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

BSTRACT 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. [ABSTRACT FROM AUTHOR]