Fenwick and Hanley 1985a).
ONION SMUDGE. Common now in Europe and the United States, onion smudge (Collectotrichum circi-nans [Berk.] Vogl.) was first reported in England in 1851. It affects mainly white varieties of onion but has been reported in shallots and leeks. It is confined to the necks and scales, where it causes blemishes, reducing the market value of the crop. Rarely attacking the active growing parts of the plant, it is confined on colored onions to unpigmented areas on the outer scales of the neck. Onion smudge requires warm, moist conditions (10° C to 32° C, optimum 26° C). Conidia, or fungal spores, are produced abundantly and are scattered by spattering rain. With suitable conditions, a conidial spore will germinate within a few hours. Pungent onions resist smudge better than mild ones. Crop rotation, good husbandry, and carbamate sprays can minimize the damage. Drying the onions in hot air may be necessary, and curing under dry, well-ventilated conditions is important (Fenwick and Hanley 1985a).
ONION SMUT. Probably originating in the United States in the late nineteenth century and first reported in Britain in 1918, onion smut (Urocystis cepulae Frost) attacks bulb and salad onions as well as leeks, shallots, chives, and garlic. Infection occurs from two to three weeks after sowing, and a high percentage of the infected plants subsequently die. Elongated, leaden streaks discolor the scales and the growing leaves, which can also become thickened and malformed. The streaks develop into smut sori, which rupture and release spores that can survive up to 20 years in soil. Measures to control this fungus include avoiding infected areas, pelleting seed with hexachloroben-zene, dusting with thiram or ferbane, and applying fungicides (Fenwick and Hanley 1985a).
NECK ROT. Caused by three different species of Botry-tis, neck rot is probably the most widely distributed and most destructive disease of onions in storage. It was first reported in Germany (1876) and then in the United States (1890) and Britain (1894). Infection occurs in the field but is usually not noticed until harvesting occurs. The first signs are a softening of bulb scales and the development of sunken brown lesions; a definite border between fresh and diseased tissue can be seen. The bulb desiccates and collapses. If the onions are stored in moist conditions, a secondary spread may take place. Infection occurs primarily from spores dispersed by wind or water before, during, or after harvest. White onions seem more susceptible than yellow or colored varieties, and pungent onions are less affected than mild-flavored varieties. Practical controls are thin sowing, careful handling during harvest, and providing optimal storage conditions. Zineb and other chemicals, including carbamate sprays, reduce infection, and in recent years, benomyl seed dressings have also been used effectively (Fenwick and Hanley 1985a).
Bacteria
SOFT ROT. The soft rot pathogen (Erwinia carotovora) enters onions through wounds that occur during harvest, transportation, and storage, or in the necks of uncured or slow-curing varieties. The infection usually starts at the bulb neck, with external signs of sponginess and a foul-smelling exudate from the neck when the bulb is squeezed. Soft rot occurs most commonly in humid weather and is transported by the onion maggot, which is itself contaminated by the rotting vegetation it consumes and, consequently, lays eggs carrying the bacteria. Control involves avoiding damage to the bulbs during and after harvest, drying them thoroughly and rapidly, using the lowest practicable storing temperature, and eliminating all damaged bulbs (Fenwick and Hanley 1985a; Wright, Hale, and Fullerton 1993). Also important is moving bulbs under cover and drying them if wet weather is expected during field-curing (Wright 1993).
Viruses. “Aster yellows,” spread by the six-spotted leafhopper (Macrosteles facifrons), is an important viral disease of onion as well as of carrot, barley, celery, endive, lettuce, parsley, potato, and salsify. Yellowing young leaves are followed by the appearance of yellowed shoots; and roots become small and twisted. Control measures consist of reducing or eradicating the leafhopper population where aster yellows is prevalent (Fenwick and Hanley 1985a).
Nematodes. The bulb and stem nematode (Dity-lenchus dipsaci [Kuhn] Filipjer) is widespread in the Mediterranean region but has also been found on onions and garlic in the United States, on onions in Brazil and England, and on onions and chives in Holland. It causes a condition known as “onion bloat.” Dead plant tissue can contain dormant nemas, which are probably an important source of infestation. Chloropicren/steam fumigation and other treatments have proven effective, but bromine-containing nema-tocides should be avoided. Both onion and garlic are bromine-sensitive and will not produce good crops for up to 12 months if bromine residues are present in the soil.
Ditylenchus dipsaci is widespread in southern Italy, where it reproduces on several wild and cultivated plant species. Among vegetables, the most severely damaged are onion and garlic, but broad bean, pea, and celery also suffer damage. In the Mediterranean area, the nematode mainly infects host plants from September to May, but reproduction is greatest in October, November, March, and April, when soil moisture, relative humidity, and temperatures are optimal. Symptoms of nematode attack are apparent in the field from late February to April and in nurseries during October and November. As a result, early crops are damaged more than late crops. Nematodes survive in the soil and in plant residues. However, seeds from infested plants, except those of broad bean and pea, have rarely been found to harbor nematodes. The use of seeds, bulbs, and seedlings free of nematodes is a prerequisite for successful crop production. Cropping systems, soil treatments with fumigant and nonvolatile nematocides, and soil solar-ization of infested fields are recommended for effective and economic nematode control (Greco 1993).
