Study On Desalination Processes Of Salted Egg White And Preparation For Antioxidant Peptides

The methods of desalination of salted egg white were studied in this thesis.In addition,emzymatic hydrolysis of egg white to produce protein hydrolysates with antioxidant activity was investigated.The main results were as follows:1.Ultrafiltration(UF) membranes with different molecular weight cut-offs(MWCOs)of 10kDa,30kDa and 50kDa were used to desalinate salted egg white.The membrane with MWCO of 30kDa was selected as the optimal membrane because it had a relatively higher permeate flux,desalting rate and more than 90% protein retaining rate.The orthogonal test showed that the optimum desalination effect could be obtained under the conditions of pressure at 0.22MPa,temperature at 50℃and dilution ratio 1∶2.5.2.The degree of hydrolysis(DH) and bitterness value of hydrolysates obtained by four kinds of proteases were studied and papain was chosen as the biocatalyst for egg white protein hydrolysis.3.The impact of the factors such as protease/substrate ratio,temperature,initial pH and duration of reaction on DH and bitterness value of egg white protein hydrolysates.On the basis of one-way tests,optimum conditions to achieve the maximum DH of hydrolysis procedure were determined by response surface analysis(RSA):[E]/[S]=3700U/g,temperature at 50℃and initial pH=8.0.DH was 23.2% and bitterness value was 1.3 under the optimal conditions.4.In order to deodorize egg white protein hydrolysates,several methods were carried out.The results showed that the effect of deodorization was not significant while citric acid,ethanoic acid,active carbon and L-cysteine hydrochloride was used respectively.Bothβ-CD and yeast were able to remove unpleasant odor from egg white protein hydrolysates.The optimum method was 3%(w/w)β-CD in 50℃for 45min or 0.6%(w/w) yeast in 35℃for 2.5h.5.HPLC analysis showed that 47.31% essential amino acids and 22.89% antioxidant amino acids in egg white protein hydrolysates were much higher than native egg white protein with 36.64% essential amino acids and 12.32% antioxidant amino acids. 6.The antioxidant activity of egg white protein hydrolysates by papain was evaluated by different analytical methods in vitro.The results showed that egg white protein hydrolysates had the antioxidative activeties and radical scavenging activites.The half inhibitory concentration(IC50) of 1,1-diphenyl-2-picrylhydrazyl(DPPH),hydroxyl radicals and speroxide anion were 3.8mg/mL,0.36mg/mL and 0.85mg/mL respectively.7.The effect of temperature,pH and storage time on the antioxidation stability of egg white hydrolysates was investigated.The results showed that the antioxidant peptide from egg white protein has a strong heat-resistant and storage stability but loses its activity easily in the alkali environment.