Impact of pH on the interaction between soybean protein isolate and oxidized bacterial cellulose at oil-water interface: Dilatational rheological and emulsifying properties

The utilizations of the complexes or coacervates of protein/polysaccharide generated by electrostatic interactions to stabilize Pickering emulsions have attracted increasing attentions. In this work, the effect of pH on the conformational states, interfacial adsorption characteristics and emulsifying properties of soybean protein isolate/oxidized bacterial cellulose (SPI/TOBC) complexes had been investigated. The spectroscopy analysis, including far-UV circular dichroism and intrinsic tryptophan fluorescence spectroscopy, was applied to evaluate protein conformational transitions. The interfacial adsorption behaviors were characterized by using adsorption kinetics and dilatational viscoelasticity modulus analysis. According to spectroscopy analysis, the addition of TOBC reduced surface hydrophobicity of SPI at pH 2-9, since the added TOBC partially hinder SPI unfolding to decrease the formation of unordered structure. Moreover, the interfacial adsorption property of SPI around isoelectric point (pl, pH 4.5) was improved in the presence of TOBC with increased balanced interfacial surface pressure (pi) and diffusion rate constant (K-diff) values, while the viscoelastic modulus had no significant difference, and the emulsions stabilized with SPI/TOBC complexes exhibited uniform droplets distributions and smaller sizes (<20 mu m) at pH 4-5. This work would provide some guidance for the emulsions stabilized by using protein/polysaccharide complexes and has a practical application in food industry.