Almond

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Code: f20
Latin name: Amygdalus communis
Source material: Shelled almonds
Family: Rosaceae
Common names: Almond, Sweet Almond, Bitter Almond

Synonymes: A. dulcis, Prunus amygdalus and P. dulcis

The fruit and seeds of several other plants are known as Almonds. The seeds of the African shrub Brabeium stellatifolium are known as African Almonds. Country Almonds is a name given to the fruit of the East Indian tree Terminalia Catappa. The fruit of Canarium commune is known as Java Almonds.

Allergen Exposure

Geographical distribution
The Almond is the fruit of a vigorous, deep-rooted deciduous small tree belonging to the Rose family, which grows best in areas with dry, warm summers. The plant is believed to be a native of northern Africa and the Middle East. It occurs wild in Sicily and Greece and is extensively cultivated in northern Africa, southern Europe, Australia and the warmer parts of the United States, particularly California.

The fruit is a drupe or kernel stone fruit, resembling the Peach in its general structural characteristics. It is, however, much smaller, measuring about 4 cm in length. As in the Peach, the outer portion of the fruit coat (sarcocarp) is fleshy, while the inner portion (endocarp or putamen) is hard and encloses the kernel or seed, to which the term Almond is commonly applied.

Almonds come in many varieties, but the 2 major, universally recognised ones are the Sweet (Prunus amygdalus var. dulcis) and the Bitter (Prunus amygdalus var. amara). They appear very similar but are different in chemistry. In the Bitter variety, substantial amounts of amygdalin (or "laetrile"), containing hydrocyanic (or "prussic") acid, are found. The Bitter almond is banned from retail sale in the US because of the toxicity of unprocessed amygdalin. Only Sweet almonds are readily edible.

Environment
Almonds have always been an important ingredient in Arabic dishes and Indian curries. Sweet almonds (fresh, blanched, roasted, candied, and smoked; whole, sliced, chopped, and in paste form) are readily available in markets and are used in a variety of recipes, especially for sweets and confectionery. Heat-processed Bitter almonds are used to flavour extracts, flavourings, liqueurs and syrups. The purified fixed oil from both varieties of Almonds has food uses, particularly as a condiment. Almonds are a nutritional powerhouse, packed with calcium, fibre, folic acid, magnesium, potassium, riboflavin and vitamin E.

Medicinally, externally applied Almond oil is an emollient; taken internally, a laxative, nutritional substitute and supplement (particularly in cases of diabetes), and a remedy for nervous system disorders such as whooping cough and spasmodic troubles.

Almond oil and paste often feature in cosmetics and toiletries.

Unexpected exposure
See under Environment.

Allergens
A number of allergens of various molecular weights have been isolated: 12, 30, 37, 45, 50, and 62 kDa proteins. Several of these proteins were shown to be similar to a 7S globulin and a 2S albumin (1-2). Two allergens isolated were reported to be major allergens - 1 heat-labile and the other heat-stable. The Almond major protein (AMP or amandin), the primary storage protein in Almonds, is the major allergen recognised by Almond-allergic patients and is probably the 2S albumin identified previously and shown to be a heat-stabile allergen (3). The antigenicity of processed Almond proteins has been shown to be very stable when compared with that of the unprocessed counterpart (4).

To date, the following allergens have been characterised:

  • Pru du 2S Albumin, a 2S albumin (1).
     
  • Pru du Conglutin, a conglutin (1).
     
  • Pru du LPT, a lipid transfer protein. (5-7).
     
  • Pru du Amandin, a 360 kDa hexameric protein, an 11S legumin-like protein (8-9).
     
  • Pru du 4, a profilin (10-12).
     
  • Pru du 5, an acid ribosomal protein P2 (11,13).

Amandin is a legumin-type protein and is composed of 2 major types of polypeptides, with estimated molecular weights of 42-46 and 20-22 kDa, linked via disulfide bonds. Amandin is not a glycoprotein (7).

Pru du 4, a profilin, is a minor allergen: 6 of 18 patient sera (33%) were shown to react with the recombinant Pru du 4 protein, and 8 of 18 (44%) reacted with the native Pru du 4. More than 1 native Almond profilin isoform was isolated (9).

