Screening Of Symbiotic Microbes Of Antarctic Krill And Preparation And Activity Research Of Antioxidant Peptides

Antarctic krill resources are the world's largest source of animal protein resources,but for a long time most of its application were in aquaculture and other low value-added industries,bioavailability was low.In recent years,extensive research and application of bioactive peptides led to people extract active peptides from a variety of proteins.In this paper,Antarctic krill was used as an experimental material to ferment with the commensal bacteria isolated from Antarctic krill,and the active antioxidant peptides were obtained.The fermentation conditions were optimized with reducing power as the index.The Amino acid sequence of the purified peptides were analyzed and the antioxidation activity of Antarctic krill peptides was studied in vivo and in vitro.First,10 strains of symbiotic strains were isolated from Antarctic krill,and the Antarctic krill was fermented with the symbiotic strain.The antioxidation of the fermentation broth was determined by hydroxyl radical scavenging power and reducing power.The results showed that the NL-6 fermentation broth hydroxyl free radical scavenging rate and reducing power were 91.7% and 0.804.The NL-6 strain was identified as Psychrophacter by physiological and biochemical characterization and 16 S r RNA sequence analysis.The fermentation conditions of Antarctic krill were optimized by the response surface method(RSM)and the optimum fermentation conditions were as follows: medium ratio: 6.4g / 50 ml,fermentation time 30.4h,fermentation temperature 36.8 ?,and the actual relative reducing power of Antarctic krill fermentation broth was 0.679(the difference between NL-6 fermented broth reducing force and the same quality Antarctic krill reductive force),While the same quality Antarctic krill culture medium reducing power was 0.412,so after the response surface optimization of antioxidant peptides,the actual reducting power was1.091,there was no significant difference between the actual values and forecast(P<0.05).The fermented liquid centrifuged and separated into four groups with different molecular weight divided by ultrafiltration fractionation,AKF-I(MW > 10 k Da),AKF-II(5 MW-10 k Da),AKF-III(MW 0.5-5k Da)and AKF-IV(MW < 0.5 k Da),AKF-III components have the best antioxidant activity after freeze-dried,when 10mg/m L,hydroxyl free radical scavenging,the reducing power,DPPH radical scavenging.and ABTS+ radical scavenging were 74.1%?0.998?56.2%?89.7%,fluorine content(178 ± 3.4mg / kg)to meet the EU standards,this component separated by preparative RP-HPLC,then P2 component reducing power was 1.214,and through LC-MS / MS the amino acid sequence of the related antioxidant peptides were analyzed.The in vitro and in vivo stability studies of antioxidant peptides from Antarctic krill showed that the AKF-P2 had good thermal stability,after the effect of high temperature with 2h,hydroxyl free radical scavenging rate remains above 89%,reducing power remained at more than 87%;when p H is alkaline,hydroxyl radical scavenging rate decreased slightly(about 14%)compared with the control group,AKF-P2 reducing power was 12.6% higher than the control group when p H was 8;Under the sunlight,with the increase of storage time,hydroxyl radical scavenging activity decreased obviously,at day eighth,the hydroxyl radical scavenging activity was reduced by 76.3%;In the presence of each metal ion,AKF-P2 hydroxyl radical scavenging rate was almost unaffected,but the reducing power was affected by metal ions,when the concentration of Cu2+ was 5mmol /L,the reducing power decreased by 93% compared with the control.Ca2+has the least effect on the antioxidant activity of AKF-P2.Therefore,health food containing AKF-P2 can be used with various calcium supplement products,and its antioxidant activity is almost unaffected.Gastric digestive environment simulation showed a greater impact with hydroxyl radical scavenging,after pepsin and trypsin double digestion,hydroxyl free radical scavenging rate decreased by about 70%,while after pepsin and trypsin digestion,the reducing power was almost the same,only reduced about 15%.