Abstract
BackgroundMany types of shellfish including oysters are sometime cooked before ingestion and it has been demonstrated that cooking may affect the allergenicity of food. Therefore, the aim of our present study is to identify major and minor allergens of tropical oyster (Crassostrea belcheri) and to investigate the effect of different cooking processing on the allergenicity of this oyster.MethodsRaw, boiled, fried and roasted extracts of oyster were prepared. Protein profiles were analysed using sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE). Major and minor allergens and allergenicity patterns of all extracts were then determined by immunoblotting with sera from patients with positive skin prick tests (SPT) to the raw oyster extract. Mass-spectrometry was used to identify the major allergenic proteins of this oyster.ResultsSDS-PAGE of the raw extract showed 15 protein bands (20–180 kDa). In contrast, smaller numbers of protein bands were demonstrated in the boiled extract, those ranging between 40–42 and 55–150 kDa were denatured, whereas the protein profiles were altered to a similar degree by frying or roasting. The 37 kDa proteins had the highest frequency of IgE-binding (95 %), thus identified as the major allergen of this tropical oyster. Other minor IgE-binding proteins were observed at various molecular weights. Immunoblot of raw extract yielded 11 IgE-binding proteins. The cooked extracts showed only a single IgE-binding protein at 37 kDa. Mass spectrometry analysis of the 37 kDa major allergen identified this spot as tropomyosin.ConclusionsCooked extracts produce lower IgE-binding than raw extract, which suggest that thermal treatment can be used as a tool in attempting to reduce oyster allergenicity by reducing the number of IgE-reactive bands. The degree of allergenicity of this oyster was demonstrated in the order raw > boiled > fried ≈ roasted. A heat-resistent 37 kDa protein, corresponding to tropomyosin, was identified as the major allergen of this tropical oyster.
Highlights
Many types of shellfish including oysters are sometime cooked before ingestion and it has been demonstrated that cooking may affect the allergenicity of food
It is well documented that the ingestion of oyster, skin and mucosal contact and the inhalation of aerosolized oyster proteins during cooking or in an occupational setting can cause a large variety of clinical symptoms in sensitized patients, such as urticaria, angioedema, atopic dermatitis, asthma, rhinitis, vomiting, diarrhea and anaphylaxis [2,3,4]
Fewer bands were detected in the boiled extract as several protein bands between 40–42 and 55–150 kDa were sensitive to heat and were no longer detected in the gel
Summary
Many types of shellfish including oysters are sometime cooked before ingestion and it has been demonstrated that cooking may affect the allergenicity of food. Oysters are naturally one of the most nutritionally well balanced of foods [1]. They are low in fat, calories and cholesterol in addition to being high in protein, iron, omega 3 fatty acids, calcium, zinc and vitamin C [1]. Oysters are one of an elicitors of IgEmediated type I allergy [2,3,4]. The only effective treatment to prevent oyster-induced allergies is a specific avoidance diet [5]. Avoidance is often difficult due to unintentional cross-contamination or the addition of oyster as ingredients in some common sauces and condiments [5]
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