Potential cross-reactivity

An extensive cross-reactivity among the different members of the family, and in particular of the genus, could be expected (14). Potential clinical allergy to other Rosaceae should not be overlooked. If the reported reaction is confirmed, current tolerance to other Rosaceae should be precisely established, unless there has been ingestion without symptoms after the reaction (15).

A major Almond allergen, a 2S albumin, can be expected to result in cross-reactions with other foods containing this protein, e.g., Walnut, Sunflower seed and Peanut (1,16-17). Ara h 2, a major Peanut allergen, is a conglutin /2S albumin. In a study evaluating serum from Peanut-allergic patients, Ara h 2 specific serum IgE antibodies bound to proteins present in Almond and Brazil nut extracts, indicating that Ara h 2 shares IgE-binding epitopes with Almond and Brazil nut allergens (18). The biological activity of cross-reactive IgE antibodies between Peanut, Brazil nut and Almond has been demonstrated (19).

The Lipid Transfer Proteins are major allergens of Rosaceae fruits and will result in varying degrees of cross-reactivity with other family members, as well as between Almond and non-family-related food containing LPT allergens (20-21). For example, Apricot LTP has a sequence identity of 91% and 94% with Peach and Almond LTPs, respectively. (22) Hazel nut LTP has a 62% amino acid homology with the LTP from Almond, 59% with Peach LTP and 59% with Cherry LTP. (5) Apricot LTP has a sequence identity of 91% and 94% with Peach and Almond LTP, respectively (7).

Pru du 4 is a profilin, and cross-reactivity between Almond profilin and other profilin-containing plants is possible (10). Almond and Ryegrass profilin were shown to be mutually inhibitable, so there must be cross-reactivity with grass pollen profilin (9). As profilin is susceptible to denaturation, variable reactivity will result (10).

The existence of common antigenic bands between Pine nut and Almond has been reported, and this may result in cross-reactivity between these foods (23-24).

In an in vitro study, Pru du Amandin has been reported to be cross-reactive with a minor 50 kDa protein of Maize (a gamma-zein), as well as having low cross-reactivity with the 27 kDa gamma-zein. The 50 kDa Maize gamma-zein also reacted with IgE from pooled human sera of patients with self-reported severe Almond allergy (25).

An association between pollen allergy and Almond allergy has been reported. Almost 33% of Birch pollen-allergic patients were reported to also be hypersensitive to Almond and Cherry (26-27). Among 120 patients with pollen allergy and 80 patients with pollen-associated food allergy (as evaluated by skin prick tests, IgE antibody determinations, and HLA genotyping), monovalent pollen allergy was observed in 57% of the pollinosis patients, but in only 15% of patients with food allergy. Hazel nut (71%), Almond (65%), Walnut (44%) and Apple (41%) were the most common food allergens and were frequently associated with allergy to Birch pollen allergy (28).

In a study of 61 patients with a documented history of IgE-mediated reactions to Grape or its products (wine, juice, and wine vinegar), 81.9% were co-sensitised to Apple, 70.5% to Peach, 47.5% to Cherry, 32.8% to Strawberry, 49.2% to Peanut, 42.6% to Walnut, 31.1% to Hazel nut, 26.2% to Almond, and 29.5% to Pistachio. Whether this was due to the presence of panallergens was not elucidated (29).

Clinical Experience

IgE-mediated reactions
Almond may frequently result in sensitisation (30) and may commonly induce symptoms of food allergy (7,11,23,31-36). In general, nut allergies are potentially life-threatening and uncommonly outgrown, and appear to be increasing in prevalence. In studies of patients with nut allergy (adults and children), Peanuts are usually found to be the commonest cause, followed by Brazil nut, Almond, and Hazelnut (37). Other reports have indicated that the most common tree nut allergies are to Walnut, Almond, and Pecan nut. Initial reactions are reported to usually occur at home and in children, at 5 years of age on average. Adverse effects result from a first exposure in 72% of cases. Eighty-nine percent of the reactions involved the skin (urticaria, angioedema), 52% the respiratory tract (wheezing, throat tightness, repetitive coughing, dyspnoea), and 32% the gastrointestinal tract (vomiting, diarrhoea). Two organ systems were affected in 31% of initial reactions, and all 3 in 21% of reactions. Approximately 1/3 of Peanut-allergic individuals will have a co-existing tree nut allergy.

