Interfacial rheology of alkali pH-shifted myofibrillar protein at O/W interface and impact of Tween 20 displacement

In the current study, the interfacial rheological properties of alkali pH-shifted MP under pH 11.0 → 7.0, pH 11.5 → 7.0 and pH 12.0 → 7.0 have been firstly investigated. The molecular weight and microstructure of myofibrillar protein (MP) treated by alkali pH-shifting were investigated by gel-permeation chromatography (GPC) and transmission electron microscopy (TEM). Results indicated a swollen, organized and aggregated structure of refolded MP. Overall, the molecular change in refolded MP led to faster protein adsorption towards the O/W interface, enhanced intermolecular interaction between adsorbed proteins and improved elasticity of interfacial film compared to native MP. After β-mercaptoethanol (β-ME) was added, the advantage of refolded MP in diffusion phase no more existed due to the disruption of aggregation and decreased molecular size, besides the penetration and rearrangement were interfered because the disruption of disulfide bond inhibited the formation of interfacial protein layers. With the protein concentration increasing, MP molecules crowding at O/W (oil in water) surface limited the development of a highly elastic network. As revealed by Tween 20 displacement, MP layers with higher interfacial elasticity were more resistant to displacement. Moreover, after displacement the coalescence stability of emulsion droplet was enhanced but the mechanical strength of interfacial MP layer was reduced. Altogether MP (0.04 or 0.2 mg/mL) treated by pH 11.0 → 7.0 exhibited the best adsorption performance and interfacial properties, which were important in stablizing emulsions. Thus, interfacial behavior regulation by alkali pH-shifting may be a applicable process for developing meat protein-based emulsions in food industry.