Latin name: Allium sativum
Source material: Garlic powder
Family: Alliaceae (Liliaceae)
Common names: Garlic, Cultivated garlic, Poor Man's treacle
Garlic is a small, very pungent Onion-like plant. It has been used for millennia (it was mentioned in 1550 BC) as a flavouring and a medicine, and is now important in many cuisines worldwide. In some parts of the world, Garlic’s use also has religious connotations.
Only a few members of this family are important as food plants, notably Onion, Garlic, Chive, Leek, and Rakkyo. Garlic’s edible bulb or “head” grows beneath the ground. This bulb is made up of sections called cloves, each encased in its own parchment-like membrane. Today’s major Garlic suppliers include the United States (mainly California, Texas and Louisiana), France, Spain, Italy and Mexico. There are several major types of Garlic available, with cloves up to 6 cm in diameter. The flavours, in addition to being characteristic, are complex, as they are derived enzymatically from a number of involatile precursors. Fresh Garlic is available year-round.
Garlic grows in cultivated beds, with occasional escapes. Garlic bulbs are eaten, either raw or cooked, as flavouring.. They are usually peeled before use in recipes. Crushing, chopping, pressing or pureeing Garlic releases more of its essential oils and provides a sharper, more assertive flavour than slicing or leaving it whole. Garlic is readily available in forms other than fresh, such as dehydrated flakes or powder. Garlic salt is Garlic powder blended with salt and a moisture-absorbing agent. Garlic extract and Garlic juice are derived from pressed Garlic cloves. One unfortunate side-effect of Garlic is that, because its essential oils permeate the lung tissue, it remains with the body long after it has been consumed, affecting breath and even skin odour. The stems, leaves, flowers and seed can be eaten raw or cooked, and are rather milder than the bulbs.
Garlic can reduce nasal congestion and lower blood pressure and blood cholesterol (for example, demographic studies suggest that Garlic is responsible for the low incidence of arteriosclerosis in areas of Italy and Spain where consumption of the bulb is heavy). It has been employed as an antiviral, antibacterial, fungicidal, vermifuge, vasodilator, expectorant, diuretic, antiasthmatic, antispasmodic, febrifuge, stomachic, skin-soothing, tonic, and immunostimulant agent. It may, however, induce migraines. Garlic extract inhibits chromosomal breaks due to sodium arsenite (arsenic), a contaminant in ground water. It has been shown that Garlic aids detoxification of chronic lead poisoning. It is also said to have anticancer activity. Recent research has indicated that Garlic reduces glucose metabolism in diabetics.
The growing plant is said to repel insects, rabbits and moles. An extract of the plant can be used as an insect repellent.
Cloves of Garlic are sometimes spread among stored fruit to delay rotting. The juice is also used as glue for mending glass and china.
No allergens from this plant have yet been characterised.
Using serum from a Garlic-allergic individual, a 12 kDa protein band to young Garlic, mature Garlic, Onion, and Leek extracts was detected. Similar bands could also be detected with Mugwort pollen and Hazelnut extract (1).
Protein bands of 10, 20 and 40 kDa were detected in a patient with urticaria who was affected by cooked and raw Onions. Garlic appears to have heat-stabile and heat-labile allergens (2).
A 12 kDa and a 40-50 kDa protein have been detected (3), probably corresponding to a mannose-binding lectin (4) and alliinase (5) respectively, both previously reported and probably heat-labile.
In a patient with nasal symptoms following exposure to Garlic dust, significant protein bands at 14 and 40 kDa to Garlic extract were demonstrated (6).
In a study of 15 patients with Garlic allergy, with symptoms of rhinitis, urticaria, dermatitis, and asthma, IgE-binding components ranging from 31 to 60 kDa were isolated. A component with a molecular weight of approximately 56 kDa was detected by all 15 sera and identified as alliin lyase. Other IgE-binding components of various molecular weights were detected at frequencies of less than 30%; for example, 4 serum samples gave a positive reaction to a 42 kDa component. Periodate oxidation showed that carbohydrate groups were involved in the substance’s antigenicity, allergenicity, and cross-reactivity (7).
An extensive cross-reactivity among the different individual species of the genus could be expected, as well as to a certain degree among members of the family Alliaceae (previously categorised as Liliaceae), such as Onion, Leek, Garlic, Asparagus and Chives (8-9).
The major Garlic allergen, alliin lyase, showed strong cross-reactivity with alliin lyases from other Allium species, namely Leek, shallot, and Onion (7).
Cross-allergenicity between Garlic and other members of the Liliaceae family was documented through the RAST inhibition technique (10).
The presence of structurally similar allergens in Garlic, Onion, and certain pollens of Phleum and Chenopodium has been described. There was partial abolishment of the IgE binding to several of these allergens (11). The clinical significance of this is not yet known.
Garlic can induce symptoms of food allergy in sensitised individuals (12-13). Garlic is well-known cause of contact dermatitis and asthma. However, it is thought to be an uncommon cause of food or other allergy in children (1-2,14-16). In a European study of 589 individuals with food allergy, SPT positivity to Liliaceae (Garlic, Onion, Chive) was documented in 4.6% of children and 7.7% of adults (17).
