Preparation of milk protein isolate/κ-carrageenan conjugates by maillard reaction in wet-heating system and their application to stabilization of oil-in-water emulsions

In this study, milk protein isolate (MPI) was conjugated with κ-carrageenan (CG) via the Maillard reaction in a wet-heating system at 65 °C for 48 h. As the Maillard reaction progressed, the browning intensity increased. The structural changes and formation of MPI-CG conjugates were confirmed through various analyses that proved their effective preparation via the Maillard reaction under the wet-heating system. Furthermore, we also investigated the rheological properties, fat droplet size distributions, and physical stability of emulsions stabilized by the MPI-CG mixture (0 h) immediately after mixing without heat treatment and MPI-CG conjugates with different reaction times. All emulsions exhibited shear-thinning behavior with lower flow behavior index values than 1 (n = 0.41–0.63), and their apparent viscosity (η_a,10) and consistency index (K) decreased with increasing reaction time. The MPI-CG conjugates produced larger fat droplets than the MPI-CG mixture (0 h), and the fat droplet size of the emulsions stabilized by the MPI-CG conjugates increased with increasing reaction time. Even so, the stability of the emulsions stabilized by the MPI-CG conjugates was improved when compared to the emulsion stabilized by the MPI-CG mixture (0 h), and the MPI-CG conjugate after a 12 h reaction time produced the most stable oil-in-water emulsion.