Study On The Construction Of Multi-phase Structured Oils Based On Monoglycerides And Tea Saponins

Traditional processing processes,such as extraction,transesterification,hydrogenation,or the above combined modification of special fats for food industry,result in a large amount of saturated and even trans fatty acids,which may pose health risks.Therefore,the development of green,safe,healthy and stable novel structured oils through different strategies has become a concern in the food industry in recent years.In this study,the combination of interface self-assemble behaviors of natural small molecule tea saponin(TS)and the adsorption of monoglyceride(MAG)crystals was used to construct multi-phase structural oils(oleofoams,emulsion gels and emulsion foams),and their properties were systematically characterized.Besides,the relations among the continuous phase,interface behaviors and macroscopic functional characteristics were discussed,which provided theoretical guidance and technical support for the development of novel structured oil-based products with non-hydrogenated,zero-trans and low-saturated fatty acids.The main research results of this paper are as follows:(1)The influence of MAG concentrations on the microstructure and macroscopic properties of oleofoams were studied,and the evolution of properties and stabilization mechanism for oleofoams during whipping was mainly investigated.It was found that oleofoams with certain mechanical strength(G’=10~4Pa),good thermal stability and high overrun(nearly 190%)could be formed even at a concentration of 3 wt%MAG.The stability of oleofoams mainly dependent on the irreversible adsorption of MAG crystals as Pickering particles around bubbles to excert an interface effect.Additionly,the performance and foaming ability were significantly improved with the increase of MAG concentrations.The shear-induced partial aggregation of interfacial crystals at the early stage of whipping helped to form a firm foam structure,which ensured oleofoams with fine,smooth texture and good mechanical properties.However,excessive whipping would lead to crystal bridging between adjacent bubbles,resuled in partial destruction of the crystal adsorption layer.The merger and the rupture of bubbles,which caused a decrease in the overrun,an increase in bubble size,and a decrease in the foam appearance quality.(2)Based on the interfacial self-assembly of tea saponins(TS)and the adsorption of MAG crystals,TS-MAG emulsion/emulsion gels were obtained,and were systematically characterized by different nano-micro scale methods combined with spectroscopy.The results showed that the system exhibited an interesting MAG concentration-dependent behavior.When appropriate amount of MAG(1 wt%-3 wt%)was applied,emulsion gels possessed significantly improved emulsification ability,and droplets size was smaller,the gel network structure was denser,thereby had higher mechanical strength(G’up to 10~4Pa),good thixotropic recovery(70-90%)and thermal response ability.This was attributed to the synergistic co-existence and interaction(mianly hydrogen bonding force)between the TS fiber and MAG crystals at this time,that was,the combination of interfacial tension reduction and the effect of gelation enhancement for the oil phase.At higher MAG concentrations(4wt%-5 wt%),there was a competitive adsorption between TS and MAG at the interface,and the oil-water interface began to be dominated by MAG crystalline particles,resulted in the weaker elastic interface,as well as the significantly declined appearance quality and stability of subsequent formed systems.(3)The application characteristics for oleogels and oleofoams constructed in frozen aerated emulsions were explored and evaluated.The results showed that the part of replacement of oleogels to palm oil could obtain the solid network structure,which furtuer provided the ideal overrun(45%),hardness(750 g)and melting properties of the frozen aerated emulsion.The emulsion prepared with the total replacement of oleogels also poccessed certain mechanical strength and storage stability.However,the overall properties of the frozen aerated emulsion obtained were reduced.The quality and performance of samples were not ideal when only the oleofoam was used.Excessive partial coalescence(coalescence rate was 83%)resulted in the lack of interaction between the fat globules and with the bubble interface,which could not effectively build the firm structure based on the cross-linked fat globules.Further,air bubbles could not be introduced and stabilized effectively,further caused the low overrun(17%),large and irregular ice crystals and the poor melting performance for the system.(4)Emulsion foams with different oil phase contents were prepared with TS(1wt%)-MAG(1 wt%),and the stability and application characteristic were further evaluated.The study showed that with the decrease of the oil content,the foaming ability of emulsion gels increased,meanwhile,the foam stability decreased.At high oil contents(60 wt%and 75wt%),TS-MAG based emulsion foams were stiff,creamy,and had a certain yield stress(G’was about 103 Pa),besides,they poccessed good foam stability.When oil contents were low,bubbles were prone to break and coarsened during storage because they could not be effectively protected.All of these could be explained as the foam stability mainly depended on the tight accumulation of oil droplets at the interface to form a strong and thick layer.Therefore,the strength and stability of emulsion foams could be adjusted by the filling density of oil droplets.