Latin name: Brassica napus
Source material: Whole seeds
Common names: Rape seed, Rapeseed, Canola, Oilseed Rape
Brassica napus is a quite variable species, with 3 important subspecies:
- B. napus napobrassica (rutabagas or swedes)
- B. napus pabularia (Siberian kale, Hanover salad, etc.)
- B. napus oleifera (Rape seed)
Rape is an annual plant similar to the turnip and rutabaga. It is thought that Brassica napus originated from a hybridisation between the turnip (B. rapa) and kale (B. oleracea acephala). Rape originated in northern Europe and was cultivated near the Mediterranean Sea, but is now grown throughout the world. Canola, a selectively bred variant of Rape, was developed in the late 1970s in Canada as a more nutritious source of vegetable oil than Rape seed.
The Rape plant is an annual or biennial growing up to 1.2 m, with yellow flowers that in their season make Rape fields a striking sight. At the same time, the released volatile organic compounds (there are 22 altogether (1)) create a distinct smell. The slick, turnip-like flat leaves are 10 to 30 cm long. Unlike turnip, Rape has no swollen root, only a thin taproot. Sickle-shaped pods containing tiny round seeds are produced.
This plant has become a very common crop in the UK and elsewhere. Rape is generally grown in large fields for green livestock fodder, birdseed or Rape seed oil.
Canola is a new type of Rape grown commercially for the seed, which is lower in saturated fats and fatty acids than the original cultivar. Canola oil is also almost free of erucic acid, a toxic compound plentiful in older varieties.
Canola oil has become a common ingredient in both homemade and commercial foods.
Rape seed contains 2 main storage proteins, a high-molecular-mass legumin-like 12 S globulin and a low-molecular-mass 2 S protein (also known as napin or nIII) (2-4,6, 9).
The 2 S protein has been characterised as the following:
- Bra n 1, a 2S albumin (napin); the protein consists of 2 different chains of 9.5 and 4.5 kDa (5-12).
In a study to identify possible major allergens in Rape seed and Turnip rape using sera from 72 atopic children with positive SPT to these proteins, major reactivity was demonstrated to a group of homologous, approximately 9.5 to 14.5 kDa proteins that were identified as 2S albumins (napins). Approximately 80% of the patients had IgE antibodies to purified napins from both plants. In SPT using purified napins, positive reactions were demonstrated in all 6 children tested (12).
Rape seed is able to generate chitinase when wounded, as demonstrated by a study in which complementary and genomic DNA strands coding for a Brassica napus chitinase have been cloned and sequenced (13-14). The allergenic potential of this protein is not known to date.
Low-molecular-mass trypsin isoinhibitors have been isolated (but their antigenicity is unknown) (15).
A 2S albumin recombinant protein from the seeds of Brassica napus was shown to have a high thermal stability, and these results suggest that rproBnIb, like other 2S albumins, may be able to reach the gut immune system intact (11).
An extensive cross-reactivity among the different individual species of the family could be expected to occur clinically with Rape seed (16). A study of children sensitised to Rape seed reported that the high correlation in the skin reactivity between Rape seed and Turnip rape suggested cross-reactivity, and this is supported by the fact that they both contain homologous 2S albumins (17).
The 2S albumin storage protein in Rape seed exhibits extensive sequence similarity with 2S albumins from other seeds. Cross-reactivity between Mustard and Rape seed flours as a result of this protein has been reported (6). Similarly, the Mustard allergen Sin a 1 was found to be related to other low-molecular-mass albumins, such as those isolated from Rape seed, Castor bean and Brazil nut. Structural similarity was also reported between the glutamine-rich large chain of Sin a I and a proline-rich zein, a gliadin, and trypsin and alpha-amylase inhibitors isolated from the seeds of several monocotyledons (18).
Rape seed protein may induce symptoms of allergy in sensitised individuals, predominantly in occupational settings such as animal feed factories, grain mills and farms. Individuals may be sensitised to either Rape seed as a food or Rape seed pollen as an inhalant. For allergy to the pollen, see Rape w203.
A 48-year-old man who had been working in a feed processing plant suffered episodes of wheezing with shortness of breath after exposure to Rape seed flour. After 5 years of exposure, he noted sneezing and rhinorrhoea whenever the flour was being discharged from the mill and he was in the vicinity. Symptoms subsided 2 hours after the exposure ended. He also developed oedema and pruritis of the lips, oral mucosa and pharynx, and facial urticaria immediately after ingestion of a small amount of Mustard sauce. The reactions were attributed to cross-reactivity with the 2S albumin allergen from Rape seed flour and Sin a 1 from Mustard (6).
A 48-year-old man, employed in a grain and animal feed store for 9 years, reported rhinorrhea, sneezing, nasal obstruction, ocular burning, coughing and wheezing, which had all occurred over the previous 12 months and were induced by Rape flour (19).
A 43-year-old male working in the grain industry experienced cough and chest tightness during working hours. SPT was positive to Rape extract. A broncho-provocation test was positive. The study results confirmed that the inhalation of Rape dust, not pollen, was the cause of his IgE-mediated occupational asthma (20). Similarly, a study demonstrated that inhalation of Rape flour caused bronchoconstriction, induced an eosinophilic inflammatory bronchial response, and increased bronchial hyperresponsiveness in sensitised asthmatic farmers. Contact with the allergen took place through its presence as flour in animal fodder (21).
In a Finnish study, skin prick testing for suspected food allergy in young children with atopic dermatitis frequently found positive reactions with Turnip rape and Rape seed. A subsequent study of 1,887 Finnish children, who were screened with SPT for sensitisation to Turnip rape and Rape, found that 206 (10.9%) had reactivity for Turnip rape and/or Rape seed (9.3% for Turnip rape and 9.4% for Rape seed). Twenty-five (89%) of 28 children enrolled in the challenge study showed a positive challenge reaction to Turnip rape. Seventeen reacted with labial whealing after labial challenge, and 8 had facial urticaria, flare-up of atopic dermatitis or abdominal symptoms after oral challenge. One child developed rhinitis. Four children had immediate symptoms within 3 hours, and 4 experienced delayed reactions. Allergen-specific IgE determination for Turnip was positive in 17 of those positive to labial challenge. Three challenge-positive children showed a flare up of atopic dermatitis when the oral challenge had lasted for 2-5 days. The high correlation in skin reactivity between Rape seed and Turnip rape suggested cross-reactivity, and this is supported by the fact that both substances contain homologous 2S albumins (17).
In a subsequent study, 64 of these children, with atopic dermatitis and the presence of skin reactivity IgE to Turnip rape and/or Oilseed rape, were assessed for any common sensitisation pattern to certain foods or pollens, and were shown to have significantly more prevalent skin- and serum-specific sensitisation to various foods (Cow's milk, Egg, Wheat, Mustard) and pollens (Birch, Timothy, Mugwort) than a control group (22).
Pure Rape seed oil is reported not to cause allergic reactions (23). However, occupational allergic contact dermatitis from PEG-4 Rape seed amide in massage oil has been reported (24).
In the 1980s, Spanish toxic oil syndrome occurred as a result of the presence of aniline as a permitted adulterant for imported French Rape seed oil; this caused disease in 20,000 people and over 2,500 deaths. The toxic oil syndrome was a multisystemic disease brought on by the ingestion of Rape seed oil denatured with 2% aniline (25-26).
Compiled by Dr Harris Steinman, email@example.com
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