Insects. Although many insects can attack onions, the two major culprits are the onion thrip (Thrips tabaci Lind.) and the onion maggot, the larval stage in the development of the onion fly (Hylemya antiqua Meig.). The onion thrip punctures leaves and sucks the exuding sap, leaving whitish areas on the leaves. Infestation is worse in very dry seasons and can often lead to the destruction of entire crops. Effective chemicals are available to control this pest, and results have shown that a 40 percent bulb-yield reduction occurs on nontreated plots as compared with treated ones (Domiciano, Ota, and Tedardi 1993).
The onion maggot is a pest of considerable economic importance. Both the fly and its eggs are carriers of the soft rot pathogen E. carotovora Holland. The adult female lays 30 to 40 eggs in the soil around the onion plant or on the onion itself, especially where plants are damaged, decaying, or already infected with larvae. Good husbandry, the destruction of onion waste, and chemicals such as aphidan, EPBP, fensulfothion, fonofos, malathion, or phoxim are used to control the onion fly and its offspring (Fenwick and Hanley 1985a).
Processing
Dehydrated onion pieces. After grading and curing, onions are peeled using lye or the flame method, whereby the roots and outer shell are burnt off in an oven, and the charred remnants are removed by washing. Next, the onions are sliced by revolving knives and dried by hot air forced upward through holes in the conveyor belt. For good storage and acceptable flavor stability, residual moisture content is about 4 to 5 percent. Moisture content can be reduced to the desired level in one to two hours (Gummery 1977). The onion pieces may then be used as such or converted into granules and flakes (or powder). Dehydrated onion pieces are widely employed in the formulation of sausage and meat products, soups, and sauces (Hanson 1975;Pruthi 1980).
Onion powder Onion powder is used in cases where onion flavor is required but the appearance and texture of onions are not, as in dehydrated soups, relishes, and sauces. Onion powder is made by grinding dehydrated onion pieces or by spray-drying. For spraydrying, onions are washed free of debris, rinsed, and blended to a puree. Dextrose (30 to 40 percent by weight) is added, and the mixture spray-dried at temperatures below 68° C. It can be dried in four minutes at 65° C to 68° C. The treatment destroys all pathogenic bacteria while reducing the bacterial population, and the end product has excellent keeping properties (Gummery 1977).
Onion oil. Distillation of minced onions that have stood for some hours produces onion-essential oil. The oil is a brownish-amber liquid that contains a complex mixture of sulfur and other volatiles. The oil has 800 to 1,000 times the odor of a fresh onion, and its price may be 1,000 times more expensive as well. It is used for its solubility, lack of color, and strong aroma. However, onion oil cannot be standardized because its composition depends on the onion variety, ecological conditions, season, and processing (Heath 1981).
Onion juice. Onion juice is produced by expressing the bulbs, flash-heating the liquor obtained to a temperature of 140° C to 160° C, and immediately cooling it to 40° C. Next, the juice is carefully evaporated to approximately 72 to 75 percent dry matter to preserve it without chemical additives. The concentrated juice is pale brown in color and possesses a strong, fresh onion odor. Further evaporation to 82 to 85 percent solids darkens the product and gives it a cooked, toasted effect preferred by many. The sensory qualities are sometimes enhanced by returning the aromatic volatile condensate to the juice. The extract is often mixed with propylene glycol, lecithin, and glucose to yield an onion oleoresin that has a flavor 10 times that of onion powder and 100 times that of the original bulb (Heath 1981).
Onion salt. In the United States, onion salt is a mixture of dehydrated onion powder (18 to 20 percent), calcium stearate (an anticaking agent - 1 to 2 percent), and sodium chloride.
Pickled onions. Onions are pickled in a 10 percent salt solution and preserved in vinegar. Generally, silverskin or button onions are used because they give a translucent product with the desired firmness of texture. Lactic acid bacteria are the important fermentation organisms, and care must be taken to keep the solution at 10 percent salinity. Finally, the salt is leached from the onions with warm water, and the bulbs are placed in cold, spiced vinegar and stored in sealed glass jars (Fenwick and Hanley 1985a).
Nutrition
The nutritional content of onions varies by variety, ecological conditions, and climate. According to the Nutrition Data System of the University of Minnesota, 100 grams (g) (3 53 ounces or 0.44 cup) of onion provides 38 kilocalories of energy, 1.16 g of protein, 0.16 g fat, and 8.63 g of carbohydrate.
