Enzyme Combination、Desalination And Biochemical Properties Of Grass Carp Peptides

In this paper, grass carp proteins were hydrolyzed by enzyme combination toproduce grass carp peptides. The desalination methods of grass carp peptides wereselected between NF and mixed ion exchange resin, its biochemicalcharacterization after desalination was analyzed, which provide importanttheoretical to improving grass carp peptides in food industry.Alcalase was selected from six proteases, the optimum hydrolysis conditionsfor it are as follows: concentration of grass carp30%, pH9.0,50℃, ratio of alcalaseto grass carp protein48AU/kg, time210min. Under these conditions, the peptidesrecovery rate for grass carp proteins is57.3%, contents of peptide is76.3%. Theoptimum com-bination(alcalase and neutrase) was screened through alcalaseremixing with other protease, the peptides recovery rate for grass carp proteins wasmarkedly increase using the group. The kinetic model of enzyme combination forgrass carp proteins was obtained by RSM：Y=-41.445833+61.408333A+24.98333B+34.445833C-13.783333A2-2.60000AB-19.883333B2-1.750000AC-1.10000BC-7.645833C2Comparied with experiment result, the kinetic model fits well. It shows thekinetic model has significant application value. the optimum hydrolysis conditionsare as follow: hydrolysis time of alcalase2h, hydrolysis time of neutrase0.5h,alcalase and neutrase2:1(w/w), Under these conditions, the peptides recovery ratefor grass carp proteins is61.26%, contents of peptide is80.9%.The grass carp peptides were separated by ultrafiltration with10000MWCO,contents of peptide were reduced from81.9%to80.9%, contents of ashes wereincrease from16.6%to17.5%. The grass carp peptides were desalted by NF with200～2000MWCO, the results showed that concentration of peptides was1%,pressures0.5MPa, time12min, under these conditions, the desalination rate was65.1%, while the peptide recovery rate was50.5%. The grass carp peptides weredesalted by mixed ion exchange resin, the results showed that pH7.0, flow rate6BV/h, proportions of anion and cation1︰2～2︰3, under these conditions, thedesalination rate was81.7%, while the peptide recovery rate was80.5%. Comparewith two methods, the results showed that mixed ion exchange resin is better. Thecontent of ashes, water and peptides in grass carp peptides after desalination was3.2%,5.6%and90.3%.Biochemical characterization of grass carp proteins and peptides before andafter desalination were measured, compare with grass carp proteins, the grass carppeptides had good solubility, which was over95%in the large pH range(pH2～ 10);it had a low viscosity which was4.5mPa·s when concentration of peptides was40%. The moisture-absorption and moisure-retention of grass carp proteins andpeptides were investigated. The moisture-absorption and moisture-retention ofgrass carp peptides were higher than grass carp proteins, under humidity30～90%condition, moisture-absorption increased from0.5%to28.65%. Moisture-retentionwas good that water left rate was17.0%at silica gel condition for48h. Thedistributing of molecular weight for grass carp proteins and peptides weredetermined by HPLC. The results showed the molecular weight above1500Da was77.4%in grass carp proteins; the molecular weight of grass carp peptides wasmarkedly decrease, which ranged from190～1000; the molecular weight of grasscarp peptides before and after desalination have no significant difference. Thecontents of amino acid for grass carp proteins and peptides were determined byamino acid composition analyzer, Comparing with grass carp proteins, most of theamino acid composition have no significant difference in grass carp peptides. Inaddition, the total content of six essential amino acid (Thr,Val,Ile,Leu,Phe,Lys)were increase from16.6%to22.5%. The average hydrophobicity of grass carpproteins and peptides were calculated according to the contents of amino acid. Theresults showed the average hydrophobicity of grass carp proteins and peptides was3.55kj/mol and4.57kj/mol.