The Comparative Study Of Cashew Nut Protein On Structure And Functional Properties Prepared By Different Extraction Methods And Protein Purification Exploration

Cashew nut is rich in nutritional value,considered as one of the high-quality protein and fat sources.This research took cashew nut as raw materials and the comparative study of cashew nut protein on structure and functional properties prepared by different extraction methods and protein purification exploration were investigated systematically.The latter includes using Osborne extraction method by four-step to separate the different components in cashew nut protein,comparing its functional properties and structure and using gel chromatography for further purification and study.The results showed that:(1)Using alkali extraction and acid precipitation and salt soluble method to extract cashew protein,obtained CNPI and CNSPI,with purity of 80.7%and 91.4%.By comparing the functional properties and structure of CNPI and CNSPI,we found that different extraction methods have significant differences(p<0.05)on the structural and functional properties of cashew nut.In neutral environment,CNPI had better solubility,foaming and foaming stability and higher surface hydrophobicity.While,CNSPI had a higher protein purity,emulsification(30.14 m~2/g)and emulsion stability(138.58 min).SDS-PAGE and amino acid analysis showed the subunit composition and amino acid composition of cashew nut protein prepared by different methods were very similar and cashew nut protein was rich in glutamic acid and aspartic acid,and was mainly composed by a 53 kDa subunits which is formed by a32 kDa polypeptide chains and a 21 kDa polypeptide chains via disulfide bond.On the morphology,CNPI exhibited smooth surface and large sheet structure and CNSPI exhibited irregular,small spherical particles.In addition,CNPI had less?-helix and random coil compared with CNSPI.It is suggested that the alkali extraction and acid precipitation process can cause great degree of denaturation of cashew nut protein compared with salt solving processing which would result the differences in their functional properties.(2)Using Osborne four-step extraction method to obtained four components via crude purified cashew nut protein,namely albumin,globulin,prolamin,glutelin with purity of 83.60%,95.51%,20.52%,81.30%.Protein content in decreasing order was:globulin>albumin>glutelin>prolamin.The solubility of cashew nut albumin,globulin,glutelin was increased with increasing pH.In neutral environment,albumin and globulin almost completely dissolved and the solubility of glutelin also reached79.88%.Both of them were far higher than commercially soy protein isolate in solubility.Gluten had the best performance in water holding capacity,oil holding capacity,foaming and foaming stability,while the surface hydrophobicity value of glutelin was also the highest,which indicated that glutelin is a typical amphiphilic protein.And albumin was the in emulsifying properties which was higher than globulin and glutelin,and all of them were superior than isolated soy protein.The proportion of amino acid composition in albumin,globulin,glutelin was good,which the content of valine,isoleucine,leucine,lysine could meet the FAO/WHO/UNO standard recommended for children and the content of threonine,leucine in glutelin was close to the recommended standard for children.SDS-PAGE analysis showed that there is a large similarity existed in polypeptide chain of albumin and globulin,but there is a clear difference with glutelin:albumin and globulin were mainly composed by a 53 kDa subunits which is formed by a 32 kDa polypeptide chains and a 21 kDa polypeptide chains via disulfide bond;the molecular weight of glutelin is great;prolamin primarily had two polypeptide chain with molecular weight of 17,9kDa.The major secondary structure of albumin,globulin,glutelin was?-sheet.Compared with the large sheet structure of glutelin,albumin and globulin had a similar microtopography which showed many globular mixed with other irregularities.It is suggested that the different ingredients composition,molecular weight and the presence of different protein conformation in albumin,globulin,glutelin can significantly affect the functional properties of them.(3)Using gel chromatography for further separation of cashew nut albumin,globulin,glutelin and found that albumin mainly had three components,respectively,with the molecular weight of>669 kDa,13.7-29 kDa,6.5 kDa;globulin containing mainly four components,respectively,with the molecular weight of>669 kDa,253-440 kDa,13.7-29 kDa,6.5 kDa;glutelin had a single component,with one distinct peak and large molecular weight.By comparing different elution flow rate and eluent found that choosing pH 7.0,0.01 M PBS(containing 0.15 M NaCl)eluent at a flow rate of 0.2 mL/min was benefit for protein separation.