Evaluating the risks of fish allergy from thermostable allergens in canned fish

By Vijay Kumar MalesuReviewed by Lily Ramsey, LLMSep 4 2023

In a recent study published in Allergy, researchers evaluated the safety of consuming canned fish for fish-allergic patients by analyzing the immunoreactivity of serum from fish-allergic subjects and assessing the content and integrity of parvalbumin (PV) in canned fish products.

Study: Thermostable allergens in canned fish: Evaluating risks for fish allergy. Image Credit: DulceRubia/Shutterstock.com

Background

Fish allergy, a global Immunoglobulin E (IgE)-mediated condition without a cure, persists lifelong in almost 90% of patients and is typically managed through avoidance. Some fish-allergic individuals tolerate canned fish; however, the reasons remain unclear.

Canning might reduce allergenicity by altering protein structures, but comprehensive studies on canned fish allergens are sparse.

Allergic reactions to canned fish highlight the allergenic potential, underscored by heat-resistant allergens like PV, tropomyosin (TM), and collagens that remain intact despite cooking. Further research is crucial to ensure the safety of canned fish consumption for individuals with fish allergies.

About the study

In the present study, pediatric patients aged one to 18 with clinically confirmed fish allergies were recruited from the Children's Hospital at Westmead, Australia, and their sensitization was assessed using diagnostic tests like skin prick testing and the detection of specific IgE.

If these patients or their parents showed interest in incorporating canned fish into their diets, and a history of tolerance to canned fish was unclear, they underwent oral food challenges with canned fish like tuna or salmon.

Serum from patients without seafood allergies was used as a control, and the research was conducted ethically, with all guardians providing informed consent while maintaining patient confidentiality.

Researchers purchased canned fish products, including salmon, tuna, and sardine, from major Australian supermarkets, reflecting a significant portion of products available in the country. Protein extracts from these canned products and specific fresh fish types were prepared for further analysis.

Immunoblotting with specific antibodies was utilized to detect the presence of the allergen PV in the fish. Additionally, to understand the binding of IgE in allergic reactions, serum from the recruited patients was analyzed, and this serum was further subjected to mass spectrometry to identify the exact proteins that bind with IgE.

Lastly, the identified sequences of two major allergens were analyzed and compared for similarities.

Study results

The study focused on understanding the protein profiles in various canned fish products, specifically looking at the allergenic properties of these proteins. 

In the analysis of canned fish products, a significant variance was observed between the protein profile of the canned fish and that of the Crude Extracts (CEs) from the same fish.

Specifically, proteins in the canned products seemed more aggregated or degraded, resulting in a lack of distinctive bands on the protein profiles.

The study found no significant difference in the protein profiles of canned salmon from different species or manufacturers. However, distinctions were noted between canned skipjack (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares), containing smaller proteins and larger ones.

Additionally, the allergen PV was not detected in any canned fish products, even though it was present in salmon and sardine CEs.

Moreover, some proteins in the canned fish products were found to bind to specific Immunoglobulin E (sIgE), with most of the binding occurring for proteins larger than 30 kDa.

The extent of sIgE binding varied between fish types; for example, yellowfin tuna exhibited more sIgE binding than skipjack tuna. Moreover, while salmon and sardine CEs demonstrated strong sIgE binding to proteins between 11-14 kDa, tuna CE lacked this pattern.

Mass spectrometry techniques identified major fish allergens, including PV and TM, as the sIgE-binding proteins. In-depth analysis revealed that these proteins were in varying quantities across different canned fish products.

For example, canned pink salmon contained significant percentages of PV and TM, while canned sardine contained abundant amounts of PV and TM. Interestingly, although not officially recognized as a fish allergen, myosin heavy chain was found in all canned products.

The data collected showed that 66% of the 53 fish-allergic patients exhibited sIgE binding to canned fish proteins, with canned sardine recording the highest percentage of sIgE binding, succeeded by canned salmon and tuna.

The specific proteins to which patients' sera bound varied, but a significant portion was bound to smaller proteins in canned salmon, a pattern also noted in cooked salmon. Sardine exhibited frequent sIgE bindings, especially in certain protein weight ranges, and this trend was also observed in salmon and tuna.

Finally, an analysis of amino acid sequences of fish allergens revealed that TMs were more conserved across the fish species than PVs.

While TMs from sardine and salmon were found to be 84-90% similar, the PV isoforms exhibited less similarity, with many only being up to 80% alike.

Conclusions

In the detailed study of 17 canned fish varieties, researchers found variations in protein composition between canned and cooked fish. Despite high heat processing, major fish allergen PV was still present in canned fish.

Another allergen, TM, showed even stronger allergic reactions than PV, suggesting its importance in canned fish allergenicity.

With Myosin heavy chains also detected, the safety of consuming specific canned fish for allergic individuals requires personalized assessment.

The complexity of allergens in canned fish highlights the need for tailored guidance for fish-allergic patients considering canned fish consumption.