Preparation And Interfacial Stabilization Mechanism Investigations Of The Emulsions Stabilized By Natural Silk Fibroin

In this paper, novel emulsions with strong interfacial stability and good biocompatibility were prepared with silk fibroin extracted from natural cocoon shells instead of traditional low weight molecular surfactants. Through the investigations of the preparation method, micro-morphology, rheological behaviors, stability of the emulsions and the viscoelastic property of the silk fibroin at the air/water and different oil/water interfaces, the relationships among the formulation design, microstructure, bulk rheological behaviors, interfacial rheological behaviors and stability of the emulsions stabilized by silk fibroin were discussed. In this case, the interfacial stabilization mechanism and the influence factors and change tendency of the emulsions stabilized by silk fibroin can be obtained, and the formation of the ordered structures of silk fibroin molecules and the control and analysis methods of interfacial stabilization mechanism and interfacial stability can be revealed, which can provide novel technique and idea for the design, preparation and investigations of the emulsions stabilized by silk fibroin and solid theoretical and experimental foundation for the applications of silk fibroin emulsions in the fields of food industry, cosmetics and drug delivery systems.Firstly, stable emulsions were successfully prepared with silk fibroin aqueous solution as water phase and dodecane, butyl butyrate and hexanol as oil phases respectively, in which the silk fibroin aqueous solution was prepared through degumming in alkali solution, dissolution by LiBr solution and dialysis against water, and the effects of silk fibroin concentration (?SF), oil volume fraction (?o) and oil polarity on the type, droplet size and distribution, rheological behaviors and stability of the resultant emulsions were also investigated. The emulsions stabilized by silk fibroin is O/W type, and the droplet size decreases with an increase in ?SF and oil polarity but with a decrease in ?o. The droplet surface charge is negative for all the silk fibroin emulsions and influenced much more significantly by ?SF than ?o. Due to the existence of gel-like colloidal networks formed by the dispersed oil droplets, the silk fibroin emulsions show predominantly elastic behaviors (G' > G" and low phase angle in the dynamic oscillatory measurements). However, these droplet networks are not very strong, and remarkable shear-thinning behaviors occurs during the steady shear flow of these silk fibroin stabilized emulsions. Moreover, before the breakage of the droplet associations, the droplets are deformed in some emulsions with low ?SF and polar oil, thus causing the appearance of stress overshoot. The modulus, viscosity and yield stress become greater with the increase of ?SF, ?o and oil polarity, which is very beneficial for strengthening the creaming stability of the silk fibroin stabilized emulsions.Secondly, the morphology of the interfacial layers of silk fibroin and the interfacial rheological behaviors of silk fibroin at both air/water and oil/water interfaces were investigated, and the relationships between interfacial rheological behaviors and the micro-morphology and stability of emulsions were discussed. Due to amphiphilicity, the silk fibroin forms stable films at both air/water and oil/water interfaces, and these films exhibit fibrous network structures and high interfacial elastic modulus increasing with the silk fibroin concentration. Silk fibroin interfacial gel generated at the oil/water interface is more stable, stronger and tougher than that at the air/water interface, possessing greater interfacial yield strain and higher recovery ability after the nonlinear fracture.Finally, further investigation expectation of silk fibroin emulsion was brought forward. The research achievements of interfacial rheology in the foam and emulsion fields not only promote better understanding of the interfacial rheological behaviors of protein films, but also provide important theoretical basis and direction for people to exploit and utilize the proteins and their complexes as surface active agents and colloid stabilizers and predict the stability of emulsions and foams.