Estimation of mass transfer rate and primary drying times during freeze-drying of frozen maltodextrin solutions based on x-ray μ-computed tomography measurements of pore size distributions

Petra Foerst*, Teresa Melo de Carvalho, Martin Lechner, Tijana Kovacevic, Seongshik Kim, Christoph Kirse, Heiko Briesen

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


The study presents a method to estimate the mass transfer rate during primary drying based on μ-computed tomographic measurements of a freeze-dried cake. The study was carried out in a defined setup in a lyomicroscope and confined geometry in which freezing occurred under homogeneous nucleation, and drying under mass-transfer-limited conditions. Pore size distribution, effective diffusivity, and primary drying rates of maltodextrin solutions at different weight concentrations (5%, 10%, and 20% (w/w))and different cooling rates were determined. Furthermore, the effect of annealing treatment on primary drying rate was studied. Two different annealing treatments were tested, one for 90 min at −10 °C and another for 180 min at −5 °C. It was shown that solid concentration and annealing above Tg’ have the strongest impact on pore size and, subsequently, on primary drying rate. Therefore annealing represents a powerful tool to accelerate primary drying which is the most time-consuming step during lyophilisation.
Original languageEnglish
JournalJournal of Food Engineering
Pages (from-to)50-57
Publication statusPublished - 2019


  • Drying kinetic
  • Freeze drying
  • Maltodextrins
  • X ray micro-computed tomography
  • Pore size
  • Knudsen diffusion

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