Latin name: Bertholletia excelsa
Source material: Shelled nuts
Common names: Brazil nut, Para-nut, Cream nut
The Brazil nut is actually the seed of a giant tree that grows wild in South America's Amazon jungle. The seeds, about 6 cm long, come in clusters of 8 to 25 inside a large, hard, thick-walled globular pod that resembles a Coconut and weighs up to 2 kg. The extremely hard shell of each seed is dark-brown and 3-sided. The kernel is white and high in oil, containing about 70% oil and 17% protein. When fresh it is highly esteemed for its rich flavour, but it becomes rancid in a short time from the great quantity of oil it contains. Except for its close relative the Paradise nut, it is not closely related to any other food.
Brazil nut exportation from the Amazon was begun in the 1600s by Dutch and Portuguese traders. The monetary value of the nuts (nearly all from wild trees) is second only to that of rubber.
In the Amazon, indigenous tribes eat the nuts raw, or grate them and mix them into gruels, often along with Manioc flour. The plentiful oil is used in cooking. Exported, the nuts are a snack food, and their oil is prized. In addition to protein and fat, Brazil nuts are a substantial source of selenium, an important antioxidant. The proteins, though making up only 15-17% of the nuts' fresh weight, comprise 50% of the defatted flour. Storage proteins are the most important ones, and the 12S globulin legumin-like protein and the 2S albumin have been identified as the most representative. The 2S protein is high in sulfur-rich amino acid (3-8% cysteine and 18% methionine) (1). The proteins are also extremely rich in glutamine, glutamic acid, and arginine.
The tree bark is brewed into tea to treat liver ailments. The husks of the seed pods have also been brewed to treat stomach aches.
Brazil nut may be a "hidden" allergen in cookies, etc. The oil extracted from the nuts is commonly used in Peru and other South American countries to manufacture soap, and for lighting, and the empty pods are used as implements and burned to repel insects. Worldwide, Brazil nut oil is often used in soaps, shampoos, hair conditioning/repair products, and skin moisturisers, and extracts of the pods can figure in insect repellents.
A number of allergenic proteins has been isolated from Brazil nut. These range in size from 4 kDa to 58 kDa. In a study of a group of patients with IgE antibodies to Brazil nut, comprising 11 patients with anaphylaxis to eating Brazil nuts and 10 asymptomatic subjects, sera from all the symptomatic patients recognised a 9 kDa allergen corresponding to 2S albumin of Brazil nut, whereas the other allergens each bound IgE antibodies from less than 50% of sera. No IgE binding to the 9 kDa allergen occurred in sera from asymptomatic subjects, but allergenic proteins of 25 to 58 kDa were recognised and were identified as minor allergens (5). Other minor allergens have been detected: of 18, 25, 33, and 45 kDa (2), including a 12S globulin protein, which is a legumin-like storage globulin (1).
The allergens characterised to date are:
- Ber e 1, a 9 kDa protein, a 2S albumin, resistant to digestion by pepsin, and a major allergen (3-14).
- Ber e 2, an 11S globulin-like protein (10,13,15).
The main immunoglobulin E epitope region of the 2S albumin, Ber e 1, is very stable to gastric digestion (3,8,16).
The Brazil nut 2S albumin has been recognised as a methionine-rich protein that could be used to increase the nutritional value of certain foods through genetic engineering techniques. However, the 2S albumin of the Brazil nut is also the major allergen of Brazil nuts (Ber e 1) and shows IgE-reactivity with more than 80% of the sera from Brazil nut-allergic subjects. This was demonstrated in transgenic Soybean: the newly expressed protein retained its allergenicity (17-18).
An extensive cross-reactivity within the family can be expected (19).
Brazil nut contains a 2S albumin storage protein, a protein common to many seeds, which displays similarity to the 2S albumin of Cotton, Cocoa bean, Sunflower seed, Rape seed, Castor bean, English walnut (Jug r 1), Mustard seed (Sin a 1) and Sesame seed (Ses i 2). Comparison of the amino acid sequence shows high sequence similarity, from 34% between Sunflower seed and Brazil nut, to >52% similarity and >38% identity between Brazil nut and many other plant 2S albumins (20-24). The English walnut allergen (Jug r 1) exhibits a 46.1% identity with the Brazil nut 2S albumin seed storage protein, Ber e 1 (24-25).
