Monitoring Freeze-Drying by Low Resolution Pulse NMR: Determination of Sublimation Endpoint

ABSTRACT An NMR method was developed for detection of the sublimation period endpoint during the freeze‐drying of potato pieces. Longitudinal (T1 and transverse (T2) relaxation times were estimated using rapid NMR methods. Samples were immediately examined to determine presence of a frozen core. The plot of T1 vs T2 showed an abrupt increase at a point corresponding to the complete elimination of the frozen core. Similar Tj vs T2 curves were observed when monitoring freeze‐drying of a single potato piece inside the NMR probe‐head. The detection of an anomalous freeze‐drying is possible by monitoring the T1 the T2 or the free induction decay signal.