Laneuville Sandra I, Turgeon Sylvie L, Sanchez Christian, Paquin Paul
Dairy Research Center STELA and Institute of Nutraceuticals and Functional Foods, Faculty of Agriculture and Food Science, Université Laval, Pavillon Paul-Comtois, Québec, Canada G1K-7P4.
Langmuir. 2006 Aug 15;22(17):7351-7. doi: 10.1021/la060149+.
The mechanism and kinetics of the electrostatic gelation of native beta-lactoglobulin-xanthan gum mixtures in aqueous solution is reported. The total biopolymer concentration at which gelation was obtained was extremely low (0.1 wt %) compared to the usually tested concentrations for protein-polysaccharide mixed gels (4-12 wt %). This is, to our knowledge, the first time that oppositely charged proteins and polysaccharides are reported to form a gel without applying any treatment to denature the protein (e.g. heating, enzymatic hydrolysis) and at such low concentrations. Static light-scattering and viscoelastic measurements allowed determination of the gelation kinetics. It was found that the gelation process initiated following a similar path as that of an associative phase separation process, i.e., with the formation of primary and interpolymeric electrostatic complexes. However, interpolymeric complexes were able to form clusters and junction zones that resulted in the freeze-in of the whole structure at the point of gelation. The formed gel is therefore a coupled-gel, that is, a gel that has junction zones involving two different molecules. The structuration of xanthan gum, even at these low concentrations, may have played a role in the structuration process. Due to the electrostatic nature of the gels, there was an optimum pH and macromolecular ratio at which the stability of the gels was maximal. This was related to the existence of a stoichiometric electrical charge equivalence pH, where molecules carry equal but opposite charges and protein-polysaccharide interactions are at their maximum.
报道了天然β-乳球蛋白-黄原胶混合物在水溶液中的静电凝胶化机制和动力学。与通常测试的蛋白质-多糖混合凝胶浓度（4-12 wt%）相比，形成凝胶时的总生物聚合物浓度极低（0.1 wt%）。据我们所知，这是首次报道带相反电荷的蛋白质和多糖在不进行任何使蛋白质变性的处理（如加热、酶水解）且在如此低浓度下形成凝胶。静态光散射和粘弹性测量能够确定凝胶化动力学。发现凝胶化过程起始路径与缔合相分离过程相似，即形成初级和聚合物间静电复合物。然而，聚合物间复合物能够形成簇和连接区，导致在凝胶化点整个结构冻结。因此形成的凝胶是一种耦合凝胶，即具有涉及两种不同分子的连接区的凝胶。即使在这些低浓度下，黄原胶的结构化可能在结构化过程中发挥了作用。由于凝胶的静电性质，存在一个最佳pH值和大分子比例，此时凝胶的稳定性最大。这与化学计量电荷等效pH值的存在有关，在该pH值下分子携带相等但相反的电荷，蛋白质-多糖相互作用达到最大值。
