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f20 Almond

Almond
Code f20
Family Rosaceae
Genus Prunus
Species Prunus amygdalus
Route of Exposure Ingestion
Source Material Shelled almonds
Latin Name Amygdalus communis
Other Names Sweet Almond, Bitter Almond
Categories Food Of Plant Origin, Seeds & Nuts

Summary

Almonds are one of the most important nut species belonging to Rosaceae family. Sweet almonds (Prunus amygdalus dulcis) and bitter almonds (Prunus amygdalus amara) are the two main varieties of almonds. Various studies reported almonds as one of the most common allergens in the United States, Korea and the United Kingdom. Almond allergy may lead to oral allergy syndrome, allergic rhinitis, asthma, and atopic dermatitis. Pollen-food syndrome rarely causes anaphylaxis and mainly mild symptoms. Almond sensitized individuals should avoid direct or indirect consumption of almond. Cross-reactivity generally occurs with peach allergens, tree nut allergens as well as birch pollen allergens. Also, almond allergic patients are highly prone to cross-reactivity with mahleb. Almond sensitized people should avoid any intentional or un-intentional consumption of almond.

Allergen

Nature

Almond contains the highest levels of tocopherols amongst all nuts and is one of the most important nut species worldwide. (1). The almond tree is small and sheds it leaves annually. It increases to a height of 400-1000 cm and has a 30 cm diameter trunk. The young green twigs turn purplish on sunlight exposure and grey in the second year. The leaves are long up to 7.62 to 12.7 cm with serrated margins and petioles up to 2.5 cm The flowers have five petals of pale pink color having a diameter of 3-5 cm; produced singly or in pairs (2). Almond tree fruit is a drupe, has a fleshy hull covered by a hard shell, protecting the edible seed or kernel (3).

Habitat

Almonds are adapted to the Mediterranean climate. It can grow in mild winters and dry, hot summers. This variation leads to early budding and fast early shoot growth. It can develop a deep and extensive root system and can very well tolerate summer drought and heat (1). The almond tree matures in the third year and bears an economic crop till five to six years of maturity (2). 

Taxonomy

Almond belongs to the Rosaceae family (4). Three varieties of almonds are available that produce nuts, but only some are edible. A sweet almond variety is the one which is consumed, bitter almonds that are poisonous, and a mixture of bitter and sweet nuts. The two major cultivars of almonds are sweet almonds (Prunus amygdalus dulcis) and bitter almonds (Prunus Amygdalus amara) (2). 

Taxonomic tree of Almond  (5)  
Domain Eukaryota
Kingdom Plantae
Phylum Spermatophyta
Subphylum Angiospermae
Class Dicotyledonae 
Order Rosales
Family Rosaceae
Genus Prunus
Species Prunus dulcis


Tissue

Almonds contain about 50% lipids, 25% proteins and 20% carbohydrates. It has very low moisture content and varied minor bioactive compounds. It is also rich in fat (monounsaturated fatty acids and polyunsaturated fatty acids), vitamins (vitamin E, vitamin B), minerals (copper, calcium, magnesium, etc.) and various bioactive compounds (phytosterols, polyphenols) (6).

Epidemiology

Worldwide distribution

Almond allergy ranks fourth among the prevalence of tree nut allergies (7). Almonds are the third most common tree nut to cause allergy in the United States (8). About 9%–15% of pre-sensitized tree nut individuals reported almond allergy in the United States (4).

An investigational study conducted on 134 Korean patients having food allergies reported sensitization to almond in 11.2% of participants. About 16.3% belonged to the age group of 19-29 years, 13% to 40-49 years and 9.1% to 50-59 years. Almond sensitization was found to be higher in males (13.5%) than females (9.8%) (9).

The most common tree nut allergy in pre-sensitized people of the United Kingdom is almond (22% to 33%) (4, 10). A cross-sectional study reported the lower prevalence of almond allergy in Libyan children than the percentage in the general UK control population (11).

A study conducted in Mexico City reported a higher rate (43%) of almond sensitization in older children (6-17 years) (sIgE ≥0.1kUA/L) (12).

A cross-sectional questionnaire study, based on 1042 responses obtained from subjects aged 17–78 years, living in Sweden, reported that about 32.5% of adults had food hypersensitivity and among 16% immunoglobulin E-sensitized to common foods individuals, 3.0% were sensitized to almond (13).

Risk factors

Allergy to almond is a risk factor for developing an allergy to other types of nuts. A study reported multiple tree nut allergies in 19% of 2 years old children and 86% in 5 to 14 years (8). 

Environmental Characteristics

Living environment

Almond is the most important tree nut crop for commercialization. Traditionally it is the earliest temperate fruit tree crop to bud. As it is naturally self-incompatible, it frequently requires cross-pollination, which increases genetic variability and adaptability to diverse environments (1).

Almonds can survive in both moderately hot (30 to 35 oC) and cold (-2.2 to -3.3 oC) climate. The ideal soil required for almond growth is deep, loamy and well-drained. Heavy or poorly drained soils are not suitable for almond growth (14). 

Worldwide distribution

The almond is native to Central Asia, and nowadays, it is cultivated worldwide. Globally, the production of almonds reached over 1.2 million metric tons during the 2017-2018 season. Currently, the largest almond producer is the USA (81%), followed by Australia (7%), Spain (4%), Iran (1%), and Tunisia (1%) (3).