In a retrospective study of 213 Australian children with Peanut or tree nut allergy, 177 patients (83.1%) had Peanut allergy, 27 (12.6%) had Cashew allergy, and 9 had allergy to other tree nuts (4.2%; 2 each to Almond and Pecan, 1 each to Hazel nut and Walnut, and 3 to a mixture of nuts) (38). A cross-sectional, descriptive, questionnaire-based survey conducted in schools in Toulouse, France, found that of 2,716 questionnaires returned, 192 reported a food allergy. Tree nut allergy was self-reported in 19 (7.8%), with 10 for Hazel nut, 6 for Walnut, 2 for Almond and 1 to Cashew. (39) In an American study of 115 patients aged 4-19.5 years, 37% reported an allergy to 1 or more Tree nuts; 19% reported mild adverse reactions to Almond, and 1 patient experienced severe adverse effects (40). An earlier study, by the Food Allergy and Anaphylaxis Network (FAAN) Peanut and Tree Nut Allergy Registry in the USA, collected data on 5,149 patients (mainly children) and reported Walnut as the first cause of allergic reactions to Tree nuts in 34%, followed by Cashew (20%), Almond (15%), Pecan (9%), and Pistachio (7%) (41).

Accidental ingestion occurs frequently outside of the home. As rather low levels of Almond proteins can provoke an allergic reaction in sensitised individuals, these reactions often require emergency treatment (42). Kiss-induced allergy, a form of allergy by proxy, may occur with Almond, and symptoms may be local or general, mild, moderate or severe. A careful history will determine that the symptoms appeared within minutes after a kiss, the time between eating the allergen and the kiss being quite variable, from a few minutes up to 2 hours (43).

Even traces of residual Almond protein in Almond nut oil may pose a threat to patients with allergy, depending on the method of manufacture and processing (44). Anaphylaxis may thus be a common presenting complaint (1,45). An Italian study describes 5 patients with Almond allergy, who were shown to have skin reactivity for Almond. Four patients experienced oral allergy symptoms and anaphylaxis, whereas 1 only experienced oral allergy syndrome, with itching of the oral cavity and rhino-conjunctivitis (1).

A review was done of 601 patients aged 1 to 79 years of age who had experienced anaphylaxis. Of the 133 food reactions, Peanut was responsible in 25, tree nuts in 13, and Almond or Peach in 5 (46).

The sudden and unexpected death of an individual following the ingestion of Hazel nuts and Almonds, to which the individual had not been previously known to be allergic, was described. After eating a dessert containing these nuts, he experienced symptoms of his throat closing and swelling of his lips. He had previously experienced similar symptoms after ingesting Peanuts but had thought nothing of it after being assured that no contact with Peanut was possible. He suddenly collapsed during vigorous dancing. The death was not associated with cutaneous or laryngeal manifestations of anaphylaxis (47).

Other cutaneous symptoms described include acne vulgaris (48) and atopic dermatitis (49). A 5-month-old child with atopic dermatitis developed contact dermatitis to Almond. Persistent eczema correlated with the application of Almond oil on the cheeks and buttocks. The child had not ingested Almond, and her mother did not report Almond intake during her breast-feeding. IgE antobodies to Almond was detectable. Sensitisation appeared to occur from a percutaneous route.

Asthma may occasionally be associated with Almond. In the evaluation of 163 food-allergic asthmatic children for food-induced asthma, using DBPCFC, 1.5% of the group demonstrated Almond as a culprit (25).

Other reactions
Cyanide poisoning after Bitter almond (Prunus amygdalus var. amara) ingestion has been reported (50).

Compiled by Dr Harris Steinman, harris@zingsolutions.com

References

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