Latin name: Macadamia spp.
Source material: Shelled nuts
Common names: Macadamia nut, Queensland nut, Australian nut
Macadamia nuts are the fruit of an Australian tropical evergreen tree, and are also known as Queensland or Australian nut. The tree was exported to Hawaii in the 1890's as a source of shade but subsequently became a crop. It is also grown in warm Mediterranean areas, in the southern USA and in South Africa. The seed grows on 2 species of trees (M. tetraphylla and M. intergrifolia). The commercial Macadamia tree (M. intergrifolia) grows more than 12 m tall and has creamy-white flowers.
The "nut" is not truly a nut but a seed (1). The round, whitish kernel is enclosed in an extremely hard, brown shell, about 2.5 cm in diameter and 2 to 3 mm thick. The shell is in turn contained in a fibrous green husk.
Australia is the world's largest producer of the nut. For 7 months of the year the nuts fall on their own and are harvested from the ground by hand and taken to the factory for processing. Workers ("nut sorters") stand beside the "shell" conveyer and pick out by hand salvageable nut kernels that have escaped the mechanical separators. The importance of this process for allergy consists in both the intense occupational exposure and the relative rarity and costliness of the nuts. The kernels are then dry- or oil-roasted (2).
The nuts are richly flavoured and high in protein. Their oil content (70%) is higher than that of other nuts.
Macadamias can be consumed fresh or roasted and are added to a variety of foods, including snack bars, cereals, and nut mixes. Ground Macadamia meal is becoming an increasingly popular ingredient in baked goods, as is cold pressed Macadamia oil (3).
No allergens from this plant have yet been characterised.
A 17.4 kDa protein appears to be the major allergen and is present in raw and roasted extracts (4).
A vicillin with anti-bacterial properties has been isolated, but its allergenicity was not determined (5).
Macadamia nut belongs to the Proteaceae family, which are classified separately from most other tree nuts and from Peanuts.
Partial cross-reactivity has been reported between Hazel nut and Macadamia nut (4). In a study of Almond, antibodies developed to Almond were shown to be specific for Almond; however, some cross-reactivity was observed with extracts of some tree nuts and of Sesame seeds. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and Western immunoblotting indicated that anti-Almond antibodies recognised proteins extracted from Black walnuts, Brazil nuts, Cashews, Hazel nuts, Macadamia nuts, Pistachios, and Sesame seeds, in addition to those from Almond (6).
Macadamia nut, although not as common a food as many other tree nuts, may occasionally cause serious allergic reactions in sensitised individuals. Cases are perhaps becoming more frequent because of the increasing use of Macadamia nuts, alone and in other products (7-8). In particular, Macadamia nut is becoming more frequently available in nut mixes and is being sold in countries which did not previously import it.
In an American study of 115 patients aged 4-19.5 years, moderately severe reactions to Macadamia were reported in 3 (13%) individuals, and severe reactions in 2 (4%) (9). In a telephonic survey, of 118 subjects reporting an allergy to Peanut or tree nut, 2 self-reported allergy to Macadamia nut (10).
Macadamia nut-induced uvular angioedema, angioedema of the posterior part of the tongue, dysphagia, chest tightness, chest pain, and chest pruritis were described in a 36-year-old man. Symptoms occurred 5 minutes after eating a single chocolate-covered Macadamia nut. A prick to prick test with fresh Macadamia nut was positive (11).
A study reported on 2 patients with allergy to Macadamia nut. A 48-year-old woman reported oral allergy symptoms occurring within 10 minutes of ingestion of 6-8 Macadamia nuts, followed by palpitations, dyspnoea, dizziness, flushing and severe itch. Skin reactivity was detected. A 34-year-old man presented with tongue swelling, itchy, hot palms, swollen hands and throat tightness, which developed within minutes after eating a single Macadamia nut. SPT was positive (3).
Reactions may be severe and result in anaphylaxis (8,12). An 18-year-old woman had immediate oral itching when eating flourless orange cake made with Macadamia meal. Within 5 minutes, this reaction had progressed to anaphylaxis (4). Anaphylaxis following contact with Macadamia nut has been reported in an infant (13).
A 42-year-old man developed generalised pruritus, itching of the throat, rhinitis, dyspnoea and dizziness 5 minutes after eating a few roasted Macadamia nuts. Skin prick tests were positive to Hazel nut and roasted Macadamia nut but negative to Peanut, Almond, Brazil nut and Walnut. A 34-year-old man repeatedly developed severe oral burning, itching and swelling after eating Hazel nut, Walnut, Brazil nut, Almond and Macadamia nut, but tolerating Peanut and Cashew nut. SPT was positive to Peanut, Almond, Hazel nut, Brazil nut and Walnut but negative to Cashew nut. A prick-to-prick IgE determination was positive for Macadamia nut (14).
A 23-year-old female with a history of atopic dermatitis, allergic rhinitis, and allergic conjunctivitis reported that in her fourth year of primary school, she ate Macadamia nuts and developed oral discomfort and generalised urticaria. In her second year of junior high school, she ate Macadamia nuts and developed oral and pharyngeal discomfort, followed by generalised urticaria and dyspnoea. At the age of 20 years, she also developed oral discomfort after eating vegetables in a Chinese dish containing Macadamia nuts. SPT using Macadamia oil extract was positive. Although she developed oral allergy syndrome after eating Macadamia nuts, she was negative for Bet v 1 and Bet v 2 as allergens (15).
Nut oils may pose a threat to patients with allergy, depending on the method of processing. IgE reactivity to proteins in Macadamia oil has been reported, based in testing of sera from patients with Macadamia allergy (16).
Occupational dermatitis from Macadamia nut shells was described in 15 nut sorters at a Macadamia nut processing plant. The nature of the allergen was not found but was thought to be confined to the shell, as opposed to the plant leaf or kernal (2).
Compiled by Dr Harris Steinman, email@example.com
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