Effect of Oil Hydrophobicity on the Adsorption and Rheology of β‑Lactoglobulin at Oil–Water Interfaces

The
adsorption of protein layers at oil–water interfaces
is critical to the formation and stability of various emulsions in,
for example, technical applications as well as in biological lipid
storage. Effects of ionic strength, pH, temperature, and pretreatments
of the proteins are well-known. However, the oil phase has been regarded
as exchangeable and its role in protein adsorption has been widely
ignored. Herein, the influence of systematically selected oil interfaces
of high purity on the formation and properties of β-lactoglobulin
(β-lg) adsorption layers was evaluated. Droplet profile tensiometry
and interfacial rheometry were employed to determine the adsorption
kinetics and dilatational and interfacial shear moduli. We show that
depending on the molecular size, flexibility, hydrophobicity, polarity,
and polarizability of the oils, globular proteins adsorb distinctively.
Stronger interactions of polar oils with the hydrophilic exterior
of the native β-lg lead to decelerated protein unfolding. This
results in lower surface pressures and slower formation of viscoelastic
networks. In addition, polar oils interact stronger with the protein
network by hydrophilic bonding and thereby act as softening agents.
The observed effects of hydrophobic subphases on the adsorbed protein
layers provide knowledge, which promotes higher reproducibility in
rheological studies and precise tailoring of interfacial films for
enhanced formation and stability of emulsions.

蛋白质层在油-水界面的吸附行为，对于各类乳液的形成与稳定性至关重要，这一现象广泛存在于工业应用与生物脂质储存体系中。离子强度、pH值、温度以及蛋白质预处理方式对吸附过程的影响已被广泛研究。但长期以来，油相被认为是可替换的组分，其在蛋白质吸附中的作用被极大忽视。本研究针对系统筛选得到的高纯度油相界面，探究其对β-乳球蛋白（β-lactoglobulin, β-lg）吸附层的形成过程与界面性质的影响。研究采用液滴轮廓张力法与界面流变学方法，测定了吸附动力学、扩张模量以及界面剪切模量。结果表明，球状蛋白质的吸附行为会因油相的分子尺寸、柔性、疏水性、极性与极化率差异而呈现显著区别。极性油相与天然β-乳球蛋白亲水表面的相互作用更强，会延缓蛋白质的解折叠过程，进而导致更低的界面压与黏弹性网络的形成速率放缓。此外，极性油相可通过亲水键与蛋白质网络形成更强相互作用，从而发挥软化剂的作用。本研究揭示的疏水亚相对吸附蛋白质层的影响机制，可为流变学研究提升重复性提供理论支撑，同时也可为精准调控界面膜以强化乳液的形成与稳定性提供指导。