Study On The Preparation And Adsorption Purification Mechanism Of Low Phenylalanine Egg White Peptides

The establishment of an efficient preparation technology of low-phenylalanine peptide is essential for the development of special medical formula foods that meet the needs of patients with phenylketonuria.However,this technology is limited by the restricted protein sources and poor specificity of adsorbents until now.In this study,egg white protein with characteristics of high nutritional value and digestible was selected as the raw material,to prepare lowphenylalanine peptides by step-by-step hydrolysis combined with activated carbon adsorption technology.The adsorption mechanism of activated carbon to phenylalanine residues in the hydrolysates was also discussed,so that the theoretical guidance for the efficient preparation of low phenylalanine peptides can be obtained.The main research contents of the thesis are presented as follows:Alkaline protease I was used to hydrolyze the egg white protein solution after different pretreatments,adopting the degree of hydrolysis as the indicator.It was determined that heating combined with shearing is the optimal pretreatment method for egg white protein,which can effectively improve the efficiency of subsequent enzymatic hydrolysis,promotes the release of phenylalanine in the protein and lays the foundation for the efficient removal of phenylalanine.On the basis of pretreatment,a two-step enzymatic hydrolysis method was used to hydrolyze the egg white protein,adopting the degree of hydrolysis and the free-phenylalanine efficiency as indicators.The specific process of the two-step enzymatic hydrolysis was clarified:in the solution of egg white protein concentration of 3%(w/v),8%(w/w)trypsin was firstly added and hydrolyzed for 7 h at 37℃ and pH 8.0,and then 7%(w/w)flavourzyme I was added and hydrolyzed for 6 h at 50℃ and pH 7.0.Under these conditions,the degree of hydrolysis of egg white protein reaches 53.09±0.29%,and the free-phenylalanine efficiency reaches85.46±0.73%.Then,on this basis,the adsorption process for phenylalanine was clarified using the removal rate of phenylalanine as main indicator:10%(w/v)No.4 activated carbon was added into the hydrolysate supernatant and adsorbed for 2h at 25℃ and pH 3.0.After adsorption,the phenylalanine content of the obtained low-phenylalanine peptide was reduced to 0.39%,and the protein recovery rate is 28.68%.Previous studies indicate that there are still some high molecular weight peptides in the hydrolysate after two-step hydrolysis.Such peptides are easily to be adsorbed and removed during the adsorption process,causing a large amount of nutrient loss.Therefore,on the basis of the abovementioned two-step enzymatic hydrolysis,neutral protease I enzymatic hydrolysis was added,and the amount of flavor protease I was reduced.The results show that the content of macromolecular peptides and free amino acids in the hydrolysate decreases,while the content of oligopeptides increases.After 9%(w/v)No.4 activated carbon adsorption,the phenylalanine content drops to 0.27%,and the protein recovery rate increases to 31.20%.By studying the effects of activated carbon’s physical and chemical properties,adsorbent properties and solution properties on the adsorption process,the adsorption behavior and mechanism of activated carbon to phenylalanine and different components in the hydrolysate were discussed.It is found that high molecular weight peptides and aromatic amino acids are more likely to be adsorbed on activated carbon.The presence of micropores in activated carbon is more conducive to its adsorption of small molecules,and the presence of mesopores is more conducive to its adsorption of larger molecules.Hydrophobic interaction is the main driving force for the adsorption of phenylalanine on activated carbon,followed by hydrogen bonding and electrostatic interaction.The strength of the hydrogen bond is closely related to the number of acidic groups(such as hydroxyl and carboxyl)on the surface of the activated carbon,while the electrostatic interaction is affected by the pH and ionic strength of the solution.This work provides significant theoretical guidance for the efficient preparation of low-phenylalanine peptides.