Macadamia Nut – Macadamia integrifolia, Macadamia tetraphylla (Proteaceae)

Botanical Characteristics of Macadamia Nut

• Scientific Names:
  • Macadamia integrifolia (Smooth-shelled macadamia)
  • Macadamia tetraphylla (Rough-shelled macadamia)
• Family: Proteaceae
• Common Names: Macadamia nut, Queensland nut
• Native Region: Australia (now cultivated in Hawaii, South Africa, and Latin America)

Tree and Fruit Description

• Macadamia trees are evergreen, growing 6–12 meters tall.
• The nut is encased in a hard shell inside a green husk.
• Macadamia nuts are high in monounsaturated fats and commonly used in confections, nut butters, and cooking oils.

Macadamia Nut as a Food Allergen

Unlike other FDA-listed major tree nuts, macadamia nuts have a lower prevalence of allergic reactions. However, documented cases suggest IgE-mediated hypersensitivity in some individuals.

Allergenic Proteins in Macadamia Nuts

Allergen Name	Protein Family	Molecular Weight (kDa)	Function	Cross-Reactivity
Mac i 1	11S Globulin (Legumin)	~40 kDa	Storage protein	Common in tree nuts (walnut, pecan)
Mac i 2	7S Vicilin	~50 kDa	Storage protein	Cross-reacts with peanuts, almonds
Mac i 3	2S Albumin	~9 kDa	Seed storage protein	Found in cashews, Brazil nuts
Mac i LTP	Lipid Transfer Protein (LTP)	~9 kDa	Transport protein	Linked to peach, apple, cherry allergies

Cross-Reactivity

• Structurally similar to walnuts, pecans, and almonds.
• Mac i LTP may cross-react with Rosaceae fruits (peaches, apples, cherries).
• No significant cross-reactivity with peanuts or soy.

Epitope Mapping of Macadamia Allergens

Macadamia allergens contain linear and conformational IgE-binding epitopes.

Mac i 1 (11S Globulin – Legumin)

• Regions with IgE-binding epitopes:
  • Amino acids: 50–70, 120–140, 200–220
  • Core IgE-binding sites: Beta-sheet hydrophobic domains
• Clinical Significance:
  • Heat-stable, resistant to digestion.
  • Cross-reacts with walnuts, pecans, and hazelnuts.

Mac i 2 (7S Vicilin)

• Regions with IgE-binding epitopes:
  • Amino acids: 30–50, 100–120, 170–190
  • Core IgE-binding sites: Beta-barrel structures
• Clinical Significance:
  • Common storage protein allergen in tree nuts.
  • Similar to peanut (Ara h 1) and almond proteins.
  • Moderate resistance to digestion.

Mac i 3 (2S Albumin)

• Regions with IgE-binding epitopes:
  • Amino acids: 10–30, 90–110, 140–160
  • Core IgE-binding sites: Cysteine-stabilized domains
• Clinical Significance:
  • Highly stable allergen, causing severe allergic reactions.
  • Cross-reacts with cashews, Brazil nuts.
  • Resistant to heat and enzymatic breakdown.

Mac i LTP (Lipid Transfer Protein)

• Regions with IgE-binding epitopes:
  • Amino acids: 20–40, 80–100, 130–150
  • Core IgE-binding sites: Hydrophobic lipid-binding regions
• Clinical Significance:
  • May trigger systemic anaphylaxis in LTP-sensitive individuals.
  • Cross-reacts with Rosaceae fruits (peach, apple, cherry).

Stability of Macadamia Allergens

Allergen	Heat Stability	Gastric Stability	Processing Effect
Mac i 1 (11S Globulin)	High	High	Resistant to roasting
Mac i 2 (7S Vicilin)	Medium	Medium	Partially degraded
Mac i 3 (2S Albumin)	High	High	Survives processing
Mac i LTP	High	High	Stable even in refined nut oils

• Mac i 3 and Mac i LTP remain stable, meaning roasted macadamia nuts can still cause reactions.
• Processing (grinding, baking) may reduce Mac i 2 allergenicity.

Symptoms of Macadamia Nut Allergy

Reactions range from mild to life-threatening.

Mild Symptoms

• Oral Allergy Syndrome (OAS): Itchy mouth, tingling lips.
• Hives, skin rash.
• Nausea, vomiting, diarrhea.

Severe Symptoms (Anaphylaxis)   Epinephrine (EpiPen®) is required for anaphylaxis.

• Swelling of throat (laryngeal edema).
• Difficulty breathing, wheezing.
• Drop in blood pressure (anaphylactic shock).

Diagnosis and Testing

Skin Prick Test (SPT)

• Detects IgE-mediated reactions to macadamia extract.

Serum IgE Testing

• Measures IgE antibodies against Mac i 1, Mac i 2, Mac i 3.

Oral Food Challenge (OFC)

• Gold standard for confirming allergy.
• Performed under medical supervision.

Management and Prevention

Avoidance Strategies

• Read labels → Macadamia nuts are in chocolates, baked goods, nut butters.
• Cross-contamination risks → Often processed with walnuts, almonds.

Emergency Treatment

• Epinephrine Auto-Injector (EpiPen®).
• Antihistamines for mild reactions.
• Corticosteroids for prolonged symptoms.

Immunotherapy

• Oral Immunotherapy (OIT) is being studied for macadamia allergy desensitization.

Comparison with Other Tree Nuts

Nut	Major Allergen	Cross-Reactivity	Stability	Anaphylaxis Risk
Macadamia	Mac i 1, Mac i 2, Mac i 3	Walnuts, Pecans, Rosaceae fruits	High	Moderate
Walnut	Jug r 1, Jug r 2, Jug r 3	Pecans, Almonds, Peanuts	High	High
Hazelnut	Cor a 1, Cor a 9, Cor a 11	Birch Pollen, Tree Nuts	Moderate	Moderate
Pecan	Car i 1, Car i 2, Car i 3	Walnuts, Cashews	High	High

• Macadamia nuts are less allergenic than walnuts or pecans but can still cause severe reactions.
• Mac i LTP makes macadamia nuts cross-reactive with Rosaceae fruits.

Conclusion

• Macadamia nuts contain allergens (Mac i 1, Mac i 2, Mac i 3, Mac i LTP) that can trigger IgE-mediated reactions.
• Cross-reactivity exists with tree nuts (walnuts, pecans) and Rosaceae fruits.
• Roasting does not eliminate allergenicity.
• Severe reactions require epinephrine preparedness.