Modification of the soy protein isolate surface at nanometric scale and its effect on physicochemical properties

The objective of this research was to modify at nanoscopic scale the surface of soy protein isolate (SPI) to improve its physicochemical properties. Nanostructured soy protein isolate (NSPI) was obtained by freezing SPI in liquid nitrogen and subsequent freeze drying. AFM images showed a rough surface for NSPI with valleys and cavities with diameters ranging from 8 to 15 nm. SPI presented a smooth surface and cavities with diameters in the order of 50-150 nm. According to the thermographic analysis, the homogeneous nanocavities formed on the surface by the nanostructuration process, allowed for an orderly arrangement of water molecules and hence a better heat distribution in the NSPI than in SPI. The spin-lattice relaxation times of adsorbed water molecules were lower in NSPI than in SPI at the whole water activity range. Gelling, water holding and oil absorption capacity were higher for NSPI than SPI, and both materials had similar emulsifying capacity.