Tropomyosin (TM) from Antarctic krill (Euphausia superba) was extracted, purified, and identified by mass spectrometry, and its thermal stability, pH stability and digestive stability were studied. Meanwhile, sequence homology analysis, spatial structure homology modeling, and allergen mimotope peptide recognition were carried out using bioinformatics. The crude protein was extracted, thermally treated to remove impurities, precipitated at the isoelectric point and purified by salting-out. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of the purified protein showed only one clear band with molecular mass near 32 kDa. The target protein was identified as TM (Euphausia superba) by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis and UniProt database search. The molecular mass of the protein was 32.6 kDa and the peptide coverage was 97%. The results of homology analysis and physicochemical properties showed that TM from Antarctic krill was a highly conserved protein, and its sequence homology with those from 26 crustacean species ranged from 88% to 98.2%. TM from Antarctic krill had strong stability to heat, acid, alkali and gastric juice digestion, but poor stability to intestinal juice digestion, and was easily degraded by trypsin and chymotrypsin to produce low-molecular-mass peptides. Eight mimotope peptides (EAQNKETNAKADKADDEVH, DLERSEERLN, TKLAEASQAADESER, EADRKYDE, ERAEERAEAG, VSEEKANQREEAYKEQI, RSVQKLQKEVDR, VNEKEKYKGI) in Antarctic krill TM were finally predicted and identified by five bioinformatics tools including DNAStar Protean, ANTHEPROT, BepiPred 1.0 server, ABCpred server, and Immunomedicine Group, and mapped in the spatial structure. This study provides a scientific basis for the accurate prediction and identification of mimotope peptides in TM from Antarctic krill and the development of hypoallergenic products.

Antarctic krill is rich in high-quality proteins and considered to be the largest and last potential animal protein resource on the planet. At present, Antarctic krill is mainly processed into primary products such as Antarctic krill powder and frozen Antarctic krill meat rather than high value-added products. This article systematically reviews the nutritional properties and evaluation, functional properties and modification, functional activity and mechanism of action, and safety of Antarctic krill proteins, which will hopefully provide research ideas for the deep processing and comprehensive utilization of Antarctic krill proteins.

This study examined changes in the degree of hydrolysis, peptide yield, digestibility, and hydrolyzed amino acid content during the simulated gastrointestinal digestion of Antarctic krill protein. Furthermore, the in vitro proosteogenic activity of different concentrations of the lyophilized residue from the supernatant of the digestion product at the optimal digestion time was evaluated. The results showed that the hydrolysis degree, peptide yield, digestibility, and hydrolyzed amino acid content in the supernatant from Antarctic krill protein digestion increased significantly with digestion time, reaching an equilibrium after 120 min of intestinal digestion, with a hydrolysis degree of 42.67%, a peptide yield of 35.30% and a digestibility of 82.21%. The supernatants at all digestion time points enhanced the osteogenic activity of mouse MC3T3-E1 osteoblasts, the one obtained after 120 min of intestinal digestion being the most effective. Living/dead cell staining, alkaline phosphatase (ALP) activity assay and alizarin red staining confirmed that the supernatant from intestinal digestion for 120 min had good cellular compatibility, promoted osteoblast differentiation and mineralization and consequently regulated its osteogenic activity by enhancing ALP activity and intracellular calcium deposition. The results of this study provide a theoretical basis for the high-value application of Antarctic krill protein.

Shrimp (Penaeus vannamei) proteins have been shown an allergenic potential; however, little information is available on the sensitizing and eliciting capacity of shrimp protein digestion products. In this study, a BALB/c mice model was used to explore the allergenicity of shrimp protein sample (SPS) and their gastric and gastrointestinal digestion products (GDS/GIDS). As compared with the SPS groups, the GDS/GIDS groups caused lower specific immunoglobulins (IgE/IgG₁) levels (P < 0.05), but higher than the control groups, indicating that the digestion products sensitized the mice. Meanwhile, spleen index, mouse mast cell protease-1(mMCP-1) concentration and proportion of degranulated mast cells were significantly reduced in the GDS/GIDS groups (P < 0.05); simultaneously, allergic symptoms, vascular permeability and histopathological changes of tissues were alleviated. Nevertheless, the allergenicity of digestion products cannot be eliminated and still cause systemic allergic reactions in mice. The study showed that the digestion products of shrimp still had high sensitizing and eliciting capacity.

Enzymatic hydrolysis, isolation, and purification might make a great deal of difference in antioxidant activity and antigenicity of peptide components. This study aimed to isolate and purify antioxidant peptide components from Antarctic krill and evaluate their allergenicity of them. Electron paramagnetic resonance (EPR) spectroscopy results indicated 310 kDa Antarctic krill hydrolysates (AKHs) had higher DPPH and ·OH radical scavenging rates. And the second component (N2-2) purified 310 kDa hydrolysate showed better ability to scavenge DPPH and ·OH radicals (P < 0.05), which were (47.43 ± 2.18)% and (34.33 ± 1.25)%, respectively. Additionally, indirect-ELISA results revealed that N2-1 had a weaker ability to bind specific IgE and that N2-2 had a lower binding capability to specific IgG1 (P < 0.05). And N2-2 had a higher EC₅₀ value of (5.29 ± 0.95) ng/mL (P < 0.05) in cell degranulation assay, which was about 13.80 times that of Antarctic krill. Therefore, N2-2 might be the potential source of the antioxidant peptides with lower allergenicity.