The 2S albumins have been shown to play a significant role in cross-reactivity between Walnut Jug r 1 and Pecan nut Car i 1, as a result of the high degree of structural homology of the 2S albumins in these 2 tree nuts. However, a study of the con-formational analysis of the linear IgE-binding epitopes mapped on the molecular surface of Ara h 2, a 2S albumin, showed no structural homology with the corresponding region of Brazil nut Ber e 1; this indicates that allergenic cross-reactivity observed between Peanut and Brazil nut may depend on other ubiquitous seed storage protein allergens, e.g., the vicilins (26).
However, a recent study evaluating cloned Peanut Ara h 2 reported that when serum from Peanut-allergic patients is pre-incubated with increasing concentrations of Almond or Brazil nut extract, IgE binding to rAra h 2 is inhibited. Purified rAra h 2-specific serum IgE antibodies also bound to proteins present in Almond and Brazil nut extracts through immunoblotting, which indicates that the Peanut allergen Ara h 2 shares IgE-binding epitopes with both Almond and Brazil nut allergens (27). The same authors had previously reported that Peanut-specific antibodies from sera of Peanut-allergic subjects became activated following stimulation with Peanut, Almond and Brazil nut extracts, demonstrating biological activity of cross-reactive IgE antibodies (28).
A 2S albumin has been isolated from the seed of Tomato and was found to cross-react with antiserum to the fruit lectin. The sequence of the fruit lectin was shown to be similar to that of 2S albumins from different plants, such as Brazil nut and Castor beans (29). The allergenicity of the Tomato seed 2S albumin was not evaluated.
Walnut-induced anaphylaxis has been reported, with cross-reactivity to Hazel nut and Brazil nut described (30).
Allergy to Brazil nut is common, frequently has an onset in the first few years of life, generally persists, and accounts for severe and potentially fatal allergic reactions. The ubiquity of this food in the modern diet makes avoidance difficult, and accidental ingestions, with reactions, are common (1,31-36). Symptoms include vomiting, diarrhoea and other manifestations associated with food allergy: laryngeal oedema, atopic dermatitis, urticaria and anaphylaxis (1, 36-37).
The probability of patients with nut allergy having IgE antibodies to a particular combination of Peanut, Hazel nut and Brazil nut is similar, whatever the patients' age or sex. The apparent increase in multiple nut reactivity with increasing age may therefore be due to exposure of previously unchallenged sensitivity. The frequency of multiple-nut specificity is sufficiently high that patients should always be tested for allergy to a range of nuts if they have a history of reacting to any nut (38). In a study of 62 patients (adults and children) with nut allergy, Peanuts were the commonest cause of allergy (n=47), followed by Brazil nut (n=18), Almond (n=14), and Hazel nut (n=13) (35).
In an American study of 115 patients aged 4-19.5 years, 2% (n=1) were graded as mildly allergic to Brazil nut, and 4% (n=2) were graded as severely allergic. The study also concluded that around 9% of children with tree nut allergy outgrow their allergy. (39) An earlier American study by the Food Allergy and Anaphylaxis Network (FAAN) Peanut and Tree Nut Allergy Registry collected information on 5,149 patients (mainly children) and found that 34% were allergic to Walnut, followed by Cashew (20%), Almond (15%), Pecan (9%), and Pistachio (7%). Less than 5% each were allergic to Hazel, Brazil, Pine, Macadamia and Hickory nuts (40). It is evident that the frequency of reported allergy depends on the population group being studied and that in countries where the consumption of Brazil nut is low, the prevalence of reported allergy to this nut will be low.
A study reports on 11 patients with anaphylaxis after eating Brazil nuts and on 10 subjects with no symptoms to this food, although both groups had IgE antibodies to Brazil nut. A number of allergenic components with molecular weights ranging from 4 to 58 kDa were isolated. All sera from symptomatic patients recognised the Brazil nut 2S albumin, whereas the other allergens each bound IgE antibodies from less than 50% of sera. No sera from asymptomatic subjects showed IgE antibody binding to the 2S albumin, but sera did recognise 25 to 58 kDa components, which are minor allergens (5). Therefore, minor Brazil nut allergens were thought to result only in sensitisation to Brazil nut and not in allergic symptoms (5). However, this is contradicted by a study of a 15-year-old boy who experienced 2 distinct episodes of generalised urticaria about 30 minutes after eating Brazil nut. An IgE antibody test was very positive to Brazil nut. Serum IgE was positive to Brazil nut but negative to Mustard, Poppy seed, Sesame seed and Sunflower seed, suggesting no sensitisation to the 2S albumin allergen (2). The 2S albumins may be very important in food-induced anaphylaxis (6).
