Allergenicity Reduction of Antarctic Krill (Euphausia superba) Tropomyosin through Glycosylation Modification

Antarctic krill (Euphausia superba) was a premium protein resource. However, its strong allergenicity remained a problem that awaited resolution. To reduce the allergenicity of Antarctic krill tropomyosin, monosaccharides (ribose, glucose) and oligosaccharides (mannooligosaccharide, galactooligosaccharide) were used for glycosylation. Results showed that glycosylated tropomyosin underwent a decrease in free amino groups and an increase in molecular weight. Meanwhile, the secondary structure experienced a transition from α-helix to β-sheet, the exposure of aromatic amino acid residues to a hydrophobic environment resulted in decreased fluorescence intensity of glycosylated tropomyosin. These findings demonstrated that four kinds of sugars successfully glycosylation with tropomyosin. The glycosylation degree of tropomyosin and the modification of its allergenic epitopes were further investigated using liquid chromatography-tandem MS. Results revealed that the glycosylation degree of monosaccharide glycosylated tropomyosin significantly higher than that of oligosaccharide glycosylated tropomyosin (P<0.05), and that the number of glycosylation sites on allergenic epitopes of tropomyosin modified by mannooligosaccharide and galactooligosaccharide was 9 and 11, respectively, higher than those of tropomyosin modified by ribose and glucose, which showed 8 and 8, respectively. Results from the BALB/c mice model showed that the mice gavaged with glycosylated tropomyosin exhibited reduced allergic responses compared to those gavaged with tropomyosin, including lower levels of IgE, IgG1, IL-4, mast cell degranulation, histamine, vascular permeability, and intestinal permeability. It was worth noting that the mice gavaged with galactooligosaccharide-glycosylated tropomyosin showed a more pronounced reduction in allergic responses, which was attributed to the fact that galactooligosaccharide modified more allergen epitopes of tropomyosin than ribose, glucose, and mannooligosaccharide. This study provided a theoretical basis for reducing the allergenicity of Antarctic krill tropomyosin and developing hypoallergenic shrimp products.