Department of Food Science, University of Guelph, Guelph, ON N1G 2W1, Canada.
Faculty of Biotechnology and Food Engineering, Technion-Israel Institute of Technology, 32000 Haifa, Israel.
Food Res Int. 2017 Jan;91:1-10. doi: 10.1016/j.foodres.2016.11.024. Epub 2016 Nov 19.
In the present study we have characterized the influence of the polymer gelator ethylcellulose (EC) on the crystallization behavior of mixtures of stearyl alcohol and stearic acid (SOSA). The presence of EC led to a more abrupt thermo-reversible crystallization process and an increase in the onset of crystallization temperature from 22.7±0.35°C to 26.5±0.42°C. X-ray analysis indicated that the polymorphism of the mixed SOSA crystals was maintained in the presence of EC; however, changes in the small angle region indicated the presence of the polymer network altered the higher-order organization of the crystal network. Significant changes in the microstructural organization were also observed by light microscopy. A random distribution of needle-like, oriented platelets were observed in SOSA gels, while branched, feather-like structures were apparent in the mixed EC/SOSA system. Temperature-sweep rheological experiments of the combined EC/SOSA system also indicated that prior to crystallizing, SOSA molecules plasticized the polymer chains, resulting in a decrease in the gelation point (cross-over point; G'=G″) from ~110°C to 90°C. This effect was corroborated by DSC experiments, in which it was observed that the glass transition temperature of EC decreased and broadened with increasing SOSA content. Back extrusion flow curves indicated that the addition of EC reduces the brittleness and increases the plasticity of the bulk material, as indicated by the brittleness factor quantified over the steady-state flow regime, even when the combined gelator system was substantially firmer. Although the presence of the EC network resulted in a stress overshoot during initial penetration, by incorporating EC below its critical gelation concentration eliminated the overshoot while still providing plasticity to the SOSA network, such that the flow behavior was shown to be comparable to several commercial margarines. This study has demonstrated the ability of EC to modify the crystallization behavior of a low molecular weight oleogelator, while increasing the plasticity of the polymer network, to form a synergistic oleogelator system.
在本研究中，我们研究了聚合物凝胶剂乙基纤维素（EC）对硬脂醇和硬脂酸（SOSA）混合物结晶行为的影响。EC 的存在导致更突然的热可逆结晶过程，结晶起始温度从 22.7±0.35°C 增加到 26.5±0.42°C。X 射线分析表明，在 EC 存在下，混合 SOSA 晶体的多晶型性得以保持；然而，小角区域的变化表明聚合物网络的存在改变了晶体网络的高级组织。通过光学显微镜也观察到微观结构组织的显著变化。在 SOSA 凝胶中观察到针状、定向薄片的随机分布，而在混合 EC/SOSA 系统中则观察到分支、羽毛状结构。对 EC/SOSA 组合系统的温度扫描流变学实验也表明，在结晶之前，SOSA 分子使聚合物链增塑，导致凝胶点（交叉点；G'=G″）从~110°C 降低到 90°C。这一效应得到了 DSC 实验的证实，实验中观察到 EC 的玻璃化转变温度随着 SOSA 含量的增加而降低和变宽。背挤流动曲线表明，随着 EC 的加入，脆性因子在稳态流动区量化，即使在组合凝胶剂系统显著变硬的情况下，块状材料的脆性降低，塑性增加。尽管 EC 网络的存在导致初始穿透时出现应力过冲，但通过将 EC 加入到其临界凝胶浓度以下，消除了过冲，同时仍为 SOSA 网络提供了塑性，从而使流动行为与几种商业人造黄油相当。本研究表明，EC 能够改变低分子量油凝胶剂的结晶行为，同时增加聚合物网络的塑性，形成协同油凝胶剂系统。