Using the standard of the Recommended Dietary Allowances (tenth edition) for a male between 18 and 25 years of age, approximately 100 g or one-half cup of fresh onion provides 10.7 percent of the Recommended Dietary. Allowance (RDA) of vitamin C and 9.5 percent of folacin. Onions are high in potassium (157 milligrams [mg]) and low in sodium (3 mg).They contain small amounts of calcium, copper, iron, magnesium, manganese, molybdenum, phosphorus, selenium, and zinc (Raj, Agrawal, and Patel 1980). Other trace elements in onion are germanium, chromium, and lithium. Onions have no vitamin A and only small amounts of alpha-tocopherol, delta-tocopherol, thiamine, riboflavin, niacin, pantothenic acid, and vitamin B6.
In addition, 100 g of onions contain only small amounts of three fatty acids: saturated palmitic acid (0.02 g), monounsaturated oleic acid (0.02 g), and polyunsaturated essential linoleic acid (0.06 g). They have 2.1 g of dietary fiber, no starch, and 89.68 g of water. Sucrose (1.3 g), glucose (2.4 g), and fructose (0.9 g) are present. All essential amino acids are present in onions. Arginine (0.16 g), which increases during maturation (Nilsson 1980), and glutamic acid (0.19 g) are the most abundant.
Chemistry
The color of red onions is due to cyanidin glycosides, anthocyanins that contain glucose molecules (Fuleki 1971).With yellow onions, quercetin, a flavonoid, and its glycosides are responsible for the color of the dry scales. The outer scales of onions have been used in Germany for dyeing Easter eggs and household fabrics (Perkin and Hummel 1896; Herrmann 1958).The flavonoid content is usually greatest in the outer leaves and may act as a protection against predators (Tissut 1974; Starke and Herrmann 1976a).
The phenolic compounds catechol and protocate-chuic acid are found in greater quantities in colored onions than in white onions. The presence of these compounds in the outer dried scales is a contributing factor to the greater resistance of these types to smudge and neck rot diseases and to fungi-causing wild and soft rots (Walker and Stahman 1955; Farkas and Kiraly 1962).
The most important nonstructural polysaccharide in onion is a group of fructose polymers called fruc-tans. Fructose commonly forms chains of 3 to 10 molecules, with chains of 3 and 4 molecules being the most common. It is thought that these polymers are used for storage carbohydrates and osmoregulation during bulb growth and expansion (Darbyshire and Henry 1978;Goodenough and Atkin 1981).
Onions contain pectins with high methoxyl content and of the rapid-setting kind. Pectin is used in the preparation of jellies and similar food products and is used by veterinarians as an antidiarrheal (Alexander and Sulebele 1973; Khodzhaeva and Kondratenko 1983). Onions also contain several sterols. Beta-sitosterol, cycloartenol, and lophenol are the most common, followed by campesterol. Beta-sitosterol is used as an antihyperlipoproteinemic (Oka, Kiriyama, and Yoshida 1974; Itoh et al. 1977).
Like garlic, onion has exhibited antioxidative activity, which can be increased by microwave heating or boiling. It has been shown that S-alkenyl cysteine sulfoxides are the most active components. Quercetin and other flavone aglycones also contribute to the total antioxidative capacities of onion and garlic extracts (Pratt and Watts 1964; Naito, Yamaguchi, and Yokoo 1981a, 1981b).
Onions produce thiamine propyldisulfide, which corresponds to the allithiamine formed in garlic from thiamine and allicin. Both compounds have been found effective against cyanide poisoning (Carson 1987).
Medicinal Use
Atherosclerotic. Onion is known to have a hypocho-lesterolemic effect, although not as strong as that of garlic (Bhushan et al. 1976). A study in China compared an onion-growing region to one without local onions. Both regions were similar in living standards, economic level, and dietary habits and customs. But people in the onion-growing region had a death rate from cardiovascular disease of 57 per 100,000 people, as compared with a cardiovascular-disease death rate in the other region of 167 per 100,000. The onion-growing region also had a significantly lower incidence of hypertension, retinal arteriosclerosis, hyperlipemia, and coronary artery disease (Sun et al. 1993).
Hypo - and hyperglycemic effects. A study has revealed that although a water extract of fresh or boiled onion did not affect fasting blood sugar in normal subjects, it did reduce the sugar levels in glucose-tolerance tests in a dose-dependent manner. From this result, it was suggested that onion has an antihyperglycemic effect instead of a hypoglycemic effect (Sharma et al. 1977).
The antihyperglycemic principle in onion has been tentatively identified as 2-propenyl propyl disulfide - a compound that has been found to lower the blood sugar and increase insulin levels but has not been observed to have any effect on free fatty-acid concentrations (Augusti 1974; Augusti and Benaim 1975).Another antihyperglycemic compound causing this effect is diphenylamine, found in onion and tea (Karawya et al. 1984).
