Production Of Nanoliposomes Loaded With Walnut Protein Hydrolysates:Structure And Stability

In this study,the walnut degreasing powder was used as raw material to prepare peptides by alkaline protease and complex enzyme including amylase,cellulase and pectinase,and the structure and functional properties of the peptide were determined.Besides,nano liposomes loaded with walnut peptides were prepared by membrane dispersion method.The structure characteristics and stability of liposomes were investigated.Finally,peptides and liposomes were applied to edible gels to investigate their effects on the texture and rheological properties.The study has guiding significance for the further development and utilization of walnut resources,which is expected to improve the stability of walnut polypeptide,overcome the defects of polypeptide in food application,and expand the application of walnut polypeptide in food field.The main research contents and results were as follows.（1）Walnut peptides are rich in amino acids.Glutamic acid（21.4%）,threonine（17.0%）,arginine（15.5%）,leucine（6.7%）,proline（5.8%）,aspartic acid（5.3%）and glycine（4.7%）were the main amino acids of walnut peptides.The surface hydrophobicity of 5-10 k Da peptides was the highest,while that of crude peptides was the lowest.Walnut peptides had smooth surface,massive structure,small particle size in aqueous solution,and the system was stable and not easy to aggregate.The lower the molecular weight of walnut peptide,the higher the antioxidant activity.（2）The particle size and PDI of liposomes increased significantly,while PDI was always less than 0.3,indicating that liposomes were stably distributed in the aqueous phase.Through microscope,it is found that the liposomes uniformly dispersed in the water phase.The high concentration may result in the aggregation of liposomes and larger particle size.The FTIR showed that the peptides were wrapped in the polar part of the phospholipid membrane and combined with PO^2-by hydrogen bond.（3）After 20 days storage in 4^oC and 25^oC,the particle size of liposomes increased significantly,and the entrapment efficiency of liposomes was 43.3-46.2%and 38.3-41.0%,respectively.Under the condition of higher temperature storage,the particle size of liposome was larger and the leakage rate of peptide was higher.The particle size of lyophilized liposomes was larger than that before lyophilization.After 4 days of frozen storage,the particle size of liposomes increased and the encapsulation efficiency decreased significantly.When the digestion time reached 2 hours,the release rate of liposomes in the simulated intestinal tract was 83.3%,while only 38.4%in the simulated gastric tract.（4）After adding peptides and liposomes,the hardness and elasticity of the gel gradually increased.The effect of adding liposomes on gel hardness was slightly larger than that of adding the same number of peptides.No matter adding peptides or liposomes,the effect on the cohesion of gel was not obvious.The viscosity of the gel increased with the increase of peptides or liposomes addition.The G′and G″of edible gels increased with increasing frequency.In the whole frequency scanning test,the storage modulus（G′）was always greater than the loss modulus（G″）.The samples formed a higher gel aggregation network structure.