Self-assembled Of Amphiphilic Egg Yolk Peptide And Its Functional Application Research In Food Colloid

Food grade colloidal particles have shown great advantages in the preparation and stabilization of interface-dominant multi-phased food systems,such as emulsions and foams.Currently,in the food industry,it is committed to finding and designing of some food protein(peptide)-based particles to improve the functional properties of foods via control of interface in food systems.However,the study regarding using natural food-grade peptide-based particles to achieve these still is less.In the present study,the amphiphilic yolk peptide,which can self-assemble into micellar nanoparticles in aqueous solutions(here called EYPNs),was obtained from the by-product of industrial extraction of egg yolk phospholipids and yolk oil(defatted egg yolk powder)by treating with trypsin.EYPNs exhibits excellent interfacial activity at the oil/water interface and enable the production of relatively stable Pickering nanoemulsions,Pickering foam,gel beads and food colloidal systems.The main conclusions are as follows:(1)EYPNs as a nano-carrier to improve the water solubility and bioaccessibility of hydrophobic active substances were evaluated.Firstly,the micellar mechanism of EYP was studied and the self-assembled structure of EYP was characterized.EYP self-assembled into micelle nanoparticles via hydrophobic interaction,it formed spherical particle had an average size of about 25 nm.By a fluorescence probe method,the determined critical micellization concentration was about 0.1 mg/m L.Next,based on the p H-response of EYPNs,we designed a colloidal delivery system to load hydrophobic active substances.After dissociating EYPNs by adjusting p H to 12,curcumin(Cur),a model of the hydrophobic active substance,was mixed with EYP,followed by adjusting p H to 7.Cur was embedded inside the reassembled EYPNs by the hydrophobic interaction,resulting in stable EYPNs-Cur composite nanoparticles.Compared to the free,the embedment significantly increased the solubility of Cur(nearly 3341 times),and the embed Cur almost did not degrade after storage for a month.After in vitro simulated digestion,the retention of Cur from the composite nanoparticles was nearly twice as much as the free Cur,suggesting that EYPNs can be used as a nano-carrier for stabilizing the hydrophobic active substances and improving their bioavailability.(2)The adsorption characteristics and structure of EYPNs at the air-water interface werestudied based on the stabilized food grade Pickering foam.Firstly,the influence of p H on the morphology and air-water interface characteristics of EYPNs and stabilized foam by EYPNs were studied.The results showed that the charge of EYPNs decreased with the reduction of p H,and the morphology of EYPNs changed from micelles to large-scale aggregates.The air-water interfacial tension decreased with the decrease of p H,whereas the contact angle increased with the decrease of p H.However,when the value was less than 90°,the salt ions had no significant effect on the air-water interfacial activity of EYPNs.When the p H was6.0-9.0,EYPNs were distributed in the foam channel and the air-water interface.The coulomb repulsion between EYPNs decreased,resulting in the particle aggregation,which may be explained by that the foam liquid membrane at the air-water interface enhanced the stability of the foam with the decrease of p H(4.0-2.0).These results suggest that EYPNs have good foam formation ability and foam stability at a p H-dependent manner.The Pickering foam prepared at p H 3.0 showed the best performance.(3)The oil-water interface assembly and interface structure of EYPNs were studied.Food-grade Pickering nanoemulsion with a diameter of less than 200 nm was prepared and stabilized by EYPNs.The results showed that EYPNs,as natural peptide-based nanoparticles,had many advantages in stabilizing the oil-water interface,including small particle size,moderate wettability,high interfacial activity and structural deformability after adsorbed on the oil-water interface,which could stabilize Pickering nanoemulsions with an average particle size of less than 200 nm and a polydispersity index below 0.2.The nanoemulsion particle size could be effectively controlled by high pressure microfluidics parameters and oil phase ratio.Meanwhile,the change of oil phase type and polarity did not affect the formation and stability of nanoemulsions.When the oil phase was edible vegetable oil,the Pickering nanoemulsions were a food grade property as a whole.The stability tests showed that these Pickering nanoemulsions could effectively resist Ostwald ripening,showing a long-term storage stability that could be used as the stable precursor templates to spray structured oil powder by spray drying.The excellent stability was mainly attributed to the close and irreversible interfacial adsorption layer formed by the intact EYPNs on the interface of the emulsion droplets.The natural amphiphilic yolk peptide and its self-assembly behavior could be used to design and construct a new type of nano Pickering emulsifier.The stabilizedPickering nanoemulsions with food grade had a wide range of sustainable application potential in food,medicine and cosmetics.(4)A single droplet dispersing gel method was employed to compound EYPNs stabilized Pickering alginate oil nanoemulsions with sodium alginate calcium gel system,which was to prepare the functional microspheres loaded with alginate oil nanoemulsions.The results showed that the composite system rheological properties,nanoemulsion encapsulation efficiency,thickness,hardness,spherical factor,surface roughness and stability of the composite gel beads could be controlled by sodium alginate concentration.The composite gel beads solid content was inversely proportional to the concentration of sodium alginate.This was mainly due to the loss of water and nanoemulsions during the formation of gel beads in the low concentration alginate composite system,which was much larger than that of crosslinked calcium ions.Both sodium alginate and EYPNs had antioxidative activity,and the composite gel microbead network inhibited the material exchange at the oil-water interface and retarded the contact between the nanoemulsions and the outside air,thereby reducing the oxidation rate of alginate oil.