Ill-effects of consumption. One problem with the consumption of onions is heartburn, but only among those predisposed to heartburn symptoms (Allen et al. 1990). Onions may also cause discomfort in people with ileostomies and children with Down’s syndrome (Bingham, Cummings, and McNeil 1982; Urquhart and Webb 1985).
As early as 1909, cattle deaths were attributed to eating sprouting or decaying onions (Goldsmith 1909; Fenwick and Hanley 1985c). Clinical signs of the condition may include onion odor in breath and urine, tainting of milk, diarrhea, staggering, and collapse. Provided that the illness has not reached an irreversible point, the symptoms (which develop with a week of onion feeding) may decline when the offending ingredient is removed from the diet. Treatment may also include injection of B-complex vitamins with penicillin-streptomycin (Gruhzit 1931; Farkas and Farkas 1974; Kirk and Bulgin 1979).
Garlic
History
Antiquity. Cultivated in the Middle and Far East for at least 5,000 years, garlic (Allium sativum) is believed to have originated from a wild ancestor in central Asia and is, possibly, native to western Tartary (Turkestan). At a very early period, garlic was carried throughout the whole of Asia (except Japan), North Africa, and Europe. In ancient China, Egypt, and India, garlic - like onions - was a highly prized foodstuff (Hedrick 1972; Hanley and Fenwick 1985).
In Egypt, the consumption of garlic is shown in tomb art dating from the Early Dynastic Period (c. 2925-2575 B. C.).The Codex Elsers, an Egyptian medical papyrus dating from around 1500 B. C., described 22 garlic preparations employed against a variety of complaints, including headache, bodily weakness, and throat disorders (Fenwick and Hanley 1985a).
The Bible (Num. 11:5) reports that after their Exodus from Egypt (about 1450 B. C.), the Israelites complained to Moses about the lack of garlic, among other things: “We remember the fish which we used to eat free in Egypt, the cucumbers and the melons and the leeks and the onions and the garlic.”
The Greeks, along with the Egyptians, regarded garlic as a defense against old age and illness, and athletes participating in the Olympic Games, (which began about 776 B. C.), regularly chewed it to improve stamina (Hanley and Fenwick 1985). Homer, the Greek poet from the eighth century B. C., worked garlic into his tales (Hedrick 1972), including a description of how Odysseus fended off Circe’s magic using as antidote a plant “having black root and milk white flower” (Fenwick and Hanley 1985a: 202).Tradition has it that this plant was wild garlic (Fenwick and Hanley 1985a).
Hippocrates (c. 460-370 B. C.) recommended garlic for pneumonia and suppurating wounds, but warned that it “caused flatulence, a feeling of warmth on the chest and a heavy sensation in the head; it excites anxiety and increases any pain which may be present. Nevertheless, it has the good quality that it increases the secretion of urine” (Jones and Mann 1963; Warren 1970; Fenwick and Hanley 1985a: 202).
Asia. Garlic was introduced into China between 140 and 86 B. C.The Chinese word for garlic, suan, is written as a single character, which often indicates the antiquity of a word (Hyams 1971). A fifth-century Chinese treatise on agriculture (Ch’i-min-yao-shu) described the cultivation of suan along the Red River valley. Chinese leeks, shallots, and spring onions were also discussed, but garlic seems to have been the most important. In addition, tse suan - water garlic (Allium nipponicum L.) - was mentioned as both a pervasive weed and a cultivated plant (Li 1969). According to Marco Polo (c. A. D. 1254-1324), garlic was used as a complement to raw liver among the Chinese poor (Lucas 1966), and much mention is made of garlic in treatises written in China from the fifteenth to the eighteenth centuries (Hedrick 1972).
In India, an important fifth-century Sanskrit medical manuscript, the Charaka-Samhita, based on sources from perhaps five centuries earlier, attributed widespread curative properties to both garlic and onion. It was claimed that they possessed diuretic properties, were beneficial to the digestive tract, were good for the eyes, acted as heart stimulants, and had antirheumatic qualities (Fenwick and Hanley 1985a).
In the Ayurvedic (Sanskrit) and Unani Tibb (Greco-Arabic) systems, garlic has been employed both as a prophylactic and as a cure for a variety of diseases, including arteriosclerosis, cholera, colic, dysentery, dyspepsia, gastric and intestinal catarrh, and typhoid. Duodenal ulcers, laryngeal tuberculosis, and lupus have all been treated with garlic juice, and garlic preparations have been given for bronchiectasis, gangrene of the lung, pulmonary phthisis, and whooping cough (Fenwick and Hanley 1985a).
Today the use of garlic is especially prevalent in Asia, where garlic-based antibiotics are used extensively to replace or complement more sophisticated drugs (Hanley and Fenwick 1985). In addition, in rural villages of Karnataka, in southwestern India, garlic is prescribed for lactating women (Rao 1985).
