Institute of Pharmaceutical Science, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, United Kingdom.
Biomacromolecules. 2011 Oct 10;12(10):3741-52. doi: 10.1021/bm2009894. Epub 2011 Aug 26.
This Article investigates different types of networks formed from tilapia fish gelatin (10% w/w) in the presence and absence of the enzymatic cross-linker microbial transglutaminase. The influence of the temperature protocol and cross-linker concentration (0-55 U mTGase/g gelatin) was examined in physical, chemical, and hybrid gels, where physical gels arise from the formation of triple helices that act as junction points when the gels are cooled below the gelation point. A combination of rheology and optical rotation was used to study the evolution of the storage modulus (G') over time and the number of triple helices formed for each type of gel. We attempted to separate the final storage modulus of the gels into its chemical and physical contributions to examine the existence or otherwise of synergism between the two types of networks. Our experiments show that the gel characteristics vary widely with the thermal protocol. The final storage modulus in chemical gels increased with enzyme concentration, possibly due to the preferential formation of closed loops at low cross-linker amount. In chemical-physical gels, where the physical network (helices) was formed consecutively to the covalent one, we found that below a critical enzyme concentration the more extensive the chemical network is (as measured by G'), the weaker the final gel is. The storage modulus attributed to the physical network decreased exponentially as a function of G' from the chemical network, but both networks were found to be purely additive. Helices were not thermally stabilized. The simultaneous formation of physical and chemical networks (physical-co-chemical) resulted in G' values higher than the individual networks formed under the same conditions. Two regimes were distinguished: at low enzyme concentration (10-20 U mTGase/g gelatin), the networks were formed in series, but the storage modulus from the chemical network was higher in the presence of helices (compared to pure chemical gels); at higher enzyme concentration (30-40 U mTGase/g gelatin), strong synergistic effects were found as a large part of the covalent network became ineffective upon melting of the helices.
本文研究了在存在和不存在酶交联剂微生物转谷氨酰胺酶的情况下，由罗非鱼明胶（10%w/w）形成的不同类型的网络。考察了温度方案和交联剂浓度（0-55 U mTGase/g 明胶）对物理、化学和混合凝胶的影响，其中物理凝胶是由形成的三螺旋形成的，当凝胶冷却到凝胶点以下时，三螺旋作为连接点。流变学和旋光法的组合用于研究每种类型凝胶的储能模量（G'）随时间的演变和形成的三螺旋数量。我们试图将凝胶的最终储能模量分解为其化学和物理贡献，以检查两种网络之间是否存在协同作用。我们的实验表明，凝胶特性随热方案而有很大差异。化学凝胶的最终储能模量随酶浓度的增加而增加，这可能是由于在低交联剂含量下优先形成闭环。在化学-物理凝胶中，其中物理网络（螺旋）是在共价网络之后形成的，我们发现，在低于临界酶浓度下，化学网络越广泛（如通过 G'测量），最终凝胶越弱。归因于物理网络的储能模量随化学网络的 G'呈指数下降，但发现这两种网络都是纯加性的。螺旋没有热稳定化。物理和化学网络的同时形成（物理-化学）导致的 G'值高于在相同条件下形成的单个网络。区分了两个区域：在低酶浓度（10-20 U mTGase/g 明胶）下，网络是串联形成的，但在存在螺旋的情况下，化学网络的储能模量更高（与纯化学凝胶相比）；在较高的酶浓度（30-40 U mTGase/g 明胶）下，发现了强烈的协同效应，因为大部分共价网络在螺旋融化时变得无效。
