| Egg white protein(EWP)is a kind nutritious protein with wide range of sources.However,few studies investigated the emulsifying and delivery properties of EWP,even it behaved good interface adsorption properties.This paper focused on the emulsifying and aggregation behaviors of egg white protein to develop the application of egg white protein in emulsion system and bio-active ingredient delivery.The specific results are listed as follows:Firstly,the influence of acid or moderate heat treatments on physicochemical characteristics,structure and emulsifying capacity of EWP after re-adjusted to various pH was investigated.Simultaneously,the stability of the emulsions prepared with acid and acid-heat induced EWP(AEP and AHEP)was tested by measuring particle diameter and microstructure of the droplets after salt(0-200 mM NaCl)and heat(90 ?,30 min)treatments at pH 3.0-4.2.The results revealed that the emulsifying capacity of EWP was enhanced after acid or acid-heat treatment with more hydrophobic amino acids and charged groups exposed on the surface,but little changes in second structure.Proteins adsorbed at the oil-water interface were mainly ovotransferrin and ovalbumin.The emulsions made with AEP and AHEP were stable for 3 weeks without phase separation at pH below isoelectric point(pI?5.0),but exhibited some aggregation at pH near or above pI.The heat stability of emulsions depended on pH and thermal history.The emulsions made with AHEP performed better heat stability than AEP-stabilized emulsions.The salt stability of emulsions depended on the net charge.At pH 3.0,the emulsions were stable in the presence of<100 mM NaCl with no changes in particle size.At other pH,the emulsions showed good tolerance to 50 mM NaCl.These results have important implications for the formulation and production of emulsion based acid products,using egg white protein as emulsifier.Secondly,we investigated the effect of enzyme on characteristics of egg white protein(EWP)and synergistic efficiency of pectin addition on properties(thermal stability,salt resistance and antioxidant activity)of emulsions stabilized by original or hydrolyzed EWP.The EWP solutions were incubated at pH 7.0,under 50? for 2 h,with various amount of enzyme added in.With enzyme concentration increased,more ovotransferrin and ovalbumin were hydrolyzed,and more hydrophobic amino acids exposed to polar environment,especially tyrosine.In addition,the DPPH and ABTS radical scavenging activity of EWP increased with enzyme dosage increasing.Pectin addition can effectively stabilize the droplets distribution with small effective diameter and polydispersity index.In comparison,the emulsions stabilized by hydrolyzed EWP with 0.3%pectin behaved better thermal and salt tolerant stability,while with poorer antioxidant capacity attributed to weaker intermolecular interactions.The rheological measurement showed that the viscosity of hydrolyzed EWP stabilized emulsion was relatively lower and G' was more dependent on frequency,indicating weaker cross-links among droplets.The results may provide theoretical guidance for application of enzymatic and polysaccharide blends in improving protein functionality.Thirdly,the potential of egg white protein(EWP)to be developed into a kind of Pickering stabilizer for oil-in-water emulsions was investigated.The EWP microparticles were formed by heating at 90 ? for 45 min,followed by homogenization under low pressure.The characteristics and micro structure of microparticles prepared under various pH(3.0,3.8)and protein concentration(2-10%)were tested.Simultaneously,the properties of Pickering emulsions integrated by EWP microparticles,with fibrous or granular morphology,were investigated.At pH 3.0,the particles may transfer from fibrous structure to granular structure with protein concentration increased or salt addition.At pH 3.8,granular microparticles were formed under various protein concentrations.The structure of EWP microparticles were mainly maintained by hydrophobic interactions and hydrogen bondings.The granular particles showed higher surface loading of protein and viscoelastic moduli in the integrated Pickering emulsions.These results have important implications for the formulation and production of emulsion based semi-solid products,using egg white protein as emulsifier and fat substitute.Fourthly,we investigated the encapsulation of curcumin into egg white protein(EWP)microparticles.Processing conditions used to formulate the microparticles,including pH and the addition of ethanol,were used to control the unfolding and aggregation behavior of EWP.The curcumin loading capacity of the EWP microparticles was found to be strongly linked to the structural transitions of the protein during heat denaturation,and the microscopic properties of the particles such as particle size and surface hydrophobicity.Fibrous particles were formed at lower pH(3.0)and were associated with a higher curcumin loading than the granular particles formed at pH 3.8.Addition of ethanol,which leads to an increase in ?-sheet structure,and the formation of a coarser gel structure during heat denaturation,resulted in an increase in particle diameter and a decrease in the loading capacity.The highest loading capacities were 11.53 and 9.89 mg/g protein,at pH 3.0 and 3.8,respectively.Encapsulation in EWPmicroparticles was shown to both effectively slow the degradation rate and protect the antioxidant activity of encapsulated curcumin.Finally,the efficiency of egg white protein microparticle(EWPM)and pectin sol(PS)addition in blocking flow behavior of light mayonnaise was investigated in this study.The texture properties,color,micro structure and thermal resistance were also measured for better understanding of synergistic effect of EWPM and PS on characteristics of light mayonnaise.At ratio of 2:4(in weight ratio of PS and EWPM),the sample showed higher viscosity and hardness,attributed to the formation of larger protein aggregates induced by repulsion between protein and pectin molecule.The speculation was verified through the micro structure of mayonnaise samples observed by laser light confocal microscope.With the amount of EWPM increased,the yellow value of light mayonnaise increased,but thermal resistance decreased.For EWPM-rich samples,moderate heat treatment can strengthen the interaction between particles,inducing the increase of viscosity. |
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