Water mobility in acidified milk drinks studied by low-field 1H NMR

Low-field nuclear magnetic resonance (LF-NMR) transverse relaxation (T2) was used to characterise acidified milk drinks (AMDs) with varying composition. Pectin was added to the AMDs at concentrations of 0.0%, 0.1%, 0.3% or 0.5% and the protein used was either skim milk powder (SMP) or SMP with added whey protein concentrate. Distributed exponential analysis of the T2 relaxation revealed that the AMDs contained a single water component and that the T2 relaxation times and distributions differed significantly with respect to pectin concentration and protein type. Temperature profiles (5–25–5 °C) showed that pectin concentrations of 0.3% or 0.5% prevented phase separations in the AMDs as a consequence of heating and cooling, whereas a new free water component emerged in the samples with pectin concentrations of 0.0% or 0.1% pectin. Overall, LF-NMR provides a powerful tool for elucidating industrially relevant texture problems such as whey separation.