In an evaluation of 163 asthmatic French children with food allergy who were assessed for food-induced asthma using DBPCFC, the most frequent offending foods were, sometimes in association, Peanut (30.6%), Hen’s egg (23.1%), Cow’s milk (9.3%), Mustard (6.9%), Codfish (6%), Shrimp (4.5%), Kiwi fruit (3.6%), Hazelnut (2.7%), Cashew nut (2.1%), Almond (1.5%), and Garlic (1.2%) (18). A subsequent study was done by the same main author of a cross-sectional, descriptive, questionnaire-based survey conducted in Toulouse schools in France to determine the prevalence of food allergies among schoolchildren; it was reported that, out of 2,716 respondents, 192 self-reported a food allergy, but that there was only a single reported case of allergy to Garlic (19).
A study was conducted at 17 clinics in 15 European cities to evaluate the differences among some northern countries regarding what foods, according to food-allergic patients, elicit hypersensitivity symptoms. It was reported, after evaluation of questionnaires concerning 86 different foods, that the foods apparently most often eliciting symptoms in Russia, Estonia, and Lithuania were citrus fruits, chocolate, honey, Apple, Hazelnut, Strawberry, fish, Tomato, Hen’s egg, and Milk; these results differed from those of Sweden and Denmark, where Birch pollen-related foods, such as nuts, Apple, Pear, Kiwi, stone fruits, and Carrot, were the most common reported causes. The most common symptoms reported were oral allergy syndrome and urticaria. Birch pollen-related foods apparently dominated as allergens in Scandinavia, whereas some Mugwort-related foods seemed to be of more importance in Russia and the Baltic States. Among 1,139 individuals, Garlic was the 57th most reported food allergen, resulting in adverse effects in 8.2% (20).
In an Indian study of 24 children aged 3 to 15 who had documented deterioration in control of their perennial asthma, IgE antibodies to Garlic were documented in 14 (58%) (21).
A large population-based study of adverse reactions to food in adults in Istanbul found Garlic to be an uncommon self-reported cause of adverse reactions (22).
A study described a small population of patients in the mid-southern region of Taiwan who were allergic to Garlic. Symptoms included rhinitis, urticaria, dermatitis, and asthma. All the patients had lived near Garlic fields, worked or played near a Garlic store, and eaten Garlic over a long period of time. Serum samples were obtained from all 15 patients, and the allergen alliin lyase was identified in all. All 12 patients were positive on intradermal testing with purified Garlic alliin lyase, whereas 58% were positive with a lower concentration (7).
A 16-month-old boy with a history of Cow’s milk and Hen’s egg white allergy has been reported as developing urticaria on the face and neck immediately after contact with fresh Garlic. He tolerated cooked Garlic (3).
Garlic may result in anaphylactic reactions, as described in a 23-year-old woman who had eaten young Garlic (1).
Occupational asthma and rhinitis have been reported, which may have an onset long after work with the substance (11,23-24). Occupational allergy to Garlic dust has also been reported (25-26). In an atopic patient, repeated exposure to Garlic dust induced severe asthma. The patient subsequently also developed marked adverse responses after ingesting Garlic. A skin prick test and a bronchial challenge test with Garlic dust and extract were both positive, as was an oral challenge test with Garlic dust. Serum Garlic-specific IgE was unusually high (10).
A study reported on a patient who presented with nasal symptoms when working with spices that included Garlic and Onion dust. Skin prick tests were positive for Onion, Garlic powder and fresh Liliacea (not specified). IgE antibody levels were found to Garlic and Onion, and significant protein bands at 14 and 40 kDa with Garlic extract were demonstrated. Nasal challenge showed an increase in inspiratory nasal resistance that was higher than 100% of the basal value for both Onion extract and Garlic (6).
Allergic contact dermatitis to Garlic has a typical clinical presentation, but this is often masked if the reaction presents concurrently with another form of hand dermatitis or other conditions (27-29). Reactions may be immediate or delayed (30). Occupational airborne allergic contact dermatitis from Garlic has been reported (31).
Allergic contact cheilitis to Garlic has been described (32).
The spectrum of Garlic-related skin adverse reactions comprises irritant contact dermatitis (with the rare variant of zosteriform dermatitis), pemphigus, contact urticaria, protein contact dermatitis, and allergic contact dermatitis, as well as combinations of these (33-34).
Garlic is a common cause of contact dermatitis, in particular in an occupational environment (35-39). Contact dermatitis from Garlic is usually due to handling of Garlic for cooking, especially in the cases of greengrocers, housewives and cooks (40-43). In India, Garlic was reported to be the offending agent in 6.7% of patients seen with contact dermatitis (44). Occupational contact dermatitis from a Garlic and herb mixture has been described (45). Garlic-induced systemic contact dermatitis has also been reported (46). Garlic-sensitive patients showed positive tests to diallyldisulfide, allylpropyldisulfide, allylmercaptan and allicin, all present in Garlic (47).
Patients have experienced second-degree burns of the forehead, breast, and other parts of the body, induced by topical application of crushed Garlic (48-50). These burns may mimic herpes zoster (51). Children have also been adversely affected by poultices containing Garlic (52).
A case of superficial pemphigus has been reported as appearing spontaneously in a 49-year-old man and running a course that proved to be affected by dietary factors, in particular by the consumption of Garlic (53).
Compiled by Dr Harris Steinman, email@example.com
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