Physical stability and microstructure of rapeseed protein isolate/gum Arabic stabilized emulsions at alkaline pH

Abstract The objective of this study was to investigate the effects of gum Arabic (GA) contents (0%–3%, w/v) and pH (7, 8 and 9) on the stability of 3% (w/v) rapeseed protein isolate (RPI) emulsion. The centrifugal precipitation rate, stability coefficient, interfacial adsorption protein content, droplet size and zeta potential, rheology, confocal laser scanning microscope (CLSM) and fourier transform infrared spectroscopy (FTIR) were measured. Results showed that the stability of emulsions varied with different GA contents and pH values. The most stability of RPI-stabilized emulsion was achieved when 1% of GA was added at pH 8. Under the optimal condition (1% GA being added at pH 8), the analysis of size and zeta potential of complexes revealed that the particle size was 314 nm, and largest absolute zeta potential value (−44.3 ± 0.5 mV) was obtained. CLSM microscopic observations further verified these results. In addition, the FTIR spectra showed the absorption peak of amide І and amide Ⅱ of RPI-GA complex decreased and were shifted compared to RPI alone, and the β-sheet was significantly increased whereas β-antiparallel was significantly decreased when 1% of GA was added at pH 8, indicating the interaction of RPI and GA mainly via the changing of hydrogen bonds.