| Increasing attention have been fouce on the all-natural and clean label ingredients.Natural Quillaja saponins(QS)can self-assemble to form a fiber network film inducted by the oil-water interface.Recently,both high internal phase emulsion gels(HIPEG)and oleogels were popular in development of zero-trans,low-saturation fats used in the foods.Herein,the assembly behavior of QS at the oil-water interface was adjusted(e.g.,the water and oil phase microenvironment,the emulsion droplet size,the ratio of saponin to oil,and so on)to fabricate HIPEG and then Oleogels based on a emulsion template.Their structural properties were systematically characterized to reveal the internal relation and regulation mechanism between the self-assembly behavior of QS at oil-water interface and the construction of emulsion gels and oleogels,and provide theoretical guidance for the development of new health food special oils.The main conclusions as follows:(1)The effect of ionic strength and type on the self-assembly behavior of QS at the water phase and oil-water interface and its influence on the construction of HIPEG and oleogels were explored.The negative charges of QS were shielded by ions,that enhanced its ability to form micelles in the water phase.QS micelles were attracted to the oil-water interface and self-assembly formed fibrous film,and the higher the ionic strength and negative ion charge,the denser the interface film,however the positive ion charge was just opposite.The ions promoted the interaction among droplets and enhanced the viscosity,mechanical strength and structural recovery ability of the emulsion gels.The oleogels prepared by the emulsion template strategy had a stronger mechanical than the emulsion precursors,but the ions weaken its strength.(2)Increasing p H led to a change in the charge of the hydrophilic head of QS,that promoted the adsorption of QS micelles onto the oil-water interface and strengthened the interface self-assembly films.Compared to low p H,HIPEG constructed at high p H had smaller droplet size and stronger electrostatic interaction among the droplets,exhibiting high viscosity,mechanical strength and structure resilience.Based on the interface assembly,the oleogels had strong mechanical properties(G’up to 10~5Pa).It should be noted that the emulsion gels had a strong gel structure at p H 1;however,oil leakage was occured during the dehydration process.Temperature had no significant effect on the self-assembly behavior of QS at oil-water interface as well as the microstructure and mechanical strength of the resulted both HIPEG and oleogels.(3)The self-assembly behavior of QS at oil-water interface was further investigated by adjusting oil phase microenvironment(e.g.,investigating vegetable oils of different polarities and free fatty acids)to control the fabrication of HIPEG and oleogels.The results showed that the lipid companions of oils weakened the diffusion of QS onto the oil-water interface,resulted in a larger droplet size,lower viscosity,mechanical strength and resistance to external forces,which in turn led to weak oleogels.The adsorption of QS at oil-water interface was increased with increasing of the carbon chain lengths and decreasing of unsaturation degrees based on the different activities of FFA.Due to the interaction between FFA and QS at the interface,the increasing of carbon chain lengths can enhance the viscosity,gel network strength and resistance to external forces of emulsion gels.Furthermore,the higher content of FFA,the greater the effect,and the influence of saturated acid was much stronger unsaturated acid.On the contrary,oleogels strength showed a decreasing trend with the increasing of FFA carbon chain.Therefore,the physical properties of HIPEG and oleogels can also be controlled by adjusting oil phase.(4)Emulsion droplet size and saponin loading on the dynamic viscosity,small deformation oscillation rheology and microstructure of HIPEG and oleogels were also evaluated.The results shown that both the emulsion gels and oleogels were fabricated by a non-covalent physical crosslink among oil droplets,and exhibited a shear-thinning behavior.With the emulsion droplets decreasing,the tightly dispersed oils were fabricated,resulting in a stronger network structure with high viscoelasticity of both emulsion gels and oleogels.Meanwhile,the strength of emulsion gels and oleogels had also a dependence on the QS concentration,where the emulsion droplet size decreases within critical concentration(1.5%)due to the electrostatic repulsion between the oil droplets,giving the emulsion gels stronger viscoelasticity and gel strength.Subsequently,increasing QS concentration above 1.5%,the free QS molecules are attributed to the formation of a stronger gel strength of HIPEG.However,the oleogel strength was enhanced by the decreasing of emulsion droplet size and the increasing of QS concentration.Therefore,the controllable construction of the HIPEG and its template oleogels can be achieved by adjusting the emulsion droplets size and the biosurfactants concentration,and the zero-trans,low-saturation new food-specific oils and functional active substance delivery vehicle can be developed in a targeted manner. |
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