Preliminary Study On Processing The Protein Of Antarctic Krill

Antarctic krill is an abundant resource, which have a high quality of protein, and there is no good technology for krill protein utilizing at present. For this, we did principium study of the crude krillase, autohydrolysis, and enzymolysis for ACE inhibit peptide and flavoring. Details of this paper were as follows.1. The crude krillase have been characterized by biochemical and electrophoretic techniques. Casein digestion assay revealed that there existed acidic proteases with optimum activities at pH 3.0 and pH 6.0, and alkaline proteases with optimal activities at pH 7.5 respectively in the Antarctic krill. The optimum pH 3.0 protease with thermal stabilities is confirmed to be a pepsin-like, the optimum pH6.0 protease with thermal instabilities and inhibited by PMSF is confirmed to be a carboxypeptidase A, the optimum pH7.5 protease with thermal stabilities and inhibited by SBTI is confirmed to be a trypsin-like proteinase.2. The technology of autohydrolysis was investigated about Antarctic krill and mathematical model was established for autohydrolysis of Antarctic krill. Results of single factor experiment suggested that 12 hours was optimum hydrolysis time. The result of the response surface experiment suggested that the effect from three factors (temperature, initial pH and material ratio) was prominent on the content ofα-amino nitrogen in supernatant. The process of autohydrolysis could be predicated well and truly by the mathematical model. Optimum conditions of autohydrolysis were as follows, temperature (43.21oC), initial pH (7.48), and material ratio (0.58:1). The result of verification test demonstrated that the content ofα-amino nitrogen in autohydrolysis supernatant attained to 0.38±0.018g/100ml. The predicted value of equation was 0.39g/100ml and the good coherence lied in between them. Results of autohydrolysis could be predicted well and truly by the mathematical model.3. Established a method for determination of ACE inhibitor activity by HPLC. When the content of FAP was during 0.005-0.5 mmol·L-1, the content of FAP was linear relationship well with its area. The least limit of detectability was 0.5μmol L-1, the coefficient of recovery was 99.53-102.72% for FAP, and RSD is 1.48%(n=6)in the method. ACE inhibitory peptides were prepared from Antarctic krill protein by five commercial proteases (bromelin, neutrase, pepsin, trypsin, papain), and their ACE inhibitory activity were determined in vitro by HPLC. Trypsin hydrolysate was found to have the highest ACE inhibitor activity. Effects of temperature, initial pH, time and enzyme to substrate ratio on ACE inhibitor activity were studied by response surface experiment, the result indicated that the optimum conditions for hydrolysis were as follows, temperature (37.5oC), initial pH (7.66), time (5.05 hours), E/S ratio (0.15%, (W/W)). The IC50 of hydrolysate of trypsin under the optimum conditions was 2.22±0.11g/mL. Separating hydrolysate by ultrafiltration, we found that the molecular weight of the highest activity of ACE inhibitory peptides was 1-2KD.4. Antarctic krill was autohydrolysate at the optimum conditions, and then added five commercial proteases (bromelin, neutrase, pepsin, trypsin, papain) to hydrolysis for seafood flavoring. Results of chemistry and sensory index indicated that trypsin was the best enzyme. response surface experiment of three factors (temperature, initial pH and enzyme to substrate ratio) for establishing mathematical model which suggested that the optimum conditions for hydrolysis were as follows, temperature (44.85oC), initial pH (7.98), E/S ratio (1.15‰, (W/W)). The result of verification test demonstrated that the content ofα-amino nitrogen in hydrolysis supernatant attained to 0.690±0.012g/100ml. The predicted value of the equation was 0.694±0.0093 g/100ml and the good coherence lied in between them. The result of hydrolysis could be predicted well and truly by the mathematical model.5. Volatile flavor compounds were extracted by SPME and were detected by GC-MS in trypsin hydrolysate of Antarctic krill. Detection results demonstrated that main volatile compounds were 59 compounds which consisted of 10 acid compounds, 7 alcohol compounds, 13 carbonyl compounds, 8 ester compounds, 5 nitrogen compounds, 5 sulphocompounds, 3 furan compounds, 3 phenol compounds, and 5 hydrocarbons. The major volatile compounds involved of 1,2-Benzenedicarboxylic acid bis(2-methylpropyl) ester, 1,2-Benzenedicarboxylic acid, 2- ethylhexyl ester, 5-methyl-2-phenyl-1H-Indole, 5-(2-Aminopropyl)-2-methylphenol , 5,6-2H-2,4,6-trimethyl -4H-1,3,5-dithiazine, 4-allyl-5-(1-naphthylmethyl)-1,2,4-Triazole-3- thiol and so on.