Change in molecular structure and dynamics of protein in milk protein concentrate powder upon ageing by solid-state carbon NMR

Instability of proteins in dry form causes solubility loss of milk protein concentrate (MPC) powder upon ageing. High resolution solid state NMR techniques were used to investigate the changes in molecular structure and dynamics of proteins in MPC with varying moisture content (5.5–16.5% w/w) and storage period. The results indicate a slight higher rigidity of molecular domains of protein molecules of non-aged MPC compared to that of the long aged (at 25 °C) MPC. It could be suggested from this observation that long-term storage at high relative humidity (RH) may reduce rigidity of the molecular domains due to interaction with water rather than short-term storage at high RH. This may indicate increased molecular mobility of backbone and side chains of protein molecules due to plasticization during ageing which could facilitate protein–protein interaction and protein denaturation.