| Zinc has positive regulatory on human growth and development,the loss of zinc would cause the disturbances of physiological condition in human body,leading to the slow growth,low immunity,and decreased sexual function.Unlike conventional zinc supplements(inorganic zinc,organic zinc and amino acid zinc),it is worth noting that the oligopeptide can react with zinc ions to form zinc chelate peptides,which have a more stable structure and better water solubility,thereby increasing the bioavailability of zinc,and is beneficial to increasing the biological activity of zinc and oligopeptides,providing an idea for the development of functional zinc supplements.Antarctic Krill has abundant biological reserves,high protein content and outstanding bio-potency.In addition,Antarctic krill powder has the advantages of low circulation cost and convenient storage,and is an ideal protein source for preparing zinc chelate peptide.However,it is currently used for direct preparation of animal feed.In this paper,Antarctic krill powder was used as raw material,the composition characteristics of raw materials were analyzed,and the protein components were enriched and defluorinated.The preparation process of oligopeptide was established,and zinc chelate peptide was successfully prepared,its structure and tolerance to the gastrointestinal environment in vitro were further illuminated.Finally,a zinc chelate peptide gelatin was developed,which provides a technical basis for the development of ready-to-eat foods containing zinc chelating peptides for Antarctic Krill powder.The main results were as follows:(1)The main components of Antarctic Krill powder as protein,oil,chitin and mineral elements,as well as the composition of amino acids,fatty acids and mineral elements were analyzed.The results showed that the content of protein was 61.38%,lipid was 14.49%,chitin was 6.08%and mineral element was 6.27%.The total amino acid content was 47.34%.In addition,the essential amino acid content was 38.74%,accounting for 70.24%of the non-essential amino acid content,and the functional amino acid content is outstanding;it could be considered to that Antarctic krill powder is a high-quality protein source recommended by FAO/WHO.The content of unsaturated fatty acids in oils and fats was 61.98%,including polyunsaturated fatty acid content of 25.10%,EPA+DPA+DHA content of 18.19%.Antarctic Krill powder is rich in mineral elements(K,Na,Mg,Ca,P,Fe,Cu,Zn,Sn),and the levels of heavy metal pollution(Cr,As,Cd)were extremely low.And after degreasing by n-hexane-ethanol(9:1 by volume)with a sieve(30 mesh),the protein content in the powder base reached 73.80%,but the fluorine content was 1268.56±21.36 mg/kg,which far exceeded the FAO limit standard(≤100 mg/kg),indicating that the defluorination treatment may needs to be considered.(2)The 5 basic components and 18 hydrolyzed amino acids of Antarctic Krill powder were determined,including with or without sieving,degreasing and defluorination treated.The results showed that with the treatment of screening,degreasing and defluorination,the protein content of Antarctic Krill powder increased from 61.38%to 73.80%,the total protein loss rate was 9.27%,and the defluorination rate was 82.03%.The amino acid content has reached the amino acid rating standard in premium fishmeal and is a high-quality protein source as approved by FAO/WHO,indicating that sieving,degreasing and defluorination treatments increase the protein content without changing the protein composition pattern.(3)The single factor-response surface test was used to optimize the enzymatic hydrolysis process,and the mathematical model of enzymatic hydrolyzed ceramic membrane microfiltration was established.Finally,the basic components,amino acid composition and molecular weight distribution of the enzymatic hydrolysate were studied.The optimum conditions for the final enzymatic hydrolysis(alkaline protease-flavor protease)process are as follows:pH is 7.50,enzymatic amount is4024 U/g,enzymatic hydrolysis temperature is 46℃,enzymatic hydrolysis time is 3 h,and the degree of hydrolysis under this condition is 43.80±1.41%.The best pressure of the ceramic membrane was 2×10~5 Pa and the permeability of the peptide molecule accords with the ExpAssoc model,the transmittance of the microfiltration 360 min peptide reached 82.86±6.37%.The protein fluoride content obtained by enzymatic hydrolysis and ceramic membrane microfiltration was 26.57 mg/kg;the amino acid composition of the peptide is comprehensive.The ratio of peptides which molecular weight was less than 1000 Da has reached 91.3%.The weight average molecular weight was 340 Da,which consistent with the quality requirements of oligopeptides.(4)Using Antarctic krill oligopeptide as a raw material,the single factor-orthogonal test was used to optimize the process of preparing zinc chelate peptide by zinc sulfate method.Ultraviolet spectroscopy,Fourier transform infrared spectroscopy,thermogravimetric analysis,X-ray diffraction,scanning electron microscopy-energy spectroscopy,amino acid composition and molecular weight distribution were used for qualitative and quantitative analysis.Finally,zinc sulfate and zinc gluconate were used as controls.Tolerance of zinc chelate peptides was investigated by in vitro mimicking the gastrointestinal environment.The results showed that the optimum process parameters for zinc chelate peptides are as follows:the ratio of oligopeptide-zinc volume is 3:1,pH is 6.0,temperature is 60°C,chelation time is 1.0 h,and the chelation rate of zinc ions was 76.31%in this condition.Otherwise,the formation of the chelate was confirmed by ultraviolet spectroscopy,Fourier transform infrared spectroscopy,and other analysis.The results of the amino acid composition and molecular weight distribution of the zinc chelate peptide showed that the content of aspartic acid,glutamic acid,lysine,histidine and cystine increased significantly,the proportion of peptide molecules in the zinc chelate peptide at 180-480 Da is 64.47%.It can be inferred that the structure of the peptide in the chelate is mainly a small peptide which composed of 2-4 amino acid sequences.The tolerance of zinc chelate peptide to mimic the digestive environment in vitro showed that the intestinal zinc ion solubility and zinc ion dialysis rate of zinc chelate peptide were higher than that of zinc sulfate heptahydrate and zinc gluconate,and the ultraviolet spectrum and Fu before and after simulated digestion.There was no significant change in the infrared spectrum of the inner lobe,indicating that the zinc chelate peptide has good structural stability during digestion.(5)The process of antarctic krill protein source zinc chelate peptide gelatin was studied by fuzzy mathematics-single factor method.The optimum process parameters for zinc chelate peptide gelatin are as follows:zinc chelate peptide is 1.52%,gum is37.88%,white sugar is 45.44%,orange juice is 3.03%,starch syrup is 12.12%,and citric acid is 0.1%.Under this condition,the comprehensive sensory score of the gelatin gum was 84.42±4.13,representing a good sensory quality.Ultraviolet spectroscopy,Fourier transform infrared spectroscopy and in vitro simulated digestion showed that the zinc molecules in the zinc chelate peptide were chemically bonded to the gelatin system,which was stable in the gelatin system and had a potential for production as a ready-to-serve zinc supplement. |
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