Europe. Garlic was regularly mentioned in European literature as well, especially for its medicinal benefits. The Roman poet Virgil (79-19 B. C.), for example, in his Second Idyll described how Thestylis used the juices of wild thyme and garlic as a prophylactic against snake bites (Warren 1970). A bit later, Pliny the Elder, in his Natural History, recommended that garlic be “placed when the moon is below the horizon and gathered when it is in conjunction” (Fenwick and Hanley 1985a: 200) to remove the plant’s pungent smell. He devised 61 garlic-based remedies for such conditions as hemorrhoids, loss of appetite, rheumatism, and ulcers (Jones and Mann 1963; Fenwick and Hanley 1985a).
The Romans apparently disliked garlic in general because of its strong scent, but it was fed to laborers to strengthen them and to soldiers to excite courage. The Romans also used garlic as a remedy for diabetes mellitus, and it is probable that it was similarly employed by the Egyptians and Greeks (Hanley and
Fenwick 1985). Carbonized garlic has been found at Pompeii and Herculaneum, which were destroyed in A. D. 79 (Meyer 1980).
The Greek military physician Dioscorides (A. D. 40-90) was clearly impressed with garlic, onion, and other alliums as medicinal plants. He advised garlic for baldness, birthmarks, dog and snake bites, eczema, leprosy, lice, nits, toothache, ulcers, and worms. He also suggested it as a vermifuge and diuretic and as a treatment for rashes and other skin disorders (Warren 1970; Fenwick and Hanley 1985a).
The cultivation of alliums in Western Europe is usually thought to have been stimulated by the Crusaders’ contacts with the East in the eleventh, twelfth, and thirteenth centuries. However, much earlier, Charlemagne (742-814) had listed garlic in his Capit-ulare de Villis and mentioned it as of Italian origin (Fenwick and Hanley 1985a). During medieval times, garlic was less appreciated for its taste than for its allegedly favorable effect on sexual potency and performance (Mauron 1986).
Presumably, however, the latter was of little interest to St. Hildegard (1098-1179), a German abbess, mystic, and scientific observer who continued the focus on garlic as medicine by specifically mentioning it in her Physica as a remedy against jaundice. The herbal doctors Paracelsus (Philippus Aureolus Paracelsus, 1493-1541) and Lonicerus (Adam Lonitzer, 1528-86) emphasized the antitoxic properties of garlic and its effectiveness against internal worms. At about the same time, Italian physician and botanist Matthiolus (Pietro Andrea Mattioli, 1500-77) was recommending garlic against stomach chills, colics, and flatulence.
The word “garlic” is derived from the old English “gar” (meaning spear) and, presumably, refers to the garlic clove. Geoffrey Chaucer (c. 1342-1400) wrote of “Wel loved garleek, onyons and leekes” (Fenwick and Hanley 1985a: 200), and garlic’s pungency was described by William Shakespeare. In A Midsummer Night’s Dream (Act IV, Scene 1), Bottom tells his fellow actors to eat neither garlic nor onion, “for we are to utter sweet breath,” and in Measure for Measure (Act III, Scene 2), Lucio criticizes the Duke, who “would mouth a beggar, though she smell brown bread and garlic.’A contemporary of Shakespeare described King Henry IV of France as “chewing garlic and having breath that would fell an ox at twenty paces” (Fenwick and Hanley 1985a: 201).
Garlic’s medicinal (and supposedly aphrodisiacal) powers were known in England in the sixteenth and seventeenth centuries, and the diarist Samuel Pepys (1633-1703) discovered that the custom in the French navy - to keep the sailors warm and prevent scurvy - was to issue garlic and brandy rations; the British Admiralty followed suit (Fenwick and Hanley 1985a).
At the turn of the nineteenth century, garlic in the form of inhalants, compresses, and ointments was used by the citizens of Dublin against tuberculosis, and the medicinal use of garlic is still common in Bulgaria, Japan, and Russia, among other places (Petkov 1986). In Russia, garlic-based antibiotics are widely employed, and on one occasion, 500 tonnes of garlic were imported to combat an outbreak of influenza (Fenwick and Hanley 1985a).
The Americas. Garlic was introduced to the Americas by the Spaniards. In Mexico, Cortes (1485-1547) apparently grew it, and by 1604, it was said in Peru that “the Indians esteem garlic above all the roots of Europe” (Hedrick 1972). By 1775, the Choctaw Indians of North America (Alabama, Louisiana, and Mississippi) were cultivating garlic in their gardens, and at the turn of the nineteenth century, American writers mentioned garlic as among their garden esculents (Hedrick 1972).
Garlic is widely used today in Latin America as a medicine as well as a food. In Guatemala, for example, it is prescribed for vaginitis by traditional healers, health promoters, and midwives (Giron et al. 1988) and is also employed against helminthic infection, both alone and in conjunction with commercial drugs (Booth, Johns, and Lopez-Palacios 1993). Argentine folk medicine prescribes garlic for antimicrobial use (Anesini and Perez 1993), and in the mountains of Chiapas in southeastern Mexico, Indian sheepherders use garlic and other alliums for veterinary purposes (Perezgrovas Garza 1990).
