Preparation Of Pea Peptides By Ultrasound-Regulated Enzymatic Method And Its Self-Assembly Characteristics

The annual output of peas in China is rich,and pea protein（PP）has good nutritional value and low allergenicity,so it is widely concerned by researchers.However,due to the functional properties of pea protein are easily affected by processing conditions,enzymatic modification of pea protein is often used to improve its functional properties and utilization value.Therefore,in this study,pea protein was used as raw material to study the effect of ultrasound-regulated enzymatic hydrolysis on the emulsifying properties and antioxidant activity of pea peptides.Combined with the effect of ultrasound field environment on protease activity and structure,the process conditions of ultrasound-regulated enzymatic preparation of pea peptides were optimized.The effects of ultrasound on the self-assembly characteristics of pea peptides were investigated by studying the structural characterization of pea peptides and their spontaneous and triggered self-assembly behaviors in solution.At the same time,the relationship between the self-assembly characteristics and emulsifying properties of pea peptides was studied in order to develop a stable peptide-based emulsion system and provide a theoretical basis for the application of pea protein in the food industry.（1）The effects of ultrasound parameters on the activity and structure of Alcalase were studied,and the process conditions for the preparation of pea peptides by the ultrasound-regulated enzymatic method were optimized.The results showed that the activity of Alcalase increased by 22.09%under ultrasound.Ultrasound could increase the enzymatic reaction rate constant of Alcalase.Ultrasound treatment made the structure of Alcalase more regular and flexible,exposed more active sites,and promoted the enzymatic reaction.The optimal conditions for the preparation of pea peptides by the ultrasound-regulated enzymatic method were as follows:ultrasound power density 2.71 W/cm³,time 25 min and temperature45℃,and the degree of hydrolysis of pea protein was 18.61%.Pea peptides had good emulsifying activity and antioxidant activity.（2）The structural characteristics and self-assembly behaviors of pea peptides（UPPH）prepared by ultrasound-regulated enzymatic hydrolysis and pea peptides（PPH）prepared by conventional enzymatic hydrolysis were studied.The results showed that the molecular components of UPPH and PPH were concentrated below 3 k Da,and the content of<3 k Da peptides in UPPH was significantly higher than that in PPH.Amino acid sequence analysis showed that the proportion of peptide molecules with hydrophobic amino acids at both ends of UPPH was higher than that in PPH.The results of fourier transform ioncyclotron resonance（FTIR）and endogenous fluorescence spectroscopy showed that the content ofβ-sheet and surface tryptophan in UPPH was higher than that in PPH.The critical micelle concentration（CMC）of UPPH was lower than that of PPH,and UPPH was more amphiphilic.Driven by concentration and p H,UPPH and PPH underwent self-assembly dissociation or association.Compared with p H7 and p H9,UPPH self-assembled into larger spherical particles at p H4,the content ofβ-sheet increased and the fluorescence intensity decreased.At p H4,PPH formed self-assembled aggregates in the form of monomer stacking,the content ofβ-sheet increased and the fluorescence intensity decreased.（3）The relationship between self-assembly and emulsifying properties of pea peptides driven by p H was studied.The results showed that compared with p H2-6,the emulsifying activity and emulsion stability of UPPH and PPH were better at p H7-9,and under this condition,the emulsion droplets stabilized by UPPH and PPH were smaller,the viscosity was lower,and the system was stable.Both UPPH and PPH formed a self-assembled solution with relatively low viscosity and a small contact angle(θ_aw)at p H7.Theθ_aw of UPPH self-assembly was greater than that of PPH self-assembly at p H4,p H7 and p H9.The dynamic interfacial adsorption kinetic analysis results showed that the diffusion rate constants(K_diff)of the self-assemblies formed by UPPH and PPH were larger at p H4 and p H9,and the first-order rearrangement rate constant（K_R）of UPPH self-assembly was larger at p H7.At p H7,the self-assemblies formed by UPPH and PPH could be stably adsorbed at the oil-water interface and uniformly and orderly arranged on the droplet surface due to the advantages of small particle size and flexible conformation,and the stability of UPPH emulsions and PPH emulsions was better under this condition.The results of the study provided some theoretical guidance for expanding the application of pea protein in the food industry.