| With an increasing emphasis on naturalness and safety of foods,much more attention has been attracted to the natural plant essential oils with unique aromatic properties.However,the flavor active ingredients in plant essential oils have strong volatility,poor stability and easy oxidative degradation,which limit the wide application in functional 3D-printed products with individualized flavor.Pickering emulsions（PEs）,as carriers for the encapsulation and protection of active ingredients,have the advantages of high loading,excellent stability,and solid-like structure,which provide new ideas to solve the above problems.Therefore,in this study,pea protein isolate（PPI）-high methoxy pectin（HMP）-epigallocatechin gallate（EGCG）complexes were used to construct PEs and high internal phase Pickering emulsions（HIPPEs）.The formation and stability mechanisms of PEs and HIPPEs and environmental tolerance mechanisms were elucidated by regulating the interface behavior.On this basis,cinnamaldehyde and eugenol wers used as the typical volatile flavor to explore the mechanism of effective encapsulation and stabilization of Pickering emulsions.PEs and HIPPEs loaded with flavor active ingredients were used as 3D printing inks,revealing the relationship between the rheological properties of Pickering emulsions.The purpose of the current work is to provide theoretical guidance and technical support for broadening the adaptability of emulsion-based flavor ingredients in food processing.The PPI-HMP-EGCG complexes were prepared and used to stabilize PEs and HIPPEs,and the effect of interfacial properties on the rheological behavior and stability of emulsions was investigated.By comparing the difference in the interfacial wettability of the complexes formed by PPI and HMP,it was found that when the p H was 3.5 and the mass ratio of PPI and HMP was 1:1,the three-phase contact angle of the complexes reached 77.8±0.2°,which effectively enhanced the hydrophobicity of PPI.The effects of different EGCG ratios on the complexe properties were investigated by the interfacial wettability,interfacial shear rheology,and interfacial tension.It was found that when the mass ratio of PPI to EGCG was 30:1,the average particle size of the PPI-HMP-EGCG complex was 286.6±1.7 nm and poly-dispersity index was 0.30±0.01,and a uniformly distributed regular spherical structure was formed.The significant improved partial wettability（81.6±0.4°）,the highest interfacial viscoelastic modulus and the lowest interfacial tension（4.18±0.02 m N/m）were obtained in the complex.The interaction between the complexes was investigated by the Fourier transform infrared spectroscopy,and the hydrogen bonding and hydrophobic interaction were confirmed in the PPI-HMP-EGCG complexes.PEs（oil-phase volume fraction from 52%to 72%）and HIPPEs（oil phase volume fraction up to 83%）were prepared using different concentrations（ranging from 1.0 mg/m L to 20 mg/m L）of PPI-HMP-EGCG complex as Pickering stabilizers.The interfacial microstructure showed that the oil droplets were surrounded by a viscoelastic particle-based interfacial layer formed by the PPI-HMP-EGCG complexes,and the continuous phase was filled with a network formed by HMP.The bulk rheological results further indicated that the formation of elastic gel-like network structures also endowed PEs（low particle concentration of 1.0 mg/m L）and HIPPEs（high oil-phase volume fraction of 83%）excellent storage（remained stable after storage at 25°C for 30 days）and physical stability（the instability index?0.16±0.01）.The results of Pearson correlation analysis demonstrated that the interfacial properties,such as interfacial viscoelasticity and interfacial microstructure of emulsions,were positively correlated with the macroscopic properties,such as bulk rheology and stability,at different particle concentrations or oil phase volumes.In order to further clarify the environmental tolerance of Pickering emulsions,the physical stability and chemical stability of oil phase in the system at different p H（2～9）and ionic strength（Na Cl 0～1000 mmol/L）were investigated.The environmental tolerance mechanisms of PEs（oil-phase volume fraction of 52%）and HIPPEs（oil-phase volume fraction of 83%）were also elucidated from the perspective of interface characteristics.The results showed that the physical barrier formed by the dense high-viscoelastic particle-based interfacial layer,in concert with the strong gel-like network structure and high viscosity,effectively blocked the contact between the oil phase and the pro-oxidant and prevented the aggregation of oil droplets,allowing to the best physical（instability index<0.05±0.003）and oxidation stabilities（lipid peroxide concentration<22.04±0.88μmol/g after 15-days storage at 45°C in the dark）of PEs and HIPPEs at p H 3.5 or 0 mmol/L Na Cl.Compared with PEs and HIPPEs at p H 3.5 or 0 mmol/L Na Cl,under neutral and alkaline conditions（p H 7 and p H 9）,the