EUROPEAN SEABASS Dicentrarchus labrax ALLERGENICITY AND FISH QUALITY AFTER EDTA SUPPLEMENTATION

Introduction

Allergies to fish are a significant public health concern throughout the world and show sensitization prevalence’s of up to 2.9% in the general population [1]. The main fish allergen is β-parvalbumin; a small and highly stable muscle protein, and responsible for 95% of the allergic responses. Fish parvalbumins are highly conserved proteins, which bind bivalent ions, like calcium or magnesium. Previous works showed that EDTA is a calcium chelator and might reduce the IgE-binding capacity of the main fish allergen, due to a structural rearrangement resulting in an apo-form. The objective of this study was to diminish the allergenic potential of European seabass through the supplementation of EDTA in fish diets.

Methodology

Twenty-two European seabass juveniles with an initial body weight (IBW) of 174 ± 1.29 g were reared in 500L conical tanks for 98 days. Four different experimental diets were tested (in triplicates) namely, Control (CTRL, commercial diet without EDTA supplementation), 1.5, 3 and 4.5% of EDTA supplementation in the commercial diet, which will be referred as EDTA1.5, EDTA3 and EDTA4.5, respectively. Fish were reared under optimal environmental (dissolved oxygen above 5 mg L-1) and natural photoperiod conditions. Fish were fed twice a day by hand, ad libitum. All fish were lethally anaesthetized with tricaine methanesulfonate (MS-222) and sampled for biochemical and quality analysis. Proteins from muscle samples were used for allergenicity quantification by sandwich IgE-ELISA using serum from fish allergic patients.

Results

At the end of the trial, the fish final body weight (FBW) was not significantly affected by any of the diets (Table1). However, feed conversion ratio (FCR) was negatively affected by the EDTA4.5 diet when compared to CTRL (one-way ANOVA, followed by post-hoc Tukey, p<0.05).

Fish quality, muscle pH and rigor mortis index were measured during the first 72 h post-mortem. Muscle pH decreased with time without showing significant differences between the experimental diets. Fish reached almost a full rigor index 24 h post-mortem with significant differences at T1 (1 hour post-mortem) and T48. As mentioned, supplementation with EDTA would induce the apo-form of parvalbumin, a less allergenic structure due to the blocking of the functional epitopes of the protein. The analysis of IgE-reactivity using fish allergic patients’ serum (n=6) showed no significant differences in the modulation of parvalbumin and therefore supplementation with EDTA up to 4.5% seems not to reduce the allergenicity of European seabass. 

Conclusion 

Dietary EDTA supplementation preserved fish quality as edible food product. IgE-ELISA showed that the supplemented chemical into fish feed was unable to modulate fish allergenicity.

As future works a different rearing technique will be tested to reduce the allergenic potential of European seabass. Also, different post-mortem treatments will be studied in the two mean Mediterranean species, European seabass and gilthead seabream.

Acknowledgements

This work received Portuguese national funds from FCT- Foundation for Science and Technology through project UID/04326/2020. This work integrates in project 16-02-01-FMP-0014- Allyfish co-financed by Mar2020 (4107IDNAD50308.18). Denise Schrama and Cláudia Raposo de Magalhães acknowledge FCT for PhD scholarships (SFRH/BD/136319/2018 and SFRH/BD/138884/2018)

Bibliography

1.                        Klueber, J.; Schrama, D.; Rodrigues, P.; Dickel, H.; Kuehn, A. Fish Allergy Management: From Component-Resolved Diagnosis to Unmet Diagnostic Needs. Curr. Treat. Options Allergy 2019, 6, 322–337, doi:10.1007/s40521-019-00235-w.