Study On Protein Preparation And Active Peptides From Elaeagnus Mollis Diels Seed Kernels

The chemical compositions of Elaeagnus mollis Diels seeds were preliminarily analyzed.Then,the common methods of extracting plant protein were compared.The extraction rate of protein was higher through alkaline extraction and acid precitation.The extraction process was optimized by single-factor and orthogonal array designs.Functional properties of protein from Elaeagnus mollis Diels seeds were investigated systematically.Then,the four protein components were obtained from Elaeagnus mollis Diels seeds by Osborne fractionation,and their amino acid contents and compositions were analyzed.The nutritional values of Elaeagnus mollis Diels seeds protein were evaluated by fuzzy pattern recognition and ratio coefficient of amino acid.The contents of taste-active amino acids and therapeutic amino acids were also analyzed.The process of proteolysis was optimized and the antioxidant of peptides was studied.The research contents and results are as follows:(1)Elaeagnus mollis Diels seeds kernels contained 50.87% crude fat,36.27% protein,2.91% starch,5.50% water and 3.10% ash.Protein content is slightly lower than the soybean protein content,2 times of walnut protein content.(2)The common methods of extracting plant protein were compared.The extraction rate of protein was higher through alkaline extraction and acid precitation.The optimal parameters for extraction were determined as follows: p H,11.0;S/L ratio,1:50(g/m L);extraction temperature,55 ?;extraction time,2.0 h;and two extraction cycles.Under these conditions,the extraction yield of protein was 93.85% with a purity of 84.81%.(3)The factors,for example,temperature,p H,Na Cl concentration have great influence on the functional properties of Elaeagnus mollis Diels seeds kernels.The water-holding capacity and oil-absorbing capacity of the proteins extracted ranged from 1.2 to 1.8 g/g and 2.8 to 3.3 g/g,respectively.The foaming capacity and the emulsifying capacity could reach 190% and 25 m2/g under optimum p H conditions.(4)Elaeagnus mollis Diels seeds protein contained 17 kinds of amino acids of which including 7 kinds of essential amino acids.Essential amino acids accounted for 25.9% to 30.0% of the total amino acids in Elaeagnus mollis Diels seeds kernels.(5)Among these proteins,the SRCAA value of water-soluble protein was the highest(83.51),followed by gliadin(75.45)and salt-soluble protein(69.09),and alkali-soluble protein had the lowest SRCAA value(66.44).The nutritional values of the water-soluble,salt-soluble and alkali-soluble proteins were closer to that of whole hen's egg protein,suggesting that they are high quality plant proteins.The first limiting AA in the water-soluble protein was Thr,while the first limiting AA in the salt-soluble protein,gliadin and alkali-soluble protein was Met+Cys.All the four proteins were rich in both taste-active amino acids and therapeutic amino acids,indicating that E.mollis seed kernels have a great potential to be developed and utilized for flavored foods and medicinal foods.(6)By comparing the effect of different enzymes on the degree of hydrolysis and the yield of polypeptide,the 2709 alkaline protease was finally determined as the enzyme for polypeptide preparation.The optimal enzymolysis conditions were determined as follows: temperature of enzymolysis was 50 ?,enzyme concentration was 2000 u/g,substrate concentration was 6%,p H was 9.0,and the optimum conditions of enzymatic hydrolysis were determined by orthogonal test.The hydrolysis degree is 28.90%,and the yield of polypeptide is 65.47%.By measuring the reducing power of the polypeptide and the scavenging rate of DPPH free radicals,it was concluded that the sperminin polypeptide had certain antioxidant activity and the antioxidant capacity of selenoprotein increased with the increase of its concentration.