What kind of protein is present in peanuts? A comprehensive look at arachin, conarachin, and allergens

January 4, 2026 •

4 min read

Did you know peanuts are a powerhouse of plant-based protein, with approximately 25.8 grams per 100 grams, a higher concentration than many true nuts? We delve into the specifics of what kind of protein is present in peanuts, identifying the major types and their health implications.

Quick Summary

Peanut protein is primarily composed of globulin storage proteins, arachin (11S) and conarachin (7S and 2S), along with other allergenic compounds known as Ara h proteins that are crucial for understanding potential allergy risks and nutritional value.

Key Points

Major Protein Types: Peanuts primarily contain globulin storage proteins, arachin (an 11S globulin) and conarachin (a 7S globulin and 2S albumin).
Allergenic Potential: Specific allergenic proteins, known as Ara h proteins (Ara h 1 through Ara h 13), are responsible for triggering allergic reactions in sensitized individuals.
Amino Acid Profile: Peanut protein provides all 20 amino acids, though it is a low source of methionine, which is often balanced in a varied plant-based diet.
High Digestibility: The protein in peanuts is highly digestible, comparable to some animal protein sources, enhancing its nutritional accessibility.
Processing Effects: Heat treatments like roasting can modify protein structure, potentially increasing the allergenicity of proteins like Ara h 2 and Ara h 6.
Beyond Protein: Peanuts offer many other nutrients, including beneficial unsaturated fats, fiber, and various vitamins and minerals.

The Major Protein Families in Peanuts

Peanuts (Arachis hypogaea), botanically legumes, contain a complex mix of proteins. The two most abundant protein families are globulins, specifically named arachin and conarachin. These storage proteins are critical for the plant's growth and development, but also serve as the primary source of protein for consumers. These proteins can be further broken down into specific classes based on their structure and function.

Arachin: The 11S Globulin Family

Arachin represents the largest fraction of peanut proteins and belongs to the 11S globulin family, also known as legumins. These proteins form hexameric structures, and are post-translationally cleaved into smaller acidic and basic subunits.

Ara h 3: This is the major allergenic isoform within the arachin group. It is heat-stable and resistant to digestion, making it a persistent allergen. It is responsible for triggering severe reactions in a significant portion of the peanut-allergic population.
Ara h 4: Originally considered a distinct allergen, Ara h 4 is now recognized as an isoform of Ara h 3.

Conarachin: The 7S and 2S Globulin Families

Conarachin is the second most prevalent group of proteins in peanuts and contains both 7S vicilins and 2S albumins.

Ara h 1: This glycoprotein is a 7S vicilin that forms a trimer structure under normal conditions. It is a major peanut allergen, with IgE antibodies recognizing both its native structure and denatured monomers.
Ara h 2 and Ara h 6: These are 2S albumins and potent allergens. Ara h 2 is considered one of the most critical peanut allergens due to its high prevalence of IgE binding and heat stability. Ara h 6 is highly similar to Ara h 2 and possesses similar allergenic activity.
Ara h 7: Also a 2S albumin, Ara h 7 is another conglutin-type protein with allergenic properties.

The Role of Peanut Proteins in Allergies

Peanut allergy is a serious and potentially life-threatening condition mediated by the immune system's reaction to specific peanut proteins. The proteins listed above, particularly Ara h 1, Ara h 2, Ara h 3, and Ara h 6, are major allergens responsible for most allergic reactions. The identification of these specific proteins allows for component-resolved diagnostics (CRD) to better understand individual sensitization patterns. Roasting and other processing methods can alter the structure of these proteins, which may affect their allergenic potential for some individuals.

Beyond the Major Allergens

In addition to the main storage proteins, other minor allergens exist in peanuts, each with distinct characteristics:

Ara h 5: A profilin protein that regulates cellular processes.
Ara h 8: A Bet v 1-related protein, often associated with cross-reactivity to birch pollen allergens.
Ara h 9: A lipid-transfer protein (LTP) with regional allergenic significance, particularly in Mediterranean areas.
Ara h 10 and Ara h 11: Oleosin proteins involved in structural stability.
Ara h 12 and Ara h 13: Defensin proteins, part of the plant's defense system.

Nutritional Quality and Amino Acid Profile

Peanut protein is recognized for its high nutritional quality, containing all 20 amino acids in varying proportions. While considered a high-quality plant-based protein comparable to meat and eggs for human health and growth, it is not a 'complete' protein in the strictest sense because its levels of methionine are relatively low. However, this is easily compensated for in a balanced diet by consuming other plant-based proteins throughout the day. Peanuts are particularly rich in the amino acid arginine, which offers various health benefits, including supporting cardiovascular function. The protein digestibility of peanuts is also very high, further contributing to their nutritional value.

Protein Composition Comparison: Peanuts vs. Other Plant Sources


Feature	Peanuts	Soybeans	Almonds	Whole Wheat
Protein Content (per 100g raw)	~25.8 g	~36 g	~21 g	~13 g
Key Protein Families	Globulins (Arachin, Conarachin)	Glycinin, Conglycinin	Storage Proteins, Albumins	Gluten, Gliadin, Glutenin
Limiting Amino Acid	Methionine	Methionine, Cysteine	Lysine	Lysine, Threonine
Protein Digestibility Score (PDCAAS)	~0.70	~0.91	N/A	~0.46
Allergenic Potential	High (Ara h proteins)	Moderate (Gly m proteins)	Moderate (Cor a proteins)	Low (Tri a proteins)

Conclusion

In summary, the protein content in peanuts is more complex than a simple glance might suggest. Beyond their impressive quantity and overall high nutritional quality, the specific proteins like arachin, conarachin, and the various Ara h allergens are vital to understanding their full impact on human health. While they are a valuable source of plant-based protein and essential amino acids for most, for those with allergies, these specific protein structures pose a significant health risk. The distinct composition of these proteins also influences factors like digestibility and potential cross-reactivity with other plant foods. Ongoing research into these proteins continues to improve diagnostics and may someday lead to hypoallergenic peanut varieties. For a comprehensive overview, refer to studies like the "Functional Uses of Peanut (Arachis hypogaea L.) Seed Storage Proteins" in the IntechOpen journal.

Note: The content provided is for informational purposes. Individuals with food allergies should consult with a healthcare professional before consuming peanuts or peanut products.

Frequently Asked Questions

The two primary storage proteins in peanuts are arachin and conarachin, which belong to the globulin family and are essential for the plant's growth.

Peanuts contain all 20 amino acids but are low in methionine. While not a 'complete' protein on its own, its amino acid profile is comparable to animal sources for human health and complements other dietary proteins.

Ara h proteins are the specific proteins in peanuts (e.g., Ara h 1, 2, 3) identified as allergens by the International Union of Immunological Societies. They are important because they trigger allergic responses in individuals with peanut allergy.

Roasting can cause non-enzymatic modifications, like the Maillard reaction, which can alter the protein structure. This process can sometimes increase the allergenic properties of certain proteins, such as Ara h 2 and Ara h 6.

No, peanut proteins are generally highly digestible. Studies indicate that their digestibility is comparable to that of animal proteins, making their nutrients readily available to the body.

No, the specific proteins that trigger an allergic response can vary between individuals. Some may react strongly to Ara h 1, while others have a more potent reaction to Ara h 2 or another Ara h protein.

The protein content per gram is slightly higher in roasted peanuts than in boiled peanuts, primarily due to the lower water content in the roasted variety. The fundamental protein types remain the same, although heat exposure can alter their structure.