Relation between interstitial fluid stability and volatiles retention in freeze-dried model systems (sugar-salt solutions)

Abstract

The stability of interstitial fluids during the process of freeze-drying of model systems containing 27.7% glucose and 18.5% NaCl, on the retention of an organic volatile (acetaldehyde, 500 ppm) was studied. The compositions of interstitial fluids showing no crystallisation on freezing but devitrification on thawing were calculated from data obtained by differential-scanning-calorimetry. It was shown by rotative viscosity measurements in a temperature range between 200 K and 231 K that devitrification of the interstitial fluid is always accompanied by pronounced viscosity changes. From the results it appears that the critical viscosity zone for devitrification is situated between 10 5 and 10 7 cP. These values necessary to prevent collapse of 10 7 and 10 10 cP, as described in the literature. Our data also show that whenever devitrification occurs during the freeze-drying process, a pronounced loss of volatiles (from 75% to about 35%