Modified mung bean protein: Optimization of microwave-assisted phosphorylation and its functional and structural characterizations

The optimization of microwave-assisted phosphorylation modification by sodium tripolyphosphate (STP) on mung bean protein (MBP) and its effect on functional and structural characterizations was studied. The results illustrated that the optimum phosphorylation conditions were: STP/protein ratio of 0.063 g/g, microwave power of 590 W, microwave time of 155 s, and pH of 7.8. As a result, the maximum phosphorylation degree of MBP, 3.27%, was reached at the optimized conditions. Also, structural characterization by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) revealed that the phosphate groups of STP were bound to the –NH2 and –OH groups of MBP with covalent interactions (C–O–P and C–N–P bounds). The enhanced functional properties of phosphorylated MBP may be due to the introduction of phosphate groups, which may form a large number of hydrogen bonds with water molecules, thus increasing the binding between proteins and water molecules. Furthermore, the introduction of phosphate groups increased the electronegativity of the protein system, improved the electrostatic repulsion between protein molecules, and made them disperse in the solution system more efficiently. This study proposed that microwave-assisted phosphorylation appeared to be a promising technique to expand its application in food systems.