Property Characterization Of Bioactive Protein/Peptide And Chitin From Antarctic Krill(Euphausia Superba)

Recently, Antarctic krill (Euphausia superba) has been widely studied andextensively recognized as a target for commercial fishing. Antarctic krill has a largerbiomass comparing with all other aquatic species currently harvested. It is rich inprotein of high quality and food safety. As a new type of food raw material, thedevelopment and high-value utilization of Antarctic krill may provide an effective wayfor solving food shortages with population growth. Supported by the starting-point ofAntarctic krill utilization, this study was carried out with three critical-points, includingphosphoprotein, bioactive peptide, and chitin. It aimed at offering a theoretical basisand technical support for utilizing Antarctic krill efficiently. Major conclusions weresummarized：(1) Defatted krill powder was prepared from fresh krill by extinguishing enzymeand removing lipid in turn. Antarctic krill phosphoprotein was obtained by guanidinehydrochloride extraction, dialysis, and lyophilization. It contained2.69%ash, no lipid,10.14ppm fluorine, and0.89%phosphorus. Protein electrophoresis of Antarctic krillphosphoprotein showed three distinct bands with different molecular weights (51kD,35kD,18kD). Infared spectrum analysis suggested hydroxyl phosphorylation occurredin the side chains of protein. It maintained a good solubility and thermal stability. Inaddition, Antarctic krill phosphoprotein could prevent calcium from forming insolubleprecipitation in neutral water condition, indicating a potential ability in promotingcalcium absorption and organization mineralization.(2) Defatted krill powder was prepared from fresh krill by extinguishing enzymeand removing lipid in turn. Bioactive peptides were recovered from defatted krillpowder using trypsin, neutral protease, and alkaline protease. Protein recovery yieldswere all over70%. Ash and sugar contents of peptides were lower than7.0%and3%, respectively. No lipid was detected in the peptides. The fluorine contents of krillpeptides were lower than15ppm. The amino acid and element compositionscorresponded to recommended intake. Properties of krill peptides were characterizedemploying infared spectra, SDS-PAGE, and RP-HPLC technologies. Different totryptic peptides, peptides produced with neutral and alkaline proteases presentedsimilar characters. Krill peptides produced with neutral protease and alkaline proteasecould inhibit the ACE activity in vitro effectively, with IC50values of0.18mg/mL and0.21mg/mL. Krill peptides produced with trypsin maintained better anti-oxidant andCa-solubling activities in vitro.They may possess potential abilities in promotingcalcium absorption and organization mineralization.(3) Antarctic krill chitin was extracted from krill shells in different ways. Chitinof high quality was obtained by using1.7M HCl,2.5M NaOH and1%potassiumpermanganate in turn. Crystalline structure and thermal properties are characterized byemploying Fourier transform infrared spectroscopy, X-ray diffractometry, scanningelectron microscopy, thermogravimetry, and differential scanning calorimetry. It wasconcluded that Antarctic krill chitin corresponded to being α-polymorph, and wascomposed of small, stable, and uniform microcrystals. The degree of N-deacetylationwas11.28±0.86%. The d-spacings of Antarctic krill chitin were9.78and4.63at(020) and (110) planes. The crystalline sizes were6.07nm and5.16nm at (020) and(110) planes respectively. The activation energy of the polysaccharide chaindecomposition was123.35kJ/mol and the glass transition (Tg) of Antarctic krill chitinwas164.96°C.