Functional Properties Of Protein Isolates And Fe²⁺ Chelate Peptides From Large Yellow Croaker ?Pseudosciaena Crocea? Roe

Large yellow croaker?Pseudosciaena crocea?is one of the most important fish in China.However,a mass of roe,accounting for 20%of the fish weight,is produced as the low value by-product.With the development of the large yellow croaker industry,the efficient use of P.crocea roe is urgently needed.P.crocea roe is rich in protein and fat,which can be used to prepare functional food bases.Therefore,this paper uses the dried powder of P.crocea?pcR?as raw material to prepare the protein isolates and lipids,to compare the functional properties of different protein isolates,and to explore the Fe²⁺chelation ability and cause of the hydrolysates.Firstly,the method of preparation of protein isolates and lipids from pcR was established based on the protein recovery rate index,and the extraction conditions were determined by single factor experiment.The results showed that both 0.6 mol/L NaCl?pcRPI-NaCl?and pH2 HCl?pcRPI-HCl?solutions could recover protein from pcR,and the protein recovery rates reached 70.10%and 64.68%,respectively.The pcRPIs are rich in essential amino acids?40.80%-41.70%?.Next,protein isolates were analyzed by SDS-PAGE and NanoLC-ESI-MS/MS system,the result confirmed that main components of protein isolates were vitellogenin,vitellogenin B and vitellogenin C.Compared with pcR,protein isolates had better solubility,water/oil holding capacity and emulsifying abilities.Compared with the pcRPI-NaCl,pcRPI-HCl had better water/oil holding capacities and emulsifying activity,but pcRPI-NaCl had better emulsifying stability.Compared with soy protein isolate,pcRPI-HCl and pcRPI-NaCl had better oil holding capacities,emulsifying activity and emulsifying stability?pH 2-4 and pH 6-9?.In addition,compared with pcR,the surface hydrophobicity,total sulfhydryl groups,free sulfhydryl groups and disulfide bonds of pcRPIs-HCl was significantly increased.But compared with pcR,the surface hydrophobicity and free sulfhydryl groups of pcRPIs-NaCl were significantly increased,while the total sulfhydryl groups and disulfide bonds remain unchanged.Compared with pcR,the?-helix and?-turn content of the pcRPI decreased,the?-sheet content increased,but the random curl did not change significantly.All these results indicate that the protein isolates can be used to prepare functional food bases.Finally,the enzymatic hydrolysis of papain and trypsin were used to investigate the Fe²⁺chelation ability of the pcR hydrolysates.The results showed that the pcR was hydrolyzed by papain and trypsin for 3 h,the hydrolysis degree reached 6.42%and 20.53%,respectively.And the oligopeptide with molecular weight of 0.5-1 kDa was dominant in pcR hydrolysates.The Fe²⁺chelating ability of pcR hydrolysates were further analyzed by flurazazine reagent.The results showed that the chelating ability of the trypsin hydrolysate was significantly higher than that of papain hydrolysate and the semi-inhibitory concentration(IC₅₀)was 0.145and 0.219 mg/mL,respectively.The amino acid composition,infrared spectrum and fluorescence spectrum of the hydrolysate and Fe²⁺-hydrolysatechelate were analyzed.These results indicate that the NH₂,-COOH and C=O groups in the hydrolysate are involved in chelation.On this basis,the enzymatic peptide sequence was obtained by computer simulation,and it was confirmed by sequence analysis that some peptides in the hydrolysate may participate in Fe²⁺chelation.These results showed that the protein isolates and lipids from P.crocea roe were obtained by using NaCl and HCl solutions.The trypsin hydrolysate of P.crocea roe had strong Fe²⁺chelation ability.This study provides a good research basis for further development of P.crocea roe resources.