| Defatted Antarctic krill powder is a by-product of oil extraction from Antarctic krill(Euphausia superba).Due to its inedible properties,it is often used as low value-added products such as animal feed.It contains more than 65% high-quality protein and all essential amino acids,which meet the requirements of FAO/WHO/UNU for essential amino acid intake.Therefore,this thesis studied the extraction process of protein from defatted Antarctic krill powder,and analyzed its composition,structure and characteristics,aiming at improving the added value of defatted Antarctic krill powder products and laying a foundation for its utilization.The main conclusions are as follows:Ultrasound-assisted alkaline solution was used to extract protein from defatted Krill.The optimal conditions were as follows: Krill powder-liquid ratio of 25:1(m L/g),p H13.0,ultrasonic power of 160 W,temperature of 50℃ and ultrasonic time of 80 min.The extraction rate of protein was 97.8% and the degree of hydrolysis was 11.6%.The alkaliextracted protein was purified by acid precipitation and defluorinated on this basis.Firstly,continuous chemical-ultrasonic extraction method was used to determine the form of fluorine in the alkali-extracted protein of defatted Krill,and the proportion of watersoluble fluorine was 94.9%.Acid precipitation technology was used to purify,acid precipitation and calcium precipitation method were used to remove fluorine from the acid precipitation and acid precipitation supernatant,respectively.The defluorination rate and protein loss rate of DL-malic acid were 96.4% and 24.6%,respectively,after the acid precipitate was washed once with water(the concentration was 5%)at p H 5.0.When calcium citrate was used as the defluorination agent of acid precipitation supernatant,the protein loss rate was 5.4%and the defluorination rate was 53.3%.After ultrafiltration and spray drying,AKP-P and AKP-S powders were obtained,with a total recovery of 42.0%(dry weight)and a mass ratio of 4:1.The purity of AKP-P and AKP-S is higher than 85%,and the fluorine content is6.01±0.12 μg/g and 46.1 ±0.18 μg/g,respectively,which meet the FDA standard.SDSPAGE showed that AKP-S was degraded.AKP-P and AKP-S protein strips were identified by LC-ESI-MS/MS with: Myosin heavy chain(220 k Da,75-80 k Da),actin(40-42 k Da),β-actin(41.7 k Da),tropomyosin(32.7 k Da)and β-actin(fragment,10 k Da).AKP-P and AKP-S contain all amino acid species required by human body,and the content of each essential amino acid conforms to the amino acid limits recommended by FAO/WHO/UNU(2007)for adults and infants.SEM images showed that AKP-P and AKP-S particles were square and spherical in size,with wrinkled or smooth surfaces.FTIR analysis showed that the α-helix and random coil structure of AKP-P and AKP-S were very low or even disappeared completely.β-folding content and surface hydrophobicity vary with p H.At the isoelectric point,The β-folding content of AKP-P showed the highest value(80.7%)and the lowest surface hydrophobicity(1 009).The β-folding content of AKP-S showed the maximum value at p H 3.0(79.9%),the maximum surface hydrophobicity at p H 5.0(9988.8),and the minimum value at p H 13.0(7337.2).The results of DSC(differential scanning calorimetry)of AKP-P and AKP-S showed that both protein powders had endothermic reactions with increasing temperature and had strong thermal stability.The water absorption of them is poor,oil absorption capacity is strong.The results of animal experiments showed that the non-toxic reaction doses of AKP-P and AKP-S were 9 g/kg/d and 18 g/kg/d,respectively,which belonged to actual non-toxic substances and non-toxic substances.Compared with AKP-S,AKP-P had stronger emulsifying activity and gelation ability,and its EAI(emulsifying activity index)was positively correlated with the solubility of AKP-S.The results of rheological experiments showed that viscoelastic modulus(G’ and G’)also increased with the increase of AKP-P concentration.During heating,G’ first decreased and then increased,while during cooling,G’ increased sharply,and the gel network became stronger.Compared with AKP-P,the In vitro protein digestibility(IVPD)of AKP-S(94.87±0.78%)was significantly higher than that of AKP-P and commercial soybean protein isolate(P < 0.05).The solubility of AKP-P is greater than 70% in the range of p H 3.0-13.0,and the change trend of AKP-P solubility with p H is almost the same as that of secondary structure content.The FC(foam ability)of AKP-S was good,and reached the highest value(70.2%)at neutral condition,but FS(foam stability)was poor.In vitro antioxidant capacity of AKP-S was significantly higher than that of AKP-P(P<0.05). |
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