Anaphylaxis to Brazil nut has been reported. A British report from the Isle of Wight (population 125,000) described 12 cases of allergy to Brazil nut recorded over 8 years from 1983 to 1991. Eleven patients developed angioedema, 7 generalised urticaria, 5 bronchospasm, 2 stridor, 2 throat tightness, 2 itchy mouth and 1 syncope. Onset of symptoms was less than 1-3 minutes in all. Eight patients were shown to have significant skin reactivity for Brazil nut. In 6 out of 8 patients, Brazil nut IgE antobodies were demonstrated (> 0.7 kUA/l). In 3 patients there was no definite evidence of IgE-mediated hypersensitivity. Total IgE was normal in 5 patients with severe reactions. Ten out of 12 patients had other atopic diseases such as asthma, eczema or allergic rhinitis, usually from infancy or early childhood. Seven out of 8 patients were positive to several food and/or inhalant allergens on skin test (36).
Anaphylaxis to Brazil nut may occur even with no previous history of ingestion of this nut. This was reported from SPT investigation for Brazil nut sensitisation in a young adult who had experienced an adverse reaction presumed to be a result of allergy to Walnut. Immediately after the skin was pricked with fresh Brazil nut, an episode of severe anaphylaxis occurred, requiring epinephrine and intravenous steroids. The authors thought this might have resulted from cross-reactivity, as occurs with other tree nuts (41).
Anaphylaxis was also reported in a 31-year-old woman, known to have rhinoconjunctivitis and asthma, who developed pharyngeal itching, lip swelling, dysphonia, dyspnoea, wheezing, and generalised macular exanthema 10 minutes after eating a Brazil nut. She had previously developed oral allergy syndrome after eating Almond, Walnut, Sunflower seed, and Hazel nut. She had suffered from abdominal pain after eating Chestnut. She tolerated Peanut and Pistachio. Skin reactivity was detected for Brazil nut, Almond, Peanut, Chestnut, Sunflower seed, Pistachio, Hazel nut, Walnut, and Cashew nut. Serum IgE was raised for Almond, Peanut, Chestnut, Pistachio, Hazel nut and Sunflower seed. IgE antibody level to Brazil nut was 2.37 kUA/l (37).
Patients sensitised to minor Brazil nut allergens are reported to not have allergic symptoms (5), but this is contradicted by a report on a 15-year-old boy who experienced 2 distinct episodes of generalised urticaria about 30 minutes after eating Brazil nut. SPT and serum IgE was present for Brazil nut. As serum IgE was present for Brazil nut but not for Mustard, Poppy seed, Sesame seed or Sunflower seed, the authors concluded that no reactivity was therefore shown to 2S albumins, which suggests that a minor allergen was involved (2).
Food allergens have been reported to be present in breast milk. A study also reports on a 20-year-old woman with documented Brazil nut allergy who developed widespread urticaria and mild dyspnoea after intercourse with her boyfriend, who had earlier consumed Brazil nuts. SPT evaluation with the boyfriend's semen after Brazil nut consumption confirmed significant reactivity, whereas a sample before nut consumption was negative (42).
In a study to find the best approach to the diagnosis of Brazil nut allergy, 56 children and adults with a history of an allergic reaction to Brazil nut or other evidence of sensitisation were evaluated by questionnaire, SPT and serum IgE antibodies to Brazil nut, and by double-blind, placebo-controlled labial and, if necessary, oral challenges. The study concluded that a combination of history, SPT and IgE antibodies was adequate for achieving a diagnosis in the approximately 77% of patients with suspected Brazil nut allergy. However, a doubtful history combined with SPT result (between 1 and 5 mm), or a IgE antibody level less than 3.5 kUA/l, may require an oral challenge to help determine the risk of a Brazil nut allergic reaction (43).
Compiled by Dr Harris Steinman, email@example.com
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