不同单硬脂酸甘油酯含量的大豆油油凝胶性能和微观结构分析

Analysis of properties and micro-structure of soybean oil oleogels containing different 1-stearoyl-rac-glycerol contents

[目的]本文旨在研究不同含量单硬脂酸甘油酯与大豆油形成的油凝胶的性能。[方法]试验所用单硬脂酸甘油酯含量分别为3%、5%、7%、9%、12%和15%(质量分数),通过测定油凝胶的临界成胶含量、硬度、持油性、流变性、热性能、化学键的相互作用以及双折射现象对油凝胶的三维网络结构和凝胶机制进行研究。[结果]单硬脂酸甘油酯在大豆油中的临界成胶含量为7%。随着单硬脂酸甘油酯含量增加,油凝胶的硬度和持油性提高,单硬脂酸甘油酯含量为15%时的凝胶强度和持油性分别高达(1.03±0.09)N和99.84%;表观黏度、复合模量增大,仍为触变性流体;凝胶强度和配位数增大。热分析表明:凝胶因子有固态的亚阿尔法相与反向层状相、反向层状相与液态的各向同性相间的转变,由于过冷现象,融解峰总是在结晶峰的右侧;凝胶因子的含量对油凝胶的相转变温度没有显著影响,由于大豆油的稀释效应,纯的单硬脂酸甘油酯的相转变温度要比油凝胶的高。傅里叶变换红外光谱分析表明:单硬脂酸甘油酯形成的分子间氢键是维持油凝胶三维网络结构的主要作用力。偏振光显微镜分析表明凝胶因子含量越高,三维网络结构越致密、双折射现象越明显。[结论]改变单硬脂酸甘油酯的含量可以调整油凝胶的性能和微观结构。

[Objectives]Properties of oleogels containing different 1-stearoyl-rac-glycerol contents were investigated.[Methods]The 1-stearoyl-rac-glycerol contents investigated included 3%,5%,7%,9%,12%and 15%(m/m).The three dimension network structure and gelling mechanism of oleogels were investigated by critical gelling content,hardness,oil binding capacity,rheological property,thermal property,and interaction of chemical bonds as well as birefringence phenomenon.[Results]Flowing property of oleogels in the glass test tubes was determined.The critical gelling content of 1-stearoyl-rac-glycerol in soybean oil was 7%.Both hardness and oil binding capacity of oleogels were improved with increasing contents of 1-stearoyl-rac-glycerol,and oleogels containing 15%of 1-stearoyl-rac-glycerol made hardness of(1.03±0.09)N as well as oil binding capacity of 99.84%.Flow curve tests with three-shear rate sweeps indicated that oleogels containing 1-stearoyl-rac-glycerol belonged to thixotropic fluid.The increase of contents of 1-stearoyl-rac-glycerol didn’t change the fluid type,but it increased oleogels’apparent viscosity.In the first stage of shear rate sweeps,there existed structure breakage of a more structured crystalline network with the increase of shear rate due to the existence of obvious stress overshoot.The hysteresis curves mainly belonged to the second and third stages of shear rate sweeps.Strain sweep tests from 0.01%to 100%at a fixed frequency of 1 Hz indicated that oleogels were in linear viscoelastic range at the strain of 0.02%,and complex modulus was improved with increasing contents of 1-stearoyl-rac-glycerol.In frequency sweep tests from 1 to 100 Hz oleogels’strength and coordination number at a controlled strain of 0.02%were obtained.With the increase of 1-stearoyl-rac-glycerol contents,oleogels exhibited greater gel strength.What’s more,the increase of coordination number indicated that denser three-dimension network structure was formed by stacking of molecular crystals.In cooling and heating process obtained by differential scanning calorimeter(DSC),pure 1-stearoyl-rac-glycerol showed two phase transition peaks respectively.Lower temperature peaks were the transitions between solid sub-alpha and inverse lamellar phase,and higher temperature peaks were the transitions between inverse lamellar phase and liquid isotropic phase.Supercooling phenomenon resulted in the temperature difference between crystallizing peaks and melting peaks,and the melting peaks were always on the right side of crystallizing peaks.Contents of 1-stearoyl-rac-glycerol had no significant influence on phase transition temperature of oleogels.Compared with oleogels,pure 1-stearoyl-rac-glycerol had higher phase transition temperature,which was due to diluting effect of soybean oil.Fourier transform infrared spectrum(FTIR)made clear that hydrogen bonds among 1-stearoyl-rac-glycerol molecules were conductive to the formation of three-dimension network structure independent of 1-stearoyl-rac-glycerol contents.With the increase of 1-stearoyl-rac-glycerol contents,birefringence phenomenon of crystals in oleogels became more obvious by polarization microscope,and denser three-dimension network structure was obtained.[Conclusions]The properties and micro-structure of oleogels were changed by 1-stearoyl-rac-glycerol contents.