Production. The major producers of garlic in 1996 were (in metric tons) China (8,574,078), Korea (455,955), India (411,900), the United States (277,820), Egypt (255,500), and Spain (212,400), and world production was 11,633,800 metric tons. Major exporters in 1996 were China, Hong Kong, Singapore, Argentina, Spain, Mexico, and France, and major importers were Malaysia, Brazil, Indonesia, Singapore, the United Arab Emirates, Japan, the United States, and France.
In the United States, garlic production is confined mostly to California. Most of this crop is grown around the town of Gilroy, which calls itself the “garlic capital of the world” (Fenwick and Hanley 1985a).
Horticulture and Botany
Botany. Garlic is known only in its cultivated form but may be related to the wild Allium longicuspis of central Asia. Garlic bulbs develop entirely underground, and the plant is either nonflowering or flowers in the spring. Its leaves are flat and rather slender; the stem is smooth and solid. The bulbs are composed of several bulbils (cloves) encased in the white or pink skin of the parent bulb. Each clove is formed from two leaves, the outer cylindrical one being protective and the inner one a storage organ for the bud (Traub 1968).
Cultivation. Although it grows in a wide variety of soils, garlic flourishes best in rich, deep loams with plentiful moisture. Before planting, the bulbs should be dried, treated (e. g., with benomyl) to reduce rotting, and exposed to temperatures between 0° C and 10° C for four to eight weeks to ensure bulbing. Bulbs usually form and enlarge with long days and temperatures above 20° C. Plant spacing affects the size of the bulbs. Italian workers consider a spacing of 40 to 50 per square meter desirable. Doubling this density increases the yield by 50 percent, but then the bulbs are smaller and more suitable for processing than for the fresh market (Tesi and Ricci 1982). When the tops become dry and bend to the ground, harvesting is generally done by hand, although it can be done mechanically. Curing is usually carried out in the ground or in well-ventilated structures, and the dried bulbs can be stored.
Proper curing enables garlic to store well without careful temperature control. The best results are achieved when the bulbs are dried 8 to 10 days at 20° C to 30° C, followed by a reduction of temperature to 0° C with air circulation. Under these conditions, garlic bulbs can be stored from 130 to 220 days, depending on variety and how they were grown (IOS 1983).
Also effective in garlic storage is the application of maleic hydrazide prior to harvest (Omar and Arafa 1979), and gamma irradiation prevents storage losses without an adverse effect on taste, flavor, pungency, or texture (Mathur 1963). For cold storage conditions, it is recommended that garlic be harvested, dried, and packed away from all other crops except onions (Tesi and Ricci 1982).
Pathogens and Pests
The common pests and pathogens of garlic are those discussed in the section about onions.
Processing
Dehydrated garlic. As already mentioned, most of the garlic produced in the United States (90 percent) is grown and processed near the town of Gilroy, California. Gilroy also has the largest dehydration plant in the world, and in this region, more than 60,000 tons annually are processed into 25 different kinds of flakes, salts, and granules.
Dehydrated garlic can contain five times the flavor of the fresh clove, and garlic powder is used extensively in the manufacture of spiced sausages and other foods. To maintain flavor character and prevent lumping and hardening, the powder must be stored free of moisture. Flavor deterioration of stored garlic powder is maximal at 37° C and minimal between 0° C and 2° C. At room temperature, the product is best stored in cans. The packaging of garlic powder (at 6 percent moisture content) in hermetically sealed cans is best of all (Singh, Pruthi, Sankaran, et al. 1959; Singh, Pruthi, Sreenivasamurthy, et al. 1959).
Garlic flavoring. The volatile oil content of garlic is between 0.1 and 0.25 percent. The reddish-brown oil from the distillation of freshly crushed garlic cloves is rich in 2-propenyl sulfides. Often the oil itself is too pungent for efficient manufacturing use, so garlic juice - obtained in a similar manner to onion juice - is employed. Concentrating the juice produces oleo-resin garlic, a dark-brown extract with approximately 5 percent garlic oil. The oleoresin has uniformity, good handling, and good processing characteristics.
Nutrition
As with onions, the nutrient content of garlic changes with variety, ecological conditions, and climate. One hundred grams (3 53 ounces, or 0.44 of a cup) of garlic provides about 149 kilocalories of energy, 6.36 g of protein, 0.5 g of fat, and 33.07 g of carbohydrate (Nutrition Coordinating Center 1994).
