How adsorbed proteins at solid interfaces impact the droplet propagation through micro capillaries

Abstract

Proteins are used in food technology as biological emulsifiers which stabilize the liquid/liquid interface by lowering the interfacial tension due to their amphiphilic character. Due to the rising use of sensitive animal- and plant-based proteins in the food industry, homogenization methods with low-shear and low mechanical and thermal stresses like premix-membrane emulsification got more and more attention. However, one drawback remains: the proteins tend to adsorb to the membrane surfaces causing problems like fouling and pore-blocking. Recently, it was also found that the adsorbed proteins alter the wettability of the system which is suspected to affect the droplet breakup [Giefer et al., “Impact of wettability on interface deformation and droplet breakup in microcapillaries,” Phys. Fluids 35, 042110 (2023)], but the mechanism behind is still unknown. The study addresses the question of the extent to which proteins influence droplet propagation in micro-capillaries within membrane emulsification. Protein adsorption at liquid/liquid and liquid/solid interfaces is considered within molecular dynamic simulations and the effect on the interfacial tension is quantified. Considering the Young–Dupré equation [M. E. Schrader, “Young-dupre revisited,” Langmuir 11, 3585–3589 (1995)], interfacial energies are converted into contact angles, which are validated with experimental studies. For this purpose, idealized pore structures are considered under variation of the dynamic contact angle, for which the Kistler equation [S. Kistler, “Hydrodynamics of wetting,” Wettability (CRC Press, 1993), Vol. 6] is used. The results show that the protein adsorption to liquid/solid interfaces alters the wettability. Computational fluid dynamics reveal the dependence of the droplet propagation and interfacial instabilities in dependence on the wettability.