Structure and property changes of the maltose-glycated caseinate prepared through the Maillard reaction in an ionic liquid medium

Protein glycation via the Maillard reaction is widely used to modify the functional properties of proteins. Using four explored reaction conditions, two maltose-glycated caseinate products GCN-I and GCN-II with maltose contents of 30.86 and 8.76 g/kg protein were prepared by this reaction in an ionic liquid and water as reaction media, respectively. The ionic liquid promoted caseinate glycation via decreasing water content and shifting reaction equilibrium, and thereby resulted in greater changes in property. Compared with unreacted caseinate and GCN-II, GCN-I had more −OH groups in its molecules, ordered secondary structure, larger hydrodynamic radius (181.3 versus 130.7 and 155.6 nm) and negative zeta-potential (−27.3 versus −19.1 and −22.9 mV) in aqueous dispersion, improved emulsifying properties, but decreased surface hydrophobicity and in vitro digestibility. GCN-I also showed reduced thermal stability during a heating process of 20-400 °C with the lowest decomposition temperature (291.4 °C versus 297.6 °C and 293.4 °C), largest total mass loss (62.7% versus 49.9% and 54.5%), and smallest enthalpy change (2.0 versus 4.9 and 3.3 kJ/g). Thus, ionic liquids might be interesting and promising non-aqueous solvents for protein glycation to promote glycation extent and property changes efficiently.