Effect of milk protein products on the rheological and thermal (DSC) properties of normal rice starch and waxy rice starch

The effects of four milk protein ingredients, namely skim milk powder (SMP), milk protein concentrate (MPC), sodium caseinate (NaCN) and whey protein isolate (WPI), on the pasting behaviour of a 10% normal rice starch or waxy rice starch solution were assessed using rheological and differential scanning calorimetry (DSC) measurements and confocal scanning laser microscopy (CSLM). It was found that all these milk protein ingredients affected markedly and differently the pasting behaviour of the two rice starches. For instance, for normal rice starch, SMP and NaCN shifted the temperature of peak viscosity to higher temperatures, whereas MPC and WPI reduced the temperature of peak viscosity. For waxy rice starch, SMP, NaCN and WPI increased the temperature of peak viscosity, but MPC did not affect it. The value of the peak viscosity was also either increased or decreased, depending on the milk protein type and its concentration. The onset temperature measured by DSC correlated very well with that measured by rheology. However, there was no correlation between the peak temperature measured by DSC and that measured by rheology. This could have been due to, for example, phase separation between the milk proteins and the starch molecules, as clearly observed by CSLM for SMP/rice starch and MPC/rice starch mixtures.