Gebhardt Ronald, Darvishsefat Novin
Chair of Soft Matter Process Engineering (AVT.SMP), RWTH Aachen University, 52062 Aachen, Germany.
Gels. 2023 Jul 3;9(7):538. doi: 10.3390/gels9070538.
Micellar casein fibers of defined size and internal structure can be produced by the extrusion of cold-renneted casein micelles into a warm, calcium-rich coagulation bath. Calcium phosphate contacts within the casein matrix are important for fiber stability and production but become less important under acidic pH conditions. We demonstrate this with swelling experiments in media with pH < 2, which we adjust with citric acid of different molarities. In contrast to the simple swelling of dried casein fibers in water, a two-phase process takes place in citric acid similar to swelling in 1 N HCl. However, instead of a second deswelling step, we observe in citric acid that the fiber swells further. The observation is explained by a pH-dependent transition from a rennet casein gel to an acidified rennet gel. This can be simulated with a kinetic model that couples two second-order rate equations via a time-varying ratio. The final swelling values decrease with increasing proton concentration via a scaling relation, which is also confirmed by swelling in other acids (HCl or acetic acid) in this pH range. We attribute this to a decrease in the molecular weights of the aggregated casein structures within the strands of the gel network.
通过将冷凝乳酶处理的酪蛋白胶粒挤压到温暖、富含钙的凝固浴中，可以生产出具有特定尺寸和内部结构的胶束状酪蛋白纤维。酪蛋白基质内的磷酸钙接触对纤维稳定性和生产很重要，但在酸性pH条件下重要性降低。我们通过在pH < 2的介质中进行溶胀实验来证明这一点，介质用不同摩尔浓度的柠檬酸调节。与干燥的酪蛋白纤维在水中的简单溶胀不同，在柠檬酸中发生了一个两相过程，类似于在1 N HCl中的溶胀。然而，在柠檬酸中我们观察到的不是第二个消溶胀步骤，而是纤维进一步溶胀。这一观察结果可以通过从凝乳酶酪蛋白凝胶到酸化凝乳酶凝胶的pH依赖性转变来解释。这可以用一个动力学模型来模拟，该模型通过一个随时间变化的比率耦合两个二阶速率方程。最终的溶胀值通过一个标度关系随着质子浓度的增加而降低，这在该pH范围内的其他酸（HCl或乙酸）溶胀中也得到了证实。我们将此归因于凝胶网络链内聚集酪蛋白结构分子量的降低。
