Interfacial adsorption and lubrication dynamics of β-lactoglobulin and MCT on the mucin layer

It is important to understand the interactions between salivary mucin and food-origin proteins or lipids, which play key roles in food oral lubrication and sensory perception. This study investigates the roles of β-lactoglobulin (BLG, at different pHs) and medium-chain triglycerides (MCT) on the adsorption and lubrication behavior of mucin in oral conditions. Lubrication tests suggested that BLG at pH 3.5 enhanced the friction coefficient of mucin more rapidly than at pH 6.8, particularly in the mixed and hydrodynamic regions, while MCT improved lubrication of the system at pH 6.8 but had no significant effect at pH 3.5. QCM-D tests revealed that BLG at pH 3.5 exhibited stronger binding, greater hydration, and faster adsorption onto mucin-coated surfaces compared to BLG at pH 6.8, forming a thicker, more viscoelastic adsorbed layer, which contributed to increased friction. MCT further influenced the structures of the adsorbed film, and the mucin-BLG3.5-MCT system formed a thicker and more stable layer than the mucin-BLG6.8-MCT system. Molecular docking suggested that BLG interacted with mucin via salt bridges, hydrophobic interactions, and hydrogen bonds at pH 3.5, and via hydrophobic interactions and hydrogen bonds at pH 6.8. MCT weakly bound to mucin via hydrophobic interactions, but interacted strongly with BLG, facilitating BLG removal from the mucin layer. These findings offer insights for designing biomimetic surfaces and functional materials with tailored tribological properties in diverse applications.