In light of the RDA standard for males between 18 and 25 years of age, approximately one-half cup of fresh garlic (100 g) would provide them with 10.1 percent of the recommended dietary allowance of protein, 22.6 percent of calcium (181 mg), 17 percent of iron (1.7 mg), 19.1 percent of phosphorus (153 mg), 13.3 percent of copper (0.3 mg), 20.3 percent of selenium (14.2 mg), 52 percent of vitamin C (31.2 mg), 133 percent of thiamine (0.2 mg), 10.9 percent of pantothenic acid (0.6 mg), and 61.5 percent of vitamin B6 (1.23 mg). Garlic is high in potassium (401 mg/100 g), low in sodium (17 mg/100 g), and contains small amounts of magnesium, manganese, molybdenum, and zinc (Pruthi 1980; Raj et al. 1980). Other trace elements in garlic are cobalt, chromium, lithium, nickel, titanium, and vanadium. Garlic contains no vitamin A or E but does have small amounts of riboflavin, niacin, and folacin (National Research Council 1989).
Garlic (100 g) contains only small amounts of four fatty acids: 0.09 g of saturated palmitic acid, 0.01 g of monounsaturated oleic acid, 0.23 g of polyunsaturated essential linoleic acid, and 0.02 g of polyunsaturated essential linolenic acid. It has 4.1 g of dietary fiber, 14.7 g of starch, and 58.58 g of water. Sucrose (0.6 g), glucose (0.4 g), and fructose (0.6 g) are present, as are the essential amino acids - arginine (0.63 g) and glutamic acid (0.8 g) are the most abundant, followed by aspartic acid (0.49 g) and leucine (0.31 g).
Chemistry
Nonflavor compounds. Garlic contains polymers of fructose with up to 51 fructose molecules (Dar-byshire and Henry 1981). It also yields pectin. Garlic pectin content includes galactose, arabinose, galactur-onic acid, and glucose. It has a much higher viscosity than onion pectin, as well as a lower setting temperature and a longer setting time (Alexander and Sule-bele 1973; Khodzhaeva and Kondratenko 1983).
Sterols found in garlic are stigmasterol, B-sitosterol, and campesterol (Oka et al. 1974; Stoianova-lvanova, Tzutzulova, and Caputto 1980). Garlic also contains arachidonic and eicosapentaenic acids (Carson 1987).
Garlic has exhibited antioxidant activity in linoleic-acid and minced-pork model systems. This activity can be increased by microwave heating or boiling. It has been shown that S-alkenyl cysteine sulfoxides were the most active. Quercetin and other flavone agly-cones also contribute to the total antioxidant capacities of onion and garlic extracts (Pratt and Watts 1964; Naito et al. 1981a, 1981b).
Allithiamin, discovered in the 1950s by Japanese researchers, is formed in garlic from thiamine and allicin and is absorbed faster in the intestinal tract than thiamine (Fujiwara 1976). Unlike thiamine, allithiamin is not degraded by thiaminase and appears more stable under conditions of heat (Hanley and Fenwick 1985). Allithiamin, which reacts with the amino acid cysteine to regenerate thiamine - yielding 2-propenylthiocysteine - has been found effective against cyanide poisoning (Carson 1987).
Flavor compounds. The first important studies on the composition of garlic oil were carried out by T. Wertheim in 1844 and 1845. While investigating the antibacterial properties of garlic in the 1940s, C. J. Cavallito and others discovered the thiolsulfinate allicin, the most important flavor component of fresh garlic (Carson 1987). This colorless oil is di(2-propenyl)thiolsulfinate. (In this chapter, 2-propenyl is used instead of allyl.) Allicin is probably the first thiolsulfinate isolated from natural sources (Carson 1987).
The compounds responsible for the flavor of alliums are produced from involatile precursors only when tissue maceration occurs. Gamma-glutamyl peptides, containing approximately 90 percent of garlic’s soluble, organically bound sulfur, are present in significant amounts and may be the storage form of the flavor precursors (Virtanen 1965;Whitaker 1976). Under these circumstances, alkyl or alkenyl cysteine sulfoxides come into contact with an enzyme, alliinase, and hydrolysis occurs. The initially formed thiolsulfi-nates can break down to produce a range of organoleptically important sulfur compounds, including disulfides, trisulfides, higher sulfides, and thiols. The flavor properties of the different alliums depend on the types and amounts of these sulfur compounds (Hanley and Fenwick 1985).
Over 90 percent of the flavor-precursor content of garlic is located in the storage leaf (Freeman 1975). Alliin lyase is a major product of the storage bud (clove), accounting for 10 percent of its total protein. Deposits of alliinase are most pronounced around phloem tissue and are concentrated in the bundle sheaths. Little, if any, occurs in storage mesophyll that is not in contact with vascular bundles. This deposition in the clove may reflect the enzyme’s role in protecting underground storage buds from decay and predation. Positioning near the phloem suggests that alliin lyase, or compounds related to its activity, may be translocated to and from the clove during development (Ellmore and Feldberg 1994).Alliinase is present in most, if not all, members of the genus Allium, and is also found in Albizzia, Acacia, Parkia, and Lenti-nus species.
