Tragacanth gum

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Code: f298
Latin name: Astragalus gummifer
Family: Fabaceae (Leguminosae)
Common names: Tracacanth gum, Tragacanth
Food
A food, which may result in allergy symptoms in sensitised individuals.

Allergen Exposure

Geographical distribution
Tragacanth gum is one of oldest known natural emulsifiers, predating Christ. The substance is an exudate obtained from the Astragalus species of shrub, an evergreen growing to 0.3m by 0.3m, which is found in Iran, Asia Minor and Syria. Tragacanth collection is usually similar to that of Latex/rubber, through man-made incisions in the lower stem and root (though some natural exudation takes place). The resulting gum is considered to be the most viscous of the plant gums.
 
Environment
Tragacanth is used as a thickener, stabiliser and emulsifier in candy, salad dressings, sauces, fruit jelly, ornamental icings, fruit sherbets, etc. It is an approved additive to food and has the E number E413. The seedpods of some species may be eaten, but those of others are toxic (see under Other reactions).
 
The gum is demulcent, though it is not often used internally because it is not completely soluble. It has long been employed externally as a dressing for burns. This gum has recently been shown to stimulate the immune system and to suppress tumours. Tragacanth tends to decrease absorption of cholesterol into the system if taken with cholesterol-rich foods.
 
Unexpected exposure
Like gum Arabic, Tragacanth gum has a wide range of non-food uses, including as a thickener, stabiliser and emulsifier in shaving cream, toothpaste, face packs, creams, and eye makeup, as a fabric dressing, and as a thickening agent in dyes, glues, water colours and ink. It is a binding agent in paper making, a culture medium in laboratories, etc. It is commonly used in lozenges in order to bind the ingredients and impart consistency. Both the stems and the gum can be burnt as incense.
 
Allergens
No allergens from this plant have yet been characterised.

Potential Cross-Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected but in fact is not seen frequently (1). In an in vitro study, the specific IgE binding by protein extracts of 11 food legumes was examined by RAST and RAST inhibition. Cross-allergenicity was demonstrated to be most marked among the extracts of Peanut, Garden pea, Chick pea, and Soybean (2-3).
 
However, clinical studies have found that there is little cross-reactivity among members of the Fabaceae (Leguminosae) (4-6).
 
Cross-reactivity between Acacia gum and Tragacanth gum has been reported (7).

Clinical Experience

IgE-mediated reactions
Tragacanth gum may rarely induce allergy symptoms in sensitised individuals. Asthma and contact dermatitis have been described (8-11).
 
Excess ingestion can result in diarrhoea, abdominal pain, gas production or constipation.
 
Other reactions
Many members of this genus contain toxic glycosides. All species with edible seedpods can be distinguished by their fleshy round or oval seedpod that looks somewhat like a Greengage. A number of species can also accumulate toxic levels of selenium when grown in soils that are relatively rich in that element.
 
Compiled by Dr Harris Steinman, harris@zingsolutions.com

References

  1. Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09
  2. Barnett D, Bonham B, Howden ME. Allergenic cross-reactions among legume foods--an in vitro study. J Allergy Clin Immunol 1987;79(3):433-8
  3. Bardare M, Magnolfi C, Zani G. Soy sensitivity: personal observation on 71 children with food intolerance. Allerg Immunol (Paris) 1988;20(2):63-6
  4. Bernhisel Broadbent J, Sampson HA. Cross-allergenicity in the legume botanical family in children with food hypersensitivity. J Allergy Clin Immunol 1989;83:435-440
  5. Bernhisel-Broadbent J, Taylor S, Sampson HA. Cross-allergenicity in the legume botanical family in children with food hypersensitivity. II. Laboratory correlates. J Allergy Clin Immunol 1989;84(5 Pt 1):701-9
  6. Eigenmann PA, Burks AW, Bannon GA, Sampson HA. Identification of unique peanut and soy allergens in sera adsorbed with cross-reacting antibodies. J Allergy Clin Immunol 1996;98(5 Pt 1):969-78
  7. Raghuprasad PK, Brooks SM, Litwin A, Edwards JJ, Bernstein IL, Gallagher J. Quillaja bark (soapbark)--induced asthma. J Allergy Clin Immunol 1980;65(4):285-7
  8. Brown EB, Crepea SB. Allergy (asthma) to ingested gum tragacanth. J Allergy 1947;18:214-216
  9. Gelfand, HH. Allergenic properties of the vegetable gums. J Allergy 1943;14:203-219
  10. Yeates H, Jenson, K, Orem, UT. Chronic anaphylaxis caused by ingestion of vegetable gum products. J Allergy Clin Immunol 1991;87(Suppl 1 Pt 2):274.
  11. Yman L, Rolfsen, W, Malmheden Yman, I. Food additives from the legume family (Leguminosae/Fabaceae): A potential allergy risk. Allergy 1988;81:H-17/81

 

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.