The gastric digestion of proteins is influenced by the pH and the gastric pH fluctuates after food consumption. However, the dynamics of gastric pH still need to be quantitatively understood. Proteins in food strongly influences the gastric pH. Therefore, we studied the interaction between acid and proteins, including the buffer reaction and the acid diffusion in protein gels. The buffer capacity of proteins stems from its content of ionizable amino acid side groups. Based on this, we set up a model and method to parameterize the buffer capacity of proteins. Moreover, the liberated carboxyl and amino groups during enzymatic hydrolysis of protein can also contribute to the buffer capacity. While we expected protons to diffuse faster than pepsin, we found that the penetration distance of acid is comparable to that of pepsin. The buffer reaction caused the acid to concentrate tenfold in the gel compared to the bulk acid concentration. Therefore, we postulated that the buffer reaction reduces acid diffusivity in gels.

中文翻译：

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体外胃液条件 下酸与蛋白质之间的相互作用-理论和实验定量

胃内蛋白质的消化受pH值的影响，食物进食后胃pH值会发生波动。但是，胃pH值的动态变化仍需要定量了解。食物中的蛋白质会强烈影响胃的pH值。因此，我们研究了酸与蛋白质之间的相互作用，包括缓冲液反应和酸在蛋白质凝胶中的扩散。蛋白质的缓冲能力源于其可电离的氨基酸侧基的含量。基于此，我们建立了参数化蛋白质缓冲能力的模型和方法。此外，在蛋白质酶促水解过程中释放的羧基和氨基也可有助于缓冲能力。尽管我们预期质子的扩散速度要快于胃蛋白酶，但我们发现酸的渗透距离与胃蛋白酶相当。缓冲反应使酸在凝胶中的浓缩量是总酸浓度的十倍。因此，我们推测缓冲液反应会降低凝胶中的酸扩散性。