Medicinal Use
Atherosclerotic. Medical claims for the efficacy of garlic against myriad complaints have been made for millennia and are still being made today as science continues to analyze the properties of this tasty vegetable and channel them to medical use.
The second-century Indian physician, Charaka, reported that onion and garlic prevented heart disease and acted as heart tonics (Fenwick and Hanley 1985c). Clots, which can cause strokes and heart attacks, are formed through the aggregation of platelets. Both garlic and onion have a demonstrated ability to inhibit platelet aggregation, possibly by interfering with prostaglandin biosynthesis (Ali et al. 1993).
In a double-blind, placebo-controlled study of 60 volunteers with cerebrovascular risk factors and constantly increased platelet aggregation, it was demonstrated that daily ingestion of 800 mg of powdered garlic (in the form of coated tablets), over four weeks, significantly decreased the ratio of circulating platelet aggregates and inhibited spontaneous platelet aggregation. The ratio of circulating platelet aggregates decreased by 10.3 percent; spontaneous platelet aggregation decreased by 56.3 percent (Kiesewetter et al. 1993).
Some garlic compounds that inhibit platelet aggregation have been identified. These are methyl (2-propenyl)trisulfide (the strongest), methyl (2-propenyl)disulfide, di(2-propenyl)disulfide, and di(2-propenyl)trisulfides. All these compounds are said to be formed from allicin, which is di (2-propenyl)thiosulfinate. There is some evidence that methyl(2-propenyl)trisulfide is more effective on a molar basis than aspirin (Makheja, Vanderhoek, and Bailey 1979; Ariga, Oshiba, and Tamada 1981; Bosia et al. 1983; Apitz-Castro, Badimon, and Badimon 1992; Lawson, Ransom, and Hughes 1992). Recently, a novel amino acid glycoside, (-)-N-(1'-beta-D-fructopyranosyl)-S-2-propenyl-L-cysteine sulfoxide, showed significant inhibition of in vitro platelet aggregation induced by ADP (adenosin diphosphate) and epinephrine (Mutsch-Eckner et al. 1993).
Garlic has also been shown to increase fibrinolytic activity, which inhibits clot formation (Bordia et al. 1978). An excellent epidemiological study of garlic and onion intake in the Jain community in India was done in 1979. Three groups with widely differing allium consumption patterns were chosen: those who had always abstained from onions and garlic; those who consumed only small amounts (<200 g onion, <10 g garlic per week); and those who consumed onions and garlic liberally (>600 g onion, >50 g garlic per week). The three groups were otherwise similar in regard to intake of calories, fat, and carbohydrates. Those who ingested the most alliums had the lowest level of plasma fibrinogen, which is used by the body in forming a blood clot with platelets (Sainani, Desai, Natu et al. 1979).
In a study of dried garlic consumption by 20 patients with hyperlipoproteinemia over a period of four weeks, fibrinogen and fibrinopeptide A significantly decreased by 10 percent. Serum cholesterol levels significantly decreased by 10 percent. Systolic and diastolic blood pressure decreased. ADP - and collagen-induced platelet aggregation were not influenced (Harenberg, Giese, and Zimmermann 1988).
The antithrombotic agents found in garlic that we know about are (E, Z)-ajoene, or (E, Z)4,5,9-trithiado-deca-1,6,11-triene 9-oxide, the major anticoagulant, di(2-propenyl)trisulfide, and 2-vinyl-4H-1,3-dithiene (Apitz-Castro et al. 1983; Block et al. 1984; Block 1992).
It is generally known that both fresh and boiled garlic decrease cholesterol and triglycerides. The Jain epidemiological study, mentioned previously, demonstrated not only that liberal use of onions and garlic decreased total cholesterol, low-density lipoprotein (LDL - the so-called bad cholesterol), and triglycerides, but also that those who consumed even small amounts of alliums were better protected than those who ate no onions or garlic (Sainani, Desai, Gorhe, et al. 1979).
One study, however, found that garlic increased cholesterol in people who had suffered a heart attack. A longer-term trial of garlic’s effects on these people was undertaken and lasted 10 months. After 1 month, there was an increase in cholesterol, but thereafter it decreased, and after 8 months, it had declined by 18 percent. The initial increase in serum cholesterol in the heart patients who were fed garlic may have been caused by mobilization of lipid from deposits. Decreases of LDL occurred, and high-density lipoprotein (HDL - the “good” cholesterol) increased (Bordia 1981).
A multicentric, placebo-controlled, randomized study of standardized garlic-powder tablets in the treatment of hyperlipidemia (cholesterol levels over 200 mg/dl) was performed over a 16-week period. The total intake of garlic powder was 800 mg/day, standardized to 1.3 percent of alliin, (+)S-(2-propenyl)-L-cysteine, content (Stoll and Seebeck 1948). Cholesterol levels dropped 12 percent and triglyceride levels dropped 17 percent, with the best lowering effects seen in patients with cholesterol values between 250 to 300 mg/dl (Mader 1990).
World History
