Glycation of soy protein isolate with maltodextrin through Maillard reaction via dry and wet treatments and compare their techno-functional properties

Protein–polysaccharide Maillard conjugate has recently got much attention for improving protein functionality. In this study, soy protein isolate (SPI) was conjugated to maltodextrin (MD) at the protein-to-polysaccharide ratio of 1:2, 1:1 and 2:1 (w/w) via Maillard reaction by dry heating (60 °C, 0–9 days) or wet heating (90 °C, 0–120 min). The influences on the degree of graft (DG), functionalities and structure of conjugates were evaluated. The mass ratio of reactants and reaction time greatly impacted the DG of conjugates. The conjugates with protein-to-polysaccharide ratio of 1:2 (w/w) prepared via dry- and wet-heating methods exhibited the highest DG. The DG of dry heat-induced conjugates raised significantly as incubation for 3 days and prolonged heating has no effect of DG, whereas the DG of wet-heat conjugates increased as extended heating period. The emulsifying properties were sharply improved in the conjugates by dry heating as prolonging the incubation time. Protein solubility and foaming properties of the conjugates by dry heating incubated for a day were enhanced. Extending the reaction period negatively impacted those functionalities. On the other hand, wet heating profoundly enhanced the protein solubility and foaming properties of the conjugates. The structural characteristics by Fourier transform infrared spectrum (FTIR) and circular dichroism (CD) confirmed the conformational changes in the secondary structure of the conjugates prepared by dry- and wet-heating methods. The appropriate Maillard reaction conditions could formulate the conjugate with better functionalities that will be useful for food applications.