Abstract: The Maillard reaction has been reported to be capable of improving the functional properties of soybean protein isolate (SPI). In this work, the effects of temperature, reaction time and mixing ratio on the Maillard reaction between SPI and glucose/maltose were studied, and the changes in solubility, emulsifying activity, solution pH, ζ potential, structure and molecular mass of Maillard reaction products were measured. The results indicated that the optimum reaction conditions were determined as mass ratio between SPI and sugar 4:1, temperature 80 ℃ and duration 6 h. The reaction markedly improved the solubility of SPI and maltose was more effective than glucose in improving this parameter. The reaction reduced the emulsifying activity and affected the ζ potential of SPI. As the Maillard reaction proceeded, the negative charge carried by SPI decreased obviously. The Maillard reaction reduced the pH of SPI solution. Thermal analysis revealed that the modification decreased the thermal stability of SPI. Fourier transform infrared spectroscopy confirmed the introduction of new groups into SPI. Moreover, the Maillard reaction enhanced the fluorescence intensity of SPI. Sodium dodecyl sulfate polyacrylamide gel electropheresis (SDS-PAGE) showed the formation of large molecules.

Key words: soybean protein isolate, glucose, maltose, wet heating method, Maillard reaction