Surface pressure affects B-hordein network formation at the air–water interface in relation to gastric digestibility

• B-Hordein interfacial film formation under pressure and its degradation in simulated gastric fluid was studied.
• The digestion process of protein monolayer at the interface was visualized by AFM.
• B-Hordein could form a solid like coating at the interface.
• B-Hordein can tile the hydrophobic region from water to inhibit pepsin digestion.

Protein interfacial network formation under mechanical pressure and its influence on degradation was investigated at molecular level using Langmuir–Blodgett B-hordein monolayer as a 2D model. Surface properties, such as surface pressure, dilatational and shear rheology and the surface pressure − area (π − A) isotherm, of B-hordein at air–water interface were analyzed by tensiometer, rheometer and a Langmuir–Blodgett trough respectively. B-Hordein conformation and orientation under different surface pressures were determined by polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). The interfacial network morphology was observed by atomic force microscopy (AFM). B-Hordein could reduce the air–water surface tension rapidly to ∼45 mN/m and form a solid-like network with high rheological elasticity and compressibility at interface, which could be a result of interactions developed by intermolecular β-sheets. The results also revealed that B-hordein interfacial network switched from an expanded liquid phase to a solid-like film with increasing compression pressure. The orientation of B-hordein was parallel to the surface when in expended liquid phase, whereas upon compression, the hydrophobic repetitive region tilted away from water phase. When compressed to 30 mN/m, a strong elastic network was formed at the interface, and it was resistant to a harsh gastric-like environment of low pH and pepsin. This work generated fundamental knowledge, which suggested the potential to design B-hordein stabilized emulsions and encapsulations with controllable digestibility for small intestine targeted delivery of bioactive compounds.

Conformational changes of B-hordeins under compression at air/water interface and the responses of interfacial B-hordein networks to gastric digestion.Figure optionsDownload as PowerPoint slide