How different processing tech impact seafood allergy?

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Seafood encompasses fishes and shellfish which provide a good amount of easily digestible proteins, polyunsaturated fatty acids and vitamins to the consumers. Global acceptance and increased frequency of consumption of seafood is linked to its nutritional advantages. But among seafood, fish and shellfish are one of the eight major food allergens as per Food and Agriculture Organization of the United Nations (FAO) and World Health Organisation (WHO) owing to their allergic responses in sensitive individuals. There are many food processing technologies to ensure the safety of food, modification of texture, enhancement of taste or colour and to make it digestible. Let’s explore some of the most efficacious technologies.

Food allergy is an important public health concern globally not only in developed nations but also in developing nations and is the abnormal immunological response to certain food proteins by sensitive individuals which is mainly mediated by immunoglobulin E (IgE). 

Globally, around 170 different foods are linked with allergic reactions and food allergy impacts 1–2 per cent of adults and 3–6 per cent of children living in developed countries. The crustacean allergy affects more than 2 per cent of the global population and the USA, European Union (EU) and Japan insist mandatory labeling of food allergens including crustaceans. 

The variation in reporting of food allergies and absence of information gathering systems make it more prevalent than actual. Seafood allergy can persist throughout the life of 90 per cent of the patients. Overall, the incidence of shellfish allergy is more in Asian countries than other developed nations. Huge consumption patterns of seafood and early exposure to life from childhood in Asia make shellfish as the most common food allergen especially in older children and adults. 

Shellfish are the primary foods causing anaphylaxis in South-East Asia and mild oral symptoms like itching and lip swelling are also reported in Asian population.

The most important and useful management strategy for allergic responses is the avoidance of allergic food. The crustaceans causing allergy are shrimps, crabs and lobsters in the order of incidence. 

Many researchers have attempted to reduce or eliminate the allergenicity of crustaceans by different processing methods. Allergic proteins identified from crustacean sources are tropomyosin, arginine kinase, sarcoplasmic calcium-binding protein, myosin light chain, troponin C and hemocyanin. Among these allergens the most commonly reported one is tropomyosin.

Among shrimp allergies, 80 per cent are triggered due to tropomyosin. Although tropomyosin from invertebrates is reported as a major allergen, tropomyosin from vertebrate sources is non-allergic. Arginine kinase is the second major allergen after tropomyosin in shrimps. Studies have revealed that crustacean arginine kinase along with tropomyosin can cause sensitivity in crab processing workers through respiration.


Processing methods and crustacean allergenicity

There are many food processing technologies to ensure the safety of food, modification of texture, enhancement of taste or colour and to make it digestible. 

In addition to the traditional practice of thermal processing methods, many non-thermal methods are also evolved to minimise the nutritional quality loss. Crustaceans are also processed in different ways and the allergic protein components can be altered by the modifications in the structural components and hence the allergenicity. 

The epitope, the stretch of amino acids in an allergen binding with the IgE leading to allergic reactions, can be linear or conformational epitopes, depending on the primary structure of the protein. 

The study by Dr Laly under the supervision of Dr Sankar indicated that processing can alter immunodominant epitopes and can potentially affect allergenic properties either by destruction of existing epitopes or by formation of new epitopes or neoallergens. Conformational epitopes are more vulnerable to processing induced destruction, while the linear epitopes are more likely to be altered by hydrolysis, chemical modifications or by mutations. The structural changes of protein and allergenicity can vary with the processing method and also on the type of food material. 

Application of thermal and non-thermal processing methodology can modify physical and chemical characteristics of proteins leading to the change of allergenic epitopes. Although complete removal of allergenic ability by processing is rather difficult to achieve, reduction in the allergic threshold could be accomplished by the appropriate conditions.

For instance, shrimp allergenic activity is reported in cooking oil regardless of shrimp in breaded or non-breaded form. Hence the usage of the same cooking oil containing shrimp allergen can transfer the allergen to other non-allergic food materials. The high temperature during frying elevates the antigenicity by 6 to 8 times.

Frying process can alter the allergenicity by removal of existing protein epitopes to reduce allergenicity or may create new epitopes to increase allergenicity. Autoclaving, a moist heating technology used for sterilisation, is reported to alter the action of many food allergens.

On the other hand, microwaves can modify the native structure of proteins and could lead to changes in protein recognition by IgE. A comparison of different thermal processing methods like boiling, steaming, frying, baking, grilling and microwave cooking has demonstrated that microwave treatment alone is not sufficient to reduce the proteins antigenicity and has to be combined with other treatments to reduce allergenicity. 

The non-thermal processing techniques such as high pressure processing, gamma irradiation, pulsed electric field etc. do not contribute to heating of food to make alteration in the product and hence, is expected to retain most of the nutritional benefits as well as organoleptic characteristics in comparison to thermally treated foods. Besides, chemical and enzymatic treatments can also be applied to modify or cross link the allergic protein. 

Enzymic hydrolysis of allergenic proteins is a gentle and harmless method to degrade food allergens. It can be done either by cross linking to bury IgE reactive epitopes or by proteolytic hydrolysis to make proteins into small peptides. Different proteases used in the food industry for cross linking are transglutaminases, peroxidases, laccases and tyrosinases.

Attempts to reduce the crustacean allergenicity by treating with acidic medium have also been reported by a few researchers. Immunogenicity of shrimp tropomyosin after vinegar marination at varying pH of 1.0 to 4.8 indicated significant reduction in IgE binding potential at pH 1.0-3.5 compared to that at higher pH.

However, the advantages of combined treatments in hurdle technology approaches can make effective mitigation of crustacean allergenicity and can be suitably optimised for hypoallergenic food development. 

The hurdle technology approach can enhance safety and stability of food material along with the retention of nutrients and sensory properties. There are reports indicating the reduction in IgE activity of shrimp allergen by the combined effect of gamma irradiation and boiling.

Thus, suitable processing technology for preparing hypoallergenic food is to be optimised together with the development of analytical tools for detecting hidden allergens in trace levels which can protect sensitive individuals. 


Dr T V Sankar, Principal Scientist, Indian Council of Agriculture Research – Central Institute of Fisheries Technology (ICAR-CIFT)

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