Abstract
Adsorption of proteins to fluid interfaces is critical in many industries, scientific disciplines, and biological processes. However, the structural transitions of proteins upon adsorption and the effect of the hydrophobic subphase, such as oil, have received little attention. Herein, we present a comprehensive study on the effect of the hydrophobic subphase on the adsorption behavior of globular and random-coil proteins. The adsorption of proteins is limited by their structural stability, and accordingly, is faster for less stable globular proteins and fastest for random-coil proteins. Protein adsorption is slower at more polar oils, regardless of the protein type, structure, and stability. Moreover, we found a correlation of oil polarity and the induced surface pressure of proteins, which seems universally applicable and describes the experimental data of over 30 previous studies. The model works for all commonly applied subphases, with the exception of oils that chemically react with proteins (e.g. octanal) and air, due to the lack of hydrophobic interactions. These results foster our understanding of protein adsorption and allow the prediction of protein unfolding depending on protein-subphase interactions.
Highlights
Proteins are natural macromolecules with an amphiphilic structure, driving them to adsorb to fluid interfaces
The adsorption kinetics of surface-active compounds are commonly depicted by plotting the interfacial pressure
We have presented a systematic investigation of protein adsorption to fluid interfaces with different polarities
Summary
Proteins are natural macromolecules with an amphiphilic structure, driving them to adsorb to fluid interfaces. The interfacial tension [1,2,3,4] This property is used to stabilize foams and emulsions, essential in food, pharmaceutical, cosmetic, and agrochemical industries [1,5,6,7,74]. Besides the functional use of adsorbed proteins, the behavior of proteins at water-oil interfaces is subject of nutritional, medical and pharmaceutical research efforts in fields such as protein crystallization, lipid bodies, protein digestion, antibody stability, vaccination efficiency, biomimicking protocells, and cell membrane functions [8,9,10,11,12,13].
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