Latin name: Ceratonia siliqua
Common names: Carob bean gum, Carob, Carob-tree, Locust bean, St John's Bread
A food additive, which may result in allergy symptoms in sensitised individuals.
Allergen ExposureGeographical distribution
Carob is an evergreen tree probably native to the Middle East. It is related to Mesquite, Acacia and Tragacanth trees. Cultivated since antiquity in hot, semiarid regions, it serves as an important forage crop. The Greeks diffused it in Greece and Italy, but it was afterwards more highly esteemed by the Arabs. The products of the tree, especially the powder from the pods, are in widespread use both near the tree’s habitats and throughout the industrialised world.
The sugary, edible pods produced by some species resemble Locusts—hence the name Locust bean. As St John the Baptist fed on “honey and locusts”, the pod also became known as St John's bread.
Both fresh and dried Carob pods, as well as Carob powder, may be found in health-food and specialty food stores. The long, leathery pods from the Carob tree contain a sweet, edible pulp (which can be eaten fresh). After drying, the pulp is roasted and ground into a powder, used in making preserves, juices, and liqueurs, as an ingredient in cosmetics, and as a flavouring for cigarettes. It is also used to flavour baked goods and candies. Grinding the pod and pulp together makes Carob powder. Because Carob is sweet and tastes vaguely of chocolate, it is often used as a chocolate substitute, with coconut oil or hydrogenated vegetable oil added.
An edible gum, Locust bean gum, a substitute for Gum Tragacanth, is extracted from the seed and called in the trade "Tragasol”. A stabiliser and thickening agent, it is also used as an egg substitute. The roasted seed is a coffee substitute and contains no caffeine. Flour from the pods is used in making bread, pancakes, breakfast cereal and syrup. The sugars can produce fungal protein and alcoholic beverages.
Various parts and preparations of the plant are used to treat constipation, hypercolesterolemia, diarrhoea and coughs. The seed residue after gum extraction can be made into a starch- and sugar-free flour of 60% protein content for diabetics.
The pods are used as an animal feed. Great quantities of pods have been imported into the United States for flavouring uncured tobacco. Carob is an additive in breakfast foods such as jams, marmalades, and yoghurt. It is used in cake icing, canned poultry and meats, infant food, prepared mustard, and some toothpaste. Carob thus has the status of a “hidden allergen”.
The seed gum is employed in the manufacture of cosmetics, pharmaceutical products, detergents, paint, ink, shoe polish, adhesives, sizing for textiles, photographic paper, insecticides and match heads. It is also utilised in tanning. Where Rubber Latex is produced, the gum is added to cause the solids to rise to the surface. It is also used for bonding paper pulp and thickening silkscreen pastes, and some derivatives are added to drilling mud. The wood is used for turnery, cabinetwork and fuel. Tannin is obtained from the bark.
No allergens from Carob have yet been fully characterised, although allergens in the 17.5, 48, and 66 kDa MW bands were identified. Heat-processing deactivates Carob protein allergenicity. This has dietary implications for polyallergic children (1).
Potential Cross-ReactivityAn extensive cross-reactivity among the different individual species of the genus could be expected but in fact is not seen frequently (2). 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 between the extracts of Peanut, Garden pea, Chick pea, and Soybean (3).
However, clinical studies have found that there is little cross-reactivity between members of the legume family (4-5). Specifically, there is no cross-allergenicity between Carob and Peanut. Twelve patients with a history of anaphylaxis to Peanut were skin-prick tested with Peanut allergen, raw Carob pulp, and raw and cooked Carob cotyledon formula. RAST for Peanuts and cooked Carob were performed and Carob-specific IgE identified by immunoblotting analyses. Allergic reactivity was evaluated during double-blind-placebo-controlled-challenges (DBPCFC) to 5.5 g Carob extract and cooked Carob cotyledon formula. Peanut allergen-induced skin prick test was positive in all children, Carob pulp in 3/12 patients, raw Carob bean in 6/12, and cooked Carob cotyledon formula in none. RAST were positive for Peanut in all cases but negative for Carob beans in 9/12 cases. Immunoblot analyses found Peanut-specific IgE in all cases and raw Carob bean-specific IgE in 8 cases. There was no clinical reactivity with either raw or cooked Carob during DBPCFC (1).
