Almond (Prunus dulcis) – Botanical, Allergenic, and Nutritional Overview

Botanical Characteristics

• Scientific Name: Prunus dulcis
• Family: Rosaceae (Rose family)
• Common Names: Almond, Sweet Almond
• Origin: Native to the Middle East and South Asia, now widely cultivated in California, Spain, and Italy.

Tree and Fruit Description:

• The almond tree is a small deciduous tree, typically 4–10 meters in height.
• It produces drupe fruits, where the edible almond seed is encased in a hard shell.
• Flowers are white to pale pink and bloom in early spring.
• The outer hull splits open when mature, revealing the hard-shelled almond inside.

Almond as a Food Allergen

The U.S. FDA classifies almonds as a major food allergen, requiring clear labeling on food products.

Allergenic Proteins in Almonds:

• Pru du 6 (11S globulin)
• Pru du 3 (Lipid Transfer Protein – LTP)
• Pru du 4 (Profilin protein)

Symptoms of Almond Allergy:

• Mild Reactions: Itching, swelling of lips, hives, nausea.
• Severe Reactions: Wheezing, vomiting, anaphylaxis (in extreme cases).
• Cross-Reactivity: Almonds share allergenic proteins with other tree nuts, particularly walnuts, hazelnuts, and cashews.

Nutritional Value of Almonds (Per 100g Raw Almonds)

• Calories: ~579 kcal
• Protein: ~21g
• Fat: ~50g (mainly monounsaturated fats)
• Carbohydrates: ~22g (including ~12g fiber)
• Vitamins & Minerals:
  • High in Vitamin E (~25mg, 170% DV) → Antioxidant properties.
  • Rich in Magnesium (~268mg, 67% DV) → Supports muscle and nerve function.
  • Good source of Calcium, Iron, and Zinc.

Uses of Almonds

• Food Products
  • Consumed raw, roasted, or blanched.
  • Used in almond butter, almond milk, marzipan, and baked goods.
  • Almond flour is popular in gluten-free and low-carb diets.
• Cosmetic & Health Uses:
  • Almond oil is used in skin and hair care due to its moisturizing properties.
  • Extracts are found in soaps, lotions, and massage oils.
• Industrial Uses:
  • Almond shells are used for animal feed and biofuel.

Summary

Almond (Prunus dulcis) is a nutritionally rich tree nut with widespread culinary and industrial applications. However, it is a significant food allergen due to its stable allergenic proteins, which can trigger mild to severe immune responses. Its versatility makes it a staple in diets, skincare, and health products, but individuals with nut allergies must avoid it.

Molecular Analysis of Almond (Prunus dulcis) Allergenic Proteins

Almonds contain multiple allergenic proteins that can trigger IgE-mediated immune responses in susceptible individuals. Below is a detailed molecular breakdown of these proteins, including their structure, function, and cross-reactivity.

Allergen Name	Protein Family	Molecular Weight (kDa)	Function	Cross-Reactivity
Pru du 6	11S Globulin (Legumin)	~360 kDa (hexamer)	Storage protein	Common in tree nuts (e.g., walnut, cashew, hazelnut)
Pru du 3	Nonspecific Lipid Transfer Protein (nsLTP)	~9 kDa	Defense against pathogens	Cross-reacts with peach, apple, and other Rosaceae fruits
Pru du 4	Profilin	~15 kDa	Cytoskeletal protein	Cross-reacts with grass and birch pollen
Pru du 5	2S Albumin	~5-9 kDa	Seed storage protein	Common in peanuts and tree nuts
Pru du 8	Bet v 1 Homolog	~17 kDa	Defense protein	Linked to birch pollen allergy

Structural and Functional Aspects of Major Almond Allergens

Pru du 6 (11S Globulin – Legumin)

• Structure:
  • Hexameric protein with subunits (~60 kDa each) forming a compact globular structure.
  • Stable against heat and digestion, making it a strong allergen.
• Clinical Significance:
  • Major cause of severe allergic reactions.
  • Highly cross-reactive with other tree nuts (walnuts, pecans, cashews).
• Immunogenicity:
  • Contains multiple IgE-binding epitopes.

