Preparation,Structural Characterization And Bioavailability Of Antarctic Krill Peptide-Zinc Chelate

Antarctic krill is an important polar fishery resource and the most potential animal protein resource.At present,the land-based processing of Antarctic krill is mainly based on production of Antarctic krill oil,and the by-product degreased Antarctic krill power has not been effectively used,resulting in a waste of Antarctic krill resources.Zinc is one of the necessary trace elements for the human body,which nutritional effect is closely related to the process of human growth and development.Compared with conventional zinc supplements,peptides-zinc chelate can directly be absorbed in the form of chelate,avoiding the influence of the intestinal environment and the competition of coexistents,which can improve the bioavailability of zinc.In this paper,the firstly was to optimal preparation conditions of Antarctic krill metal chelate protein peptide material(AKP)using degreased Antarctic krill powder as the raw material.The secondly was to prepare the Antarctic krill peptides-zinc(AKP-Zn)chelate and detect the structure and composition characteristics by instrumental analysis techniques.The thirdly was to evaluate zinc absorption effect of the AKP-Zn chelate by in vitro simulated gastrointestinal digestion experiment and in vivo animal experiment.The results would lay the foundation for the utilization of the Antarctic krill protein resource and developing a novel zinc supplement.In this paper,with the degree of hydrolysis as the main indicator and Zeta potential as the secondary indicator,the optimal enzyme was selected to prepare Antarctic krill metal chelate protein peptide material among five proteases,including alkaline protease,trypsin,acid protease,neutral protease,and papain.Then under the optimal temperature and pH conditions of the optimal enzyme,with the degree of hydrolysis as the response value,single factor experment and response surface experment were implemented to optimize the process parameters such as enzymatic hydrolysis time,enzyme dosage,material to liquid ratio,physical and chemical properties of the AKP were analyzed.The results showed that trypsin was the most suitable protease for the preparation of AKP under the two indicators of degree of hydrolysis and Zeta potential.The relevant process parameters were determined as enzymatic hydrolysis time 2.75 h,enzyme dosage 2.50%,material to liquid ratio 1:3,and the degree of hydrolysis could reach up to 14.16±0.43%.Zeta potential of AKP was-29.83±0.66 m V,and the percentage content of peptides with molecular weight of<3000 Da in the AKP accounted for 90.27±0.05%.In addition,Glu,Asp,Lys and other amino acids with metal chelate capacity accounted for 31.91±0.45%of the total amino acids.The above results indicated that AKP was a good protein peptide material for preparing metal chelate.Zinc content in the AKP-Zn chelate as the index and the prepared AKP as the raw material,the reaction pH,temperature,time,and the mass ratio of AKP to Zn SO₄·7H₂O were optimized,structure characterization and composition analysis of the AKP-Zn chelate were resolved.The results showed that the zinc content reached 115.70±2.25mg/g when the mass ratio of the AKP to Zn SO₄·7H₂O of 1:2,pH 6.0,60°C and 10 min,which is the best condition for preparing the AKP-Zn chelate.The Fourier transform infrared spectroscopy showed that the characteristic absorption peaks of amide bond I,II,IV and-COO-have changed,indicating that zinc was chelated with the carboxyl oxygen and amino nitrogen atoms in the AKP.The size distribution of the AKP-Zn chelate moved to 3460.33±146.36 nm,and the Zeta potential increased to-10.20±0.72 m V.After the chelation reaction,the percentage content of peptides with molecular weight of>1000 Da in the AKP-Zn chelate significantly increased to 58.11±0.54%,and the total contents of Glu,Asp,His,Lys and Arg in the AKP-Zn chelate significantly increased to 50.30±0.33%.The microscopic analysis of the AKP-Zn chelate showed that the surface of AKP-Zn chelate was rough and loose,and the proportion of zinc enhanced significantly.In addition,AKP-Zn chelate has good stability under different pH conditions,the zinc retention rate of AKP-Zn chelate achieved 60.39±1.36%at pH 8,which was significantly better than zinc sulfate and zinc gluconate.This part of the study proved that under the optimized preparation process conditions,an effective chelation reaction between zinc and AKP,and the AKP-Zn chelate had good stability.The differences between the AKP-Zn chelate and zinc supplements in terms of digestion stability in vitro and zinc absorption in vivo were compared through in vitro simulated gastrointestinal digestion experiments,24 h digestion and absorption experiments and 14 d short-term intragastric administration experiments.Under the conditions of simulated gastric digestion,the zinc retention rate of the AKP-Zn chelate was not significantly different from other zinc supplements,while in simulated intestinal digestion conditions,the zinc retention rate of AKP-Zn chelate can maintain41.65±1.56%,which was significantly higher than that of zinc sulfate and zinc gluconate.The results of simulated gastrointestinal digestion experiments showed that AKP-Zn chelate had better stability under intestinal digestion conditions.In addition,under simulated gastric digestion conditions,the characteristic infrared absorption peak of the AKP-Zn chelate weakened or even disappeared,while under simulated intestinal digestion conditions,the characteristic absorption peak regenerated,indicating that after gastrointestinal digestion,zinc ions eventually remained in the form of a chelate.In the24 h digestion and absorption experiment,the plasma zinc concentration of AKP-Zn chelate appeared at a peak after 2 h after intragastric administration of SD rats with AKP-Zn chelate,returned to the initial level at 24 h;bioavailability was higher than that of zinc sulfate and zinc gluconate.In the 14 d short-term intragastric administration experiments,there were no significant differences in body weight,organ index and plasma zinc content of SD rats in each experimental group.The accumulation of zinc in the bones,liver,kidney,spleen and other organs of rats in the AKP-Zn chelate group was slightly higher than that of other zinc supplement groups,suggesting that AKP-Zn chelate has the potential to improve the bioavailability of zinc ions.The results of this part proved that AKP-Zn chelate has good digestion stability,can be absorbed by organisms in the form of chelate,and reaches close to or even slightly better than zinc gluconate and other zinc supplements in absorption and utilization effect.The research results can provide scientific support for the application of AKP-Zn chelate as a zinc supplement.