Guar gum and Carob bean flour are both derived from Leguminosae plants. The molecular structures of carob bean and guar gum are very similar, consisting of a high molecular weight polysaccharide. Allergic reactions to Guar gum have been reported (6). Some degree of cross-reactivity between these plants may be possible.
Clinical ExperienceIgE-mediated reactions
Carob/Carob gum may uncommonly induce symptoms of food allergy in sensitised individuals.
Allergy to Carob gum has been reported in an infant. A 5-month-old child with gastroesophageal reflux (GER) was found to be allergic to an anti-regurgitation milk formula containing Carob gum as a thickening agent. She developed explosive vomiting, urticaria, and a rash on her face soon after the onset of her first feed (7).
Occupational allergy to Carob has been reported. Asthma and rhinitis to Carob bean flour has been described in a man who handled Carob bean flour as part of his work in a jam factory. After 2 years in his job, he complained of work-related rhinitis and irritated eyes. Asthma appeared 3 years later. Symptoms disappeared over weekends. Biochemical evidence suggested that the allergy was IgE-mediated (8). Similarly, rhinitis and asthma were described in a man who routinely handled Carob bean flour as part of his work as an ice cream maker. Skin and serum specific IgE were both positive (9).
Pollen from the Carob tree was reported to be an important inhalant allergen in Turkey (10).
Carob bean gum is used as a thickener in foods and infant foods. This thickener could cause loose, gelatinous stools of sufficient frequency to warrant temporary withdrawal (11). Furthermore, the ingestion of Carob bean gum has been shown to cause a significant reduction in the absorption of calcium, iron, and zinc (12-13). Also, the pods contain up to 1.5% tannins, which may interfere with the body's utilisation of protein.
Carob pods and leaves contains a valium-like substance that binds with central and peripheral benzodiazepine receptors. The amount of the substances recovered from Carob pods and leaves was respectively 12.17 and 18.7 ng diazepam equivalent/g. The compounds acting on peripheral benzodiazepine receptors were found to be extremely concentrated in the young leaves (14).
- Fiocchi A, Restani P, Travaini M, Decet E, Gaiaschi A, Bernardo L, Riva E. Carob is not allergenic in peanut-allergic subjects. Clin Exp Allergy 1999;29(3):402-6
- Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09
- 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
- 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
- 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
- Lagier F, Cartier A, Somer J, Dolovich J, et al. Occupational asthma caused by guar gum J Allergy Clin Immunol 1990;85:785-790
- Savino F, Muratore MC, Silvestro L, Oggero R, Mostert M. Allergy to carob gum in an infant. J Pediatr Gastroenterol Nutr 1999;29(4):475-6
- van der Brempt X, Ledent C, Mairesse M. Rhinitis and asthma caused by occupational exposure to carob bean flour. J Allergy Clin Immunol 1992;90(6 Pt 1):1008-10
- Scoditti A, Peluso P, Pezzuto R, Giordano T, Melica A. Asthma to carob bean flour. [Letter] Ann Allergy Asthma Immunol 1996;77(1):81
- Guneser S, Atici A, Cengizler I, Alparslan N. Inhalant allergens: as a cause of respiratory allergy in east Mediterranean area, Turkey. Allergol Immunopathol (Madr) 1996;24(3):116-9
- Carré IJ. Management of gastroesophageal reflux. Arch Dis Child 1985;60:71-5.
- Bosscher D, Robberecht H, Van Cauwenbergh R, Van Caillie-Bertrand M, Deelstra H. Binding of mineral elements to locust bean gum influences availability in vitro. Biol Trace Elem Res 2001;81(1):79-92
- Bosscher D, Van Caillie-Bertrand M, Deelstra H. Effect of thickening agents, based on soluble dietary fiber, on the availability of calcium, iron, and zinc from infant formulas. Nutrition 2001;17(7-8):614-8
- Avallone R, Cosenza F, Farina F, Baraldi C, Baraldi M. Extraction and purification from Ceratonia siliqua of compounds acting on central and peripheral benzodiazepine receptors. Fitoterapia 2002;73(5):390-6