Different cultivated almond varieties have different genetic chemical profile. Their ecological and processing condition are also different (6).

The state of California in the United States is producing around 81% of the world’s almonds. Around 30 varieties of almonds are commercialized in California (6).

Almonds are used in marzipan (15). Germans regard it as the only oilseed ingredient to be used for marzipan production (16). Marzipan is either consumed directly or is used as an ingredient in baking or confectionery and as chocolate candies fillers (17).

Route of Exposure

Main

Direct sensitization by food allergens takes place by consumption only. Almonds might lead to sensitization or intolerance (2).

Detection

Oral allergy syndrome

Pollen-food syndrome is characterized by mild oral symptoms, that occur in conditions of pollen sensitization, triggered by nuts. It is also known as oral allergy syndrome. It may rarely lead to anaphylaxis. It causes when serum sIgE is directed against PR-10 homologous to those in pollen (18).

Allergic rhinitis

A single-center study in southern Taiwan included 216 patients, aged 2-93 years. The majority of the included patients had cutaneous and respiratory symptoms. The study reported a 36.97% prevalence of allergic rhinitis because of almonds in the non-sensitization group (19).

Asthma

Taiwan single-center study reported the prevalence of asthma as 13.70% for the almonds in the nut sensitization group and 7.4% in the non-sensitization group (19).

Atopic Dermatitis

In a study conducted in Taiwan, atopic dermatitis because of almonds was reported by 42.47% of 333 nut sensitized patients (19).

Other diseases

A study stated that 15% of the 1024 sensitized subjects, reported more frequent gastrointestinal symptoms, out of which 2.7% of the individuals reported symptoms due to almond (13).

Prevention and Therapy

Prevention strategies

Avoidance

Dietary management is needed to avoid the consumption of almonds. Almond sensitized people are advised to look at the packaging for ingredient details, to avoid any un-intentional ingestion of almond (18). 

Other topics

Modest amounts of nuts should be consumed during infancy and by mothers during pregnancy or lactation, to prevent the development of almond allergy in babies (11).

Molecular Aspects

Allergenic molecules

The major storage protein amandin in almond act as an allergen. It consists of 8 native almond (Prunus dulcis) allergens, but only 4 are recognized (8):

Allergen

Biochemical name

Molecular weight (kDa)

Pru du 1

PR-10 protein

17

Pru du 2S

PR-5 Protein/thaumatin-like protein

23-27

Pru du 2S albumin

Prolamin superfamily

12

Pru du 3

Prolamin superfamily

9

Pru du 4

Profilin-specific IgE

14

Pru du 5

r60sRP autoimmune reactions to human P2

10

Pru du 6

Amandin; almond major protein (AMP)

360

Pru du

γ-conglutin

45

 

Pru du 6 is an 11S globulin also known as amandin, is a major storage protein as well as a major allergen, accounting for 65% of total almond protein content. Pru du 6 leads to severe allergic reactions to almond upon ingestion. (8). Pru du 6.0101 and Pru du 6.0201 with molecular weights 61.0 kDa and 55.9 kDa, respectively have the same sequence of 57% amino acid (7).

Biomarkers of severity

Pru du 6 is a potential biomarker of almond sensitization. It has 2 isoforms that cause allergic reactions in almond sensitized people (20, 21). 

Cross-reactivity

Cross-reactivity between almond and mahleb, is of particular concern for almond-allergic patients (8). Mahleb is a cherry seed-derived spice, recognized by anti-almond antibodies including almond-allergic patient IgE. Factors that exhibited cross-reactivity with cherry kernel protein are almond-specific murine monoclonal IgG, rabbit polyclonal IgG, and almond-allergic serum IgE (22).

Birch-pollen-sensitized individuals develop pollen food allergy syndrome on the consumption of almond due to cross-reactivity. Out of subjects with birch sensitization, 71% were co-sensitized to almonds. About 83% of almond sensitized patients reported no or mild symptoms (23).

Cross-reactivity may also be with peach and other tree nut allergens (2). Pru du 3.0101 of almond shows around 99% amino acid sequence similarity with peach (7).

A study including 59 peanut-allergic adolescents and adults reported almond allergy in 46% of these patients (24).

A study reported that out of 18 almond-allergic patients, 89% were sensitized to any allergen and only 33% were positive to all the almond allergens. Pru du 8 sensitizations were found in 44% of almond allergic patients and Pru du 10 sensitizations in 67% of patients. Out of all the allergens, Pru du 6 sensitization was found to be the highest (83%) (21).

Ara h 2 (a major peanut allergen) shares the IgE-binding epitopes with that of Almond and Brazil nut allergens. This was demonstrated in a study including 17 peanut-allergic patients, wherein Ara h 2 specific serum IgE antibodies were bound to proteins present in Almond and Brazil nut extracts (25).

Apricot lipid transfer protein (LTP) has shown a sequence identity of 94% with Almond LTPs, (26).

Cross-reactivity can be observed between the Almond profilin (Pru du 4) and other profilin-containing plants (27).

An in vitro study demonstrated cross-reactivity between Pru du Amandin and a minor 50 kDa protein of Maize (a gamma-zein), however, low cross-reactivity with the 27 kDa gamma-zein was observed. The 50 kDa Maize gamma-zein reacted with IgE from pooled human sera of patients with self-reported severe Almond allergy (28).

Compiled By

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Christian Fischer

 

Last reviewed: November 2020

References
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