Study On The Preparation And Application Of Fish Collagen Peptide Chelating Calcium

Fish by-products are rich in collagen,which are good sources for the preparation of collagen peptides.Collagen peptide chelating calcium based on shark cartilage,shark skin and tilapia skin were prepared by the method of enzymatic hydrolysis in this study.The secondary structure,microscopic structure,the primary structure of the components and effects on promoting calcium absorption in rats of calcium-binding peptide were investigated.In chapter 2,the optimum technology of preparing shark cartilage collagen peptide chelating calcium was obtained by single factor test and orthogonal test.The optimum conditions were as following:enzymatic hydrolysis time 1 h,enzyme quantity 0.25%and substrate concentration 25 mg/mL,and the calcium binding ability of co llagen peptide was up to 1087.01mg/100g protein.The result of HPLC showed that the molecular weight distribution of shark cartilage collagen peptide chelating calcium was focused below 4000 Da.The content of acidic amino acids?glutamic acid and aspartic acid?and hydrophobic amino acids were 12.67 and24.87 g/100g protein,respectively.The results of FTIR showed that the absorption peaks of-NH₂ and-COOH were in 3345cm^-1 and 1653cm^-1,respectively.It can be observed that shark cartilage collagen peptide chelating calcium presented tight structure via SEM.In chapter 3,shark skin collagen peptide was separated and purified by hydroxyapatite affinity chromatography,and the peptide exhibited the strongest calcium binding ability was further identified by UPLC-Q-TOF-MS,the result showed that F₄ was consist of three components,with the molecular weight of 585.4 Da,678.5 Da and 791.6 Da,and the corresponding amino acid sequences were Leu-Asp-Thr-Ala-Phe,Ala-Tyr-Ala-Glu-Leu-Leu and Ser-Ser-Phe-Leu-Leu-Leu-Leu,respectively.On the other hand,collagen peptide with the highest calcium binding ability derived from tilapia skin was selected by the method of adding exogenous calcium into peptides,the calcium binding ability was up to 107.8 mg/g protein.Two sequences of tilapia skin collagen peptide with the highest calcium binding ability were identified by Q-TOF-MS/MS,whose amino acid sequences were Ser-Ala-Pro and Glu-Gly-Leu respectively.Compared with the primary structure of calcium-binding collagen peptide derived from shark skin and tilapia skin,both of them exhibited stronger hydrophobic property with a high content of hydrophobic amino acids,meanwhile,they contained one or two amino acids which could bind calcium?Asp,Glu,Ser,Thr?,thus endowed collagen peptide with better capability of binding calcium.The FTIR spectra analysis of tilapia skin collagen peptide and peptide-calcium complex demonstated that the characteristic absorption peaks of the-NH₂ and-COOH were moved from 3313.9 and 1541.9 cm^-1 to 3357.1 and 1551.5 cm^-1,respectively.The intensity of the peak in 1397 cm^-1 which belongs to-COO-was decreased,while the peak of1449.1cm^-1 was increased,elucidated that both of the-NH₂ and-COOH of the tilapia skin collagen peptide were involved in the coordination reaction.According to the result of SEM spectra,it was found that calcium could embed in the collagen peptide.In chapter 4,we evaluated the effect of collagen peptide chelating calcium?FCP-Ca?on promoting calcium absorption in mice.As a result,the calcium absorption rate and retention rate of FCP-Ca group were significantly higher than those in control group and CaCO₃ group.Compared with the control group,the calcium-phosphorus ratio in serum of low-dose FCP-Ca group and middle-dose were increased,the content of femur weight,bone density,bone calcium and hydroxyproline were also improved to a certain extent.These results indicated that FCP-Ca not only can promote the calcium absortion of mice,but also can make them absorb and utilize collagen peptide,and thereby facilitate the synthesis of collagen.