Study On Structure And Properties Of Tween-Wax Composite Oleogels

A series of Tween-wax composite oleogels were prepared by using high oleic acid sunflower oil as base oil,waxes(carnauba wax,rice bran wax,beeswax)and Tween(Tween 20,Tween 40,Tween 60,Tween 65,Tween 80 and Tween 85)as oleogelators.The crystallization characteristics,micro-morphology,physical properties and oxidation stability of oleogels were studied.The purpose of this paper is to provide a theoretical basis for the follow-up research on the performance improvement and application of wax-based oleogels.Firstly,the thermal properties,solid fat content and crystallization kinetics of these oleogels were studied.The results of thermal properties studied by DSC showed that the process of melting and crystallization were affected by the types of Tweens and waxes and the ratios between them.In the melting process,all the oleogels have a large endothermic peak;in the process of crystallization,carnauba wax-Tween oleogels has 2-3 crystallization peaks,rice bran wax-Tween oleogels has only one crystal peak,and beeswax-Tween oleogels has 2 peaks.The results of SFC of these oleogels showed that the SFCs of oleogels decreased with wax ratio decreasing.The melting range of carnauba wax-Tween oleogels and rice bran wax-Tween oleogels were wider than those of beeswax-Tween oleogels.The results of isothermal crystallization kinetics showed that the crystal nucleation mode of oleogels was affected by temperature,the type of Tween and wax and the ratio between them.The crystals of carnauba wax / rice bran wax-Tween oleogels mainly grow in one-dimensional and two-dimensional mixed modes in the range of20?-50?.The mode of beeswax-Tween crystal nucleation was greatly affected by Tween-wax ratio,including one-dimensional and two-dimensional mixed mode growth,two-dimensional and three-dimensional mixed mode growth.The crystallization rate k value was related to the crystallization temperature,the type of Tween and wax and the ratio between them.At the same ratio,the crystallization rate k decreased with the increase of temperature.In the system of carnauba wax / rice bran wax-Tween oleogels,increasing the Tween ratio at 20? could accelerate the crystallization rate of the oleogels,and decreasing the ratio of carnauba wax to rice bran wax will slow down the crystallization rate of the oleogels at 30?-50?.In the beeswax-Tween oleogels system,at the same temperature,increasing the ratio of Tween 20 could accelerate the crystallization rate of the oleogels at 10?,and decreasing the ratio of beeswax would lead to the decrease of the crystallization rate of the oleogels at 20?-40?.In the beeswax-Tween40 /60 /65 /80 /85 oleogels system,decreasing the beeswax ratio in the range of 10?-40? would lead to the slow crystallization rate of the oleogels.Secondly,the microstructure and morphology of Tween-wax composite oleogels was investigated by X-ray diffraction and polarizing light microscope analysis.The results of X-ray diffraction analysis showed that carnauba wax-Tween oleogels has two obvious sharp diffraction peaks at the wide-angle crystal plane spacing d=4.14? and d=3.73?,while the beeswax-Tween oleogels has two obvious diffraction peaks at d=4.16? and d=3.75?.The rice bran wax-Tween oleogels have a small peak in the small angle region d=24.50?,and there are two obvious sharp diffraction peaks in the wide-angle region at d=4.15? and d=3.74?.Diffraction peak intensity of oelogels in wide-angle refion were affected by the types of wax and Tween and the ratio between them.When carnauba wax:Tween 65=9.5:0.5 and beeswax: Tween 65=9.5:0.5 or 9:1,the diffraction peak intensity of oleogels was significantly higher than that of carnauba wax / beeswax oleogels,indicating that the order of oleogels molecules was obviously enhanced,and the diffraction peak intensity of other oleogels was lower than that of carnauba wax / beeswax oleogels.Polarizing light microscope analysis showed that the crystal morphology of carnauba wax /rice bran wax-Tween oleogels was mainly needle-like or rod-like structure,accompanied by needle-like / rod-like to form compact large crystal aggregates.With the decrease of the ratio of carnauba wax or rice bran wax,the crystal morphology of the oleogels did not change obviously,and it was still rod-like or needle-like structure,accompanied by needle-like / rod-like aggregation,but the size and tightness of the aggregates decreased.The crystal morphology of beeswax-Tween oleogels mainly showed small and scattered needle-like structure,and some needle-like structures gathered and crossed to form petal-like structure.with the decrease of beeswax ratio,the crystal morphology of beeswax-Tween oleogels did not change obviously.the crystal size and crystal distribution are affected by the type of Tween and the ratio of beeswax to Tween.Thirdly,the physical properties of Tween-wax composite oleogels were studied by analyzing the oil holding capacities and texture properties.For carnauba wax / rice bran wax-Tween oleogels,with the decrease of the ratio of carnauba wax or rice bran wax,the oil holding capacities of the oleogels was also reduced,but the oil holding capacity could reach 90% or more.For beeswax-Tween oleogels,the oil holding capacities of almost all the oleogels can reach 100%,which is related to the fine needle-like structure of beeswax.The analysis of texture properties showed that among the three kinds of wax-Tween oleogels system,beeswax-Tween oleogels has the strongest hardness value,which is related to the microstructure of its crystal.Carnauba wax-Tween oleogels has strong cohesion and recovery,while rice bran wax-Tween oleogels has the weakest adhesion.Finally,through the constant temperature storage experiments of beeswax-Tween oleogels,the oxidation stability of beeswax-Tween oleogels was studied.The results showed that the acid value,peroxide value and anisidine value of all oleogels increased with the storage time,but the increase was not obvious when stored at 20? for 90 days.During the storage period,with the decrease of beeswax ratio(the increase of Tween ratio),the peroxide value and anisidine value of oleogels decreased as a whole,indicating that within the range of study,the appropriate increase of Tween ratio could effectively delay the oxidative rancidity of the oleogels.