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

Abstract

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.

Synthesis, physicochemical properties, and health aspects of structured lipids: A review

“…Similar results were also observed in a previous work by Sakuno, Matsumoto, Kawai, Taihei, and Matsumura (), where they compared the adsorption behaviors and structural changes of β ‑lactoglobulin at the DAG–water interface and TAG–water interface, and found that a larger concentration of proteins was adsorbed to the TAG–water interface with a higher degree of structure unfolding. In a recent work using a model O/W emulsion, it has been reported that an increase in oil polarity delayed the adsorption and denaturation of proteins, thus leading to slower formation of interfacial film with decreased mechanical strength (Figure 3c; Bergfreund et al., ), which can largely explain the above‐mentioned results when DAG oils are used as the oil phase in contrast to TAGs.…”

“…(a) The impact of addition of different concentrations of MAG or DAG on the interfacial tension of stripped soybean oil (SSO) (Chen et al., ); (b) The interfacial tension versus time for the 1 wt% sodium caseinate solution in the presence of peanut oil (PO) or peanut oil‐based diacylglycerol (PO‐DAG) (Long et al., ); (c) Schematic illustration of the effect of oil polarity on adsorption of β ‐lactoglobulin and interfacial film structure at oil–water interface in a model system (Bergfreund et al., ); (d) Microscopy images of oil foams formed by air bubbles dispersed in sunflower oil stabilized by MAGs: (left) cryo‐scanning electron microscopy (SEM) image, (middle) CLSM image, and (right) polarized light image (Heymans et al., )…”

“…TAGs have been fully or partially substituted by DAGs to produced emulsions with enhanced nutrition (Diao et al, 2016;Long et al, 2015;Ng, Lai, Abas, Lim, & Tan, 2014). It has been demonstrated that variation in the oil phase significantly influences adsorption behavior of emulsifiers, viscoelastic properties of the formed interfacial film, and emulsion stability (Bergfreund, Bertsch, Kuster, & Fischer, 2018;Zare, Allison, & Mcgrath, 2016;Zhai et al, 2011). Long et al (2015) constructed O/W emulsions stabilized by sodium caseinate with either peanut oil (PO) or peanut oil-based DAG oil (PO-DAG, 95.95% purity) as the oil phase.…”

“…Long et al (2015) constructed O/W emulsions stabilized by sodium caseinate with either peanut oil (PO) or peanut oil-based DAG oil (PO-DAG, 95.95% purity) as the oil phase. They observed that PO-DAG/water interface had a lower interfacial tension and almost remained constant, whereas the PO-water interface had a significantly higher initial interfacial tension and then decreased with the evolution F I G U R E 3 (a) The impact of addition of different concentrations of MAG or DAG on the interfacial tension of stripped soybean oil (SSO) (Chen et al, 2014); (b) The interfacial tension versus time for the 1 wt% sodium caseinate solution in the presence of peanut oil (PO) or peanut oil-based diacylglycerol (PO-DAG) (Long et al, 2015); (c) Schematic illustration of the effect of oil polarity on adsorption of -lactoglobulin and interfacial film structure at oil-water interface in a model system (Bergfreund et al, 2018); (d) Microscopy images of oil foams formed by air bubbles dispersed in sunflower oil stabilized by MAGs: (left) cryo-scanning electron microscopy (SEM) image, (middle) CLSM image, and (right) polarized light image (Heymans et al, 2018) of time. When protein adsorption equilibrium was reached, the interfacial tension of PO-water interface was slightly lower than that of the PO-DAG-water interface (Figure 3b).…”

Creating gradients of amyloid fibrils from the liquid–liquid interface

“…Ethanol is chosen as a spreading agent as it is known to have no short-term effects on BLG amyloid fibrils. 1,22 Hexane is also known to have no significant effects on BLG proteins, 23 thus constituting an appropriate choice for the non-polar phase. Using a Hamilton 10 ml microsyringe, the desired quantity of mixture is deposited directly at the interface and left to equilibrate for 10 minutes.…”