Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, United Kingdom.
Langmuir. 2010 Oct 19;26(20):15901-8. doi: 10.1021/la102294u.
Understanding the effects of digestion conditions on the structure of interfacial protein networks is important in order to rationally design food emulsions which can moderate lipid digestion. This study compares the effect of gastric conditions (pH, temperature, and ionic strength) on β-lactoglobulin films at different fluid interfaces: air-water, tetradecane-water, and olive oil-water. The experiments have been designed to simulate the passage into the stomach media. Hence, preformed interfacial protein (β-lactoglobulin) networks have been exposed to gastric conditions in order to establish generic aspects of the digestion process. The results show that the presence of an oil phase affects both the unfolding of the protein at the interface on adsorption and the subsequent interprotein associations responsible for network formation at the interface. Furthermore, the effects of the physiological conditions characteristic of the stomach also altered differently the preformed protein layer at different fluid interfaces. Initially, the effects of temperature, acid pH, and ionic strength on the dilatational modulus of β-lactoglobulin adsorbed layers at tetradecane-water and olive oil-water interfaces were studied in isolation. The presence of salt was found to have a major effect on the dilatational response at the oil-water interface in contrast to the observations at the air-water interface: it enhanced intermolecular association, hence increasing the packing at the interface causing it to become more elastic. Exposure to acid pH (2.5) also increased the elasticity of the interface, possibly due to the fact that strong electrostatic interactions acting at the interface compensated for the reduced level of intermolecular association. However, the increase in dilatational modulus at the oil-water interface was less noticeable upon exposure to combined changes in acid pH and ionic strength, as would occur in the stomach. This is consistent with previously reported observations at the air-water interface. The quantitative differences in the response of the protein networks to gastric media at different fluid interfaces are discussed in terms of the conformation of β-lactoglobulin within the networks formed at each interface based on detailed theoretical modeling of adsorption data.
了解消化条件对界面蛋白网络结构的影响对于合理设计能够调节脂质消化的食品乳液非常重要。本研究比较了不同流体界面（气-水、十四烷-水和橄榄油-水）上胃条件（pH、温度和离子强度）对β-乳球蛋白膜的影响。实验设计模拟了进入胃介质的过程。因此，预先形成的界面蛋白（β-乳球蛋白）网络已经暴露在胃条件下，以确定消化过程的一般方面。结果表明，油相的存在既影响蛋白质在吸附时界面上的展开，也影响随后形成界面网络的蛋白质间相互作用。此外，胃中生理条件的影响也不同地改变了不同流体界面上预先形成的蛋白质层。最初，分别研究了温度、酸性 pH 和离子强度对十四烷-水和橄榄油-水界面上β-乳球蛋白吸附层的扩张模量的影响。结果发现，盐的存在对油-水界面上的扩张响应有重大影响，与在气-水界面上的观察结果相反：它增强了分子间的相互作用，从而增加了界面上的堆积，使其更具弹性。暴露于酸性 pH（2.5）也增加了界面的弹性，这可能是由于界面上的强静电相互作用补偿了分子间相互作用的减少水平。然而，在酸性 pH 和离子强度同时发生变化的情况下，油-水界面上的扩张模量增加不太明显，这与胃中可能发生的情况一致。这与在气-水界面上报告的先前观察结果一致。根据在每个界面上形成的蛋白质网络的构象，基于对吸附数据的详细理论建模，讨论了蛋白质网络对不同流体界面上胃介质的响应的定量差异。