Pru du 3 (Lipid Transfer Protein – LTP)

• Structure:
  • Small, compact, and disulfide-bond stabilized, making it resistant to heat and enzymatic digestion.
• Clinical Significance:
  • Linked to oral allergy syndrome (OAS) and systemic anaphylaxis.
• Cross-Reactivity:
  • Found in peach, apple, cherry, and plum, which belong to the Rosaceae family.
  • Highly stable, making even cooked almond-containing foods allergenic.

Pru du 4 (Profilin)

• Structure:
  • Small cytoskeletal protein involved in actin polymerization.
• Clinical Significance:
  • Often associated with mild allergic reactions like itchy mouth (OAS).
• Cross-Reactivity:
  • Similar to Birch pollen (Bet v 2), leading to pollen-food syndrome.

Pru du 5 (2S Albumin)

• Structure:
  • Small seed storage protein with a high cysteine content, making it resistant to heat and gastric digestion.
• Clinical Significance:
  • Associated with severe allergic reactions.
• Cross-Reactivity:
  • Found in peanuts, walnuts, and Brazil nuts.

Pru du 8 (Bet v 1 Homolog)

• Structure:
  • Homologous to Bet v 1 (Major Birch Pollen Allergen).
• Clinical Significance:
  • Triggers pollen-associated food allergy syndrome.
• Cross-Reactivity:
  • Strong reaction with birch pollen allergy sufferers.

Heat and Digestive Stability of Almond Allergens

• Heat Resistance:
  • Pru du 3, Pru du 6, and Pru du 5 are highly stable to heat, meaning roasted or processed almonds still retain allergenicity.
• Gastric Stability:
  • Pru du 6 and Pru du 5 resist breakdown in the stomach, increasing the likelihood of systemic allergic reactions.
• Processing Effects:
  • Blanching, roasting, and grinding do not eliminate allergenicity.
  • Almond extracts in food products (e.g., almond milk, marzipan) can still trigger allergic responses.

Diagnostic Testing for Almond Allergy

Skin Prick Test (SPT)

• Measures immediate IgE reaction to almond extract.
• Positive test indicates sensitization but does not confirm clinical allergy.

Serum Specific IgE Test

• Blood test measuring IgE antibodies against almond proteins.
• Higher IgE levels = Greater allergy risk.

Oral Food Challenge (OFC)

• Gold standard for diagnosis.
• Administered in a controlled medical setting to confirm allergy.

Managing Almond Allergy

Avoidance Strategies

• Read Labels: Almonds are present in many baked goods, cereals, chocolates, and plant-based milk products.
• Cross-Contamination Risks: Often processed alongside walnuts, pecans, and peanuts.

Treatment Options

• Epinephrine Auto-Injector (EpiPen®): First-line treatment for anaphylaxis.
• Antihistamines: Useful for mild reactions (itching, hives).
• Immunotherapy (OIT): Experimental treatments aim to desensitize patients.

Cross-Reactivity of Almonds with Other Allergens

Allergen Source	Cross-Reactive Almond Protein	Common Symptoms
Walnut, Hazelnut, Cashew, Brazil Nut	Pru du 6 (11S Globulin)	Systemic allergic reactions
Peach, Apple, Cherry, Plum	Pru du 3 (LTP)	Oral Allergy Syndrome (OAS)
Birch Pollen (Bet v 1, Bet v 2)	Pru du 8 (Bet v 1 Homolog), Pru du 4 (Profilin)	Mild itching, throat irritation

Conclusion

• Almond allergy is triggered by multiple IgE-binding proteins, with Pru du 6 (11S globulin) and Pru du 3 (LTP) being the most clinically significant.
• Almond allergens are heat-stable, digestion-resistant, and cross-reactive with other tree nuts, pollen, and stone fruits.
• Diagnosis requires IgE testing and/or an oral food challenge.
• Management involves strict avoidance and emergency preparedness with epinephrine.