Rheological properties of whey protein and dextran conjugates at different reaction times

Protein/polysaccharide conjugates have been widely studied because of their good emulsifying properties and their potential use as food ingredients. However, there is little information about the use of these conjugates in gel systems. Rheological properties of conjugates of whey protein isolate (WPI) and dextran (DX) of 15 kDa obtained by Maillard reaction (RM) at different incubation times (2, 5 and 9 days) were studied. Conjugation was confirmed by electrophoresis, conformational changes were studied by DSC and rheological properties were determined by means of an oscillatory rheometer with a temperature ramp ranging from 25 to 90 °C. After each rheological measure, a mechanical spectrum from 0.01 to 10 Hz was also obtained. Electrophoresis indicated the presence of WPI/DX conjugates for all incubation days, though their molecular weight could not be determined. Both, time and temperature of gelation (G′–G″ crossover), increased in WPI/DX conjugate systems compared with WPI without DX (same time of incubation). However, these parameters decreased in WPI/DX mixed system. G′ values at 25 °C decreased in WPI/DX conjugates and increased in WPI/DX mixed system with respect to WPI alone. Frequency sweeps showed that all gels were stable.