Chair of Food Chemistry, Technische Universität Dresden, 01062 Dresden, Germany.
J Agric Food Chem. 2020 Nov 25;68(47):13970-13981. doi: 10.1021/acs.jafc.0c04445. Epub 2020 Nov 4.
Casein gels consist of a fractal organized network of aggregated casein particles. The gel texture thereby depends on the structure, the spatial distribution, and the interaction forces of the network's elementary building blocks. The aim of this study was to explore the technofunctional consequences of a possible specificity of Maillard reaction-induced cross-linking reactions on casein with respect to texture and microstructure of acid gels. Therefore, sodium caseinate glycated with lactose in the dry state (60 °C, 0.5) was compared with casein samples cross-linked with methylglyoxal, with glutaraldehyde, or via microbial transglutaminase, respectively, at similar levels of protein cross-linking as confirmed by size-exclusion chromatography under denaturing conditions. Casein gels prepared by acidification with glucono-δ-lactone were characterized concerning pH kinetics during gelation, mechanical texture properties under large deformation, and water-holding capacity, while viscometric properties of casein suspensions were obtained prior to gelation. The gel microstructure was captured by confocal laser scanning microscopy and evaluated by means of image texture analysis. All protein cross-linking reactions studied led to an enhanced gel strength which was accompanied by an increased interconnectivity of the gel network and a decrease in apparent pore sizes. Gels with more densely packed strands, as was the case for enzymatically modified casein, exhibited pronounced mechanical stability. The spontaneous destabilization of the gel network upon prolonged glycation reactions, which was not obviously displayed by microstructural features but connected to an increased viscosity and pronounced pseudoplastic flow of the unacidified suspension, suggests a limitation of particle rearrangements and the weakening of interparticle protein-protein interactions by additional structure attributes formed during the early Maillard reaction (glycoconjugation).
酪蛋白凝胶由聚集的酪蛋白颗粒的分形组织网络组成。凝胶的质地取决于网络基本构建块的结构、空间分布和相互作用力。本研究的目的是探索美拉德反应诱导的交联反应对酪蛋白的技术功能后果，特别是对酸凝胶的质地和微观结构的影响。为此，将在干燥状态下（60°C，0.5）用乳糖糖化的乳清酸钠酪蛋白与分别用甲基乙二醛、戊二醛或通过微生物转谷氨酰胺酶交联的酪蛋白样品进行比较，根据变性条件下的排阻色谱证实，蛋白质交联水平相似。通过戊二酸-δ-内酯酸化制备的酪蛋白凝胶，在凝胶化过程中的 pH 动力学、大变形下的机械质地特性和持水能力方面进行了研究，同时在凝胶化之前还获得了酪蛋白悬浮液的粘度特性。通过共焦激光扫描显微镜捕获凝胶的微观结构，并通过图像纹理分析进行评估。研究中所有的蛋白质交联反应都导致凝胶强度增强，同时凝胶网络的连通性增加，表观孔径减小。具有更密集的链的凝胶，如酶改性酪蛋白，表现出明显的机械稳定性。在长时间的糖化反应中，凝胶网络的自发不稳定性，虽然没有明显表现在微观结构特征上，但与未酸化悬浮液的粘度增加和明显的假塑性流动有关，这表明颗粒重排受到限制，并且颗粒间的蛋白质-蛋白质相互作用由于早期美拉德反应（糖基化）形成的额外结构属性而减弱。
