Characterization of bilayer emulsion of phosphorylated soybean protein isolate

In this paper, phosphorylating reagent sodium tripolyphosphate (STP) and sodium trimetaphosphate (STMP) were employed to revise soy protein isolate (SPI). Two phosphorylated soybean protein isolates (SPI-STP and SPI-STMP) were prepared by covalent reaction. Such results display that phosphorylation altered spatial structure of the SPI, with isoelectric point (pI) of SPI declined from 4.46 to 3.91 (SPI-STP) and 4.14 (SPI-STMP). Emulsification stability (ESI) and activity (EAI) and of the two phosphorylated SPI were significantly improved. Single-layer emulsions (SE, STPE and STMPE) were prepared from SPI, SPI-STP and SPI-STMP. On this basis, the single-layer emulsions were combined with chitosan (CS) to prepare the bilayer emulsion (SE-C, STPE-C and STMPE-C). As seen in the experiments, phosphorylated SPI bilayer emulsion was of smaller particle size than unphosphorylated SPI bilayer emulsions under electrostatic interaction. In contrast to SE-C and single-layer emulsions, the bilayer emulsion generated from phosphorylated SPI displayed the improved storage stability, and smallest variation in mean particle size of STPE-C. Meanwhile, STPE-C exhibited best resistance to negative influences of the variation in pH and temperature This work provides new materials for the delivery system of bioactive substances and demonstrates the broad application prospects of bilayer emulsions in traditional food processing fields.