physical and oxidative stabilities of PEs and HIPPEs were reduced,which was ascribed to formation of weakly viscoelastic responsive interfacial layers due to the insufficient number of complexes,the oil droplets could not be fully encapsulated,and the apparent viscosity and the gel-like network structure strength were reduced accordingly.However,due to the frequency dependence of weak interfacial layers that were not easily converted,PEs and HIPPEs did not stratify after storage.At high ionic strength（≤1000 mmol/L Na Cl）,particles aggregated at the interface,and the weak interfacial layer had poor encapsulation of oil droplets and could not prevent the oil phase from contacting the pro-oxidant,resulting in the reduction of oxidation stability.Simultaneously,the particles that were not adsorbed to the interface and fall off to the continuous phase combined with HMP enhanced the viscosity and rigidity of the system,so that PEs and HIPPEs did not appear stratification after storage.Under the conditions of different oil phase compositions,cinnamaldehyde and eugenol were used as the active ingredients of typical flavor essential oils,and PEs and HIPPEs stabilized by PP-HMP-EGCG complexes were used to encapsulate flavor ingredients.Based on the viscoelasticity of the interfacial layer,interactions between the particles on the interface and flavor components in the oil phase,the changes of interfacial microstructure and water distribution,the encapsulation and stabilization mechanisms of cinnamaldehyde and eugenol in PEs and HIPPEs were investigated.Raman spectra showed that with the incorporation of cinnamaldehyde in the oil phase,the carbonyl group(C=O,1660 cm-1)disappeared and the imine group(C=N,1630 cm-1)formed,indicating that the Schiff base reaction occurred between the aldehyde group of cinnamaldehyde and the free amino group of the complex at the interface.This reaction promoted the adsorption of more particles to the interface,which was beneficial to the formation of an elastic interface layer that completely coated oil droplets,thus improving the retention rate of cinnamaldehyde.In contrast,when eugenol was added to the oil phase,the hydrogen bonding between the hydroxyl groups of eugenol and the hydroxyl groups of proteins led to the aggregation of particles at the interface,forming a weak interface layer dominated by viscosity and could not completely cover the oil droplets,and the fluorescence intensity of the interface was also reduced by 23%-32%.Thus,the cinnamaldehyde-loaded PEs and HIPPEs had better storage stability than the eugenol-loaded PEs and HIPPEs,and the retention rate was also improved by about 15%～20%.The addition of tea camellia seed oil in the oil phase decreased the effective oil density,enhanced the apparent viscosity and elastic gel-like network structure of the emulsion,inhibited the mobility of immobilized water,and improved the retention rates of cinnamaldehyde and eugenol by approximately 6%and 12%after storage at 25°C for 30 days.In order to clarify the adaptability of Pickering emulsions embedded with volatile flavor components in 3D printing,PEs and HIPPEs loaded with different proportions of cinnamaldehyde（0%,25%,50%,75%and 100%）were used as printing inks,and the effect of the ratios of cinnamaldehyde in the oil phase on the bulk/interfacial rheological properties,printing accuracy,textural properties and release rate during printing were investigated.The bulk rheological results showed that PEs containting 0%～25%cinnamaldehyde and HIPPEs containing 0%～75%cinnamaldehyde exhibited solid-like viscoelastic responses with high storage modulus and suitable appropriate viscosity,which provided extrusion properties and supporting properties for emulsion-based inks.The differences among the PEs-printed cuboids,cylinders and turtles models showed that the distinct structural collapse and profile loss of models occurred when the cinnamaldehyde proportion was over 25%.However,for HIPPEs with the cinnamaldehyde proportion up to 75%,the printed models still had excellent printing performance,gel strength,and texture properties with smooth surface,regular shape,and high than 93%printing accuracy.Additionally,the solid-like interface layer and elastic gel-like network structure of the emulsion enhanced the resistance of the printed object during the extrusion process,improved the printing stability,and slowed down the release of volatile flavor substances during the 3D printing,so that the release rate of cinnamaldehyde in PEs and HIPPEs based ink was controlled within 10.02±0.01%and 11.29±0.01%,respectively.Pearson correlation analysis showed that the printing accuracy of PEs/HIPPEs-based ink was significantly positively correlated with the bulk rheological behavior and post-printing texture properties（hardness,springiness,cohesiveness,and gumminess）,and negatively correlated with interface viscoelasticity. |
PDF Full Text Request