Hazelnut (Corylus avellana)

Botanical Characteristics of Hazelnut (Corylus avellana)

• Scientific Name: Corylus avellana
• Family: Betulaceae (Birch family)
• Common Names: Hazelnut, Filbert nut, Cobnut
• Native Region: Europe and Western Asia

Tree and Fruit Description

• The hazelnut tree is a deciduous shrub or small tree, typically 3–8 meters tall.
• The nuts grow inside a hard shell, surrounded by a leafy husk.
• Hazelnuts are widely used in food products, especially in chocolates, spreads (Nutella), and baked goods.

Hazelnut as a Food Allergen

Hazelnuts are classified as a major food allergen by the U.S. FDA, requiring mandatory labeling.

Allergenic Proteins in Hazelnuts

Allergen Name	Protein Family	Molecular Weight (kDa)	Function	Cross-Reactivity
Cor a 1	PR-10 (Pathogenesis-Related)	~17 kDa	Defense protein	Cross-reactive with birch pollen (Bet v 1)
Cor a 8	Lipid Transfer Protein (LTP)	~9 kDa	Transport protein	Linked to peach, apple, cherry allergies
Cor a 9	11S Globulin (Legumin)	~40 kDa	Storage protein	Cross-reacts with walnuts, almonds, cashews
Cor a 11	7S Vicilin	~50 kDa	Seed storage protein	Cross-reacts with peanuts, soy, tree nuts
Cor a TLP (Cor a 2, Cor a 5, Cor a 6)	Thaumatin-like Proteins	~25 kDa	Defense proteins	May cross-react with fruits (banana, kiwi)

Epitope Mapping of Hazelnut Allergens

Hazelnut allergens contain linear and conformational epitopes that interact with IgE antibodies, leading to allergic reactions.

Cor a 1 (PR-10)

• Regions with IgE-binding epitopes:
  • Amino acids: 30–50, 100–120, 150–170
  • Core IgE-binding sites: Beta-strands and alpha-helix motifs
• Clinical Significance:
  • Mild allergen in most cases.
  • Strong cross-reactivity with birch pollen allergy (Bet v 1).
  • Causes Oral Allergy Syndrome (OAS).

Cor a 8 (LTP)

• Regions with IgE-binding epitopes:
  • Amino acids: 20–40, 70–90, 110–130
  • Core IgE-binding sites: Lipid-interacting domains
• Clinical Significance:
  • Highly stable allergen → causes systemic reactions and anaphylaxis.
  • Cross-reactive with peaches, apples, cherries (Rosaceae family).

Cor a 9 (11S Globulin)

• Regions with IgE-binding epitopes:
  • Amino acids: 50–70, 200–230, 280–310
  • Core IgE-binding sites: Hydrophobic beta-sheet regions
• Clinical Significance:
  • Major hazelnut storage protein.
  • Cross-reacts with walnuts, almonds, and cashews.
  • Heat-stable and digestion-resistant → severe allergic reactions.

Cor a 11 (7S Vicilin)

• Regions with IgE-binding epitopes:
  • Amino acids: 40–60, 120–150, 220–250
  • Core IgE-binding sites: Globular structure with immunodominant loops
• Clinical Significance:
  • Cross-reacts with peanuts, soy, and other tree nuts.
  • Found in baked goods, chocolates, and spreads.

Stability of Hazelnut Allergens

Allergen	Heat Stability	Gastric Stability	Processing Effect
Cor a 1 (PR-10)	Low	Low	Destroyed by cooking
Cor a 8 (LTP)	High	High	Resistant to digestion
Cor a 9 (11S Globulin)	High	High	Stable after roasting
Cor a 11 (7S Vicilin)	Medium	High	Can survive food processing

• Hazelnut allergens like Cor a 8 and Cor a 9 remain stable, meaning roasted hazelnuts can still cause allergic reactions.
• Cor a 1 is heat-sensitive, so cooking may reduce its allergenicity.

Cross-Reactivity of Hazelnuts

Cross-Reactive Source	Similar Hazelnut Epitope Regions	Common Symptoms
Birch Pollen (Bet v 1)	Cor a 1 (30–50)	Oral Allergy Syndrome (OAS)
Peaches, Apples, Cherries (LTPs)	Cor a 8 (20–40)	Systemic reactions
Walnuts, Almonds, Cashews	Cor a 9 (50–70)	Anaphylaxis risk
Peanuts, Soy (7S Vicilin)	Cor a 11 (120–150)	Cross-reactivity

Symptoms of Hazelnut Allergy

Reactions can range from mild to life-threatening.

Mild Symptoms (Oral Allergy Syndrome – OAS)

• Itchy mouth, lips, throat.
• Mild swelling of tongue.
• Occurs mostly in birch pollen allergy sufferers (due to Cor a 1).

Moderate to Severe Symptoms

• Hives, skin rash.
• Vomiting, nausea, diarrhea.
• Swelling of face, eyes (angioedema).
• Wheezing, difficulty breathing.

Severe Reactions (Anaphylaxis)   Epinephrine (EpiPen®) is required for anaphylaxis

• Drop in blood pressure (hypotension).
• Severe airway constriction (wheezing, asthma).
• Throat swelling (laryngeal edema).
• Cardiac arrest (in rare cases).

Diagnostic Testing for Hazelnut Allergy

Skin Prick Test (SPT)

• Detects IgE sensitivity to hazelnut extract.
• Positive test confirms sensitization but not severity.

Serum IgE Testing

• Measures IgE antibodies against Cor a 1, Cor a 8, Cor a 9.

Oral Food Challenge (OFC)

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

Management and Prevention

Avoidance Strategies

• Read labels carefully → Hazelnuts are found in chocolates, Nutella, baked goods.
• Beware of cross-contamination → Especially with walnuts, almonds, and peanuts.

Emergency Treatment

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

Immunotherapy

• Oral Immunotherapy (OIT) is being researched for hazelnut desensitization.

Conclusion

• Hazelnut allergens (Cor a 1, Cor a 8, Cor a 9) can cause mild to severe reactions.
• Cross-reactivity with birch pollen, tree nuts, and fruits is common.
• Heat and digestion stability vary, with LTP (Cor a 8) being the most stable.
• Strict avoidance and emergency preparedness are necessary.