Study On Functional Properties Of Casein-Soy Protein Plastein

Plastein is proteinase-induced peptide aggregates.Plastein synthesized by enzymatic methods can increase the biological potency and functional properties of proteins and provide new protein resources.Casein and soy protein are animal proteins and plant proteins with high nutritional value.The plastein reaction can combine casein with soy protein,make up for the deficiency of amino acid pattern and improve the biological activity of them,creating a novel protein product that is both nutritious and biologically active.This paper mainly studied the reaction conditions of synthetic protein combined casein with soybean protein and the functional properties of plastein products.It is hoped that they can combine the advantages of the two proteins and give better functional properties of plastein products.At the same time,the plastein products were characterized.First of all,the hydrolysis conditions of casein and soy protein were optimized.Pepsin was used to hydrolyze casein and soy protein using the degree of hydrolysis as an indicator,respectively.And after single-factor and orthogonal test,the casein hydrolysis conditions were 1.0 kU/g protein,casein concentration 4.0%(w/v),pH 2.0,temperature 39°C and time 4.0 h;the soy protein hydrolysis conditions were 1.5 kU/g protein,soy protein concentration 4.0%(w/v),pH 2.0,temperature 40°C,time 5.0 h.Hydrolysis conditions were optimized to obtain hydrolysates with a degree of hydrolysis of 10.21% and 11.63%.Then,the conditions for synthesizing proteins from casein and soy protein hydrolysates were optimized.The plastein reactions were conducted with pepsin and the two hydrolysates of proteins were mixed using free amino acid reduction as an indicato.The results showed that the reduction of free amino acid reached 190.64 ?mol/g protein under the conditions of substrate concentration 40%(quality ratio 1:1),amount of enzyme 2.5 kU/g protein,pH 5.0,temperature 42°C,and synthesis time 3.0 h.The plastein products were studyed on functional characteristics.The result showed that plastein products have higher bile acid binding capacity than raw protein.And the capacities of protein hydrolysates to bind amounts of sodium cholate,sodium deoxycholate,and sodium cholate were 2.31,2.23,and 3.05 ?mol/100 mg,respectively.At the same time,plastein products can improve the antioxidant capacity comparing with raw protein and protein hydrolysates.Compared with the hydrolysates,the DPPH radical scavenging rate increased by more than 1.3 times,the reducing power increased by more than 1.5 times,and the hydroxyl radical scavenging rate increased by nearly 2 times.Changes in these functional properties are related to hydrophobic amino acids.Finally,The plastein products were characterized by electrophoresis,infrared spectroscopy,fluorescence spectroscopy and mass spectrometry.The results showed that the plastein product is a novel macromolecular protein obtained by combining casein with soy protein.Compared with the raw protein and their hydrolysates,the secondary structure changed with intramolecular or intermolecular hydrogen bonding,and the hydrophobicity of the surface was significantly enhanced,indicating that the plastein synthesis involved the participation of hydrophobic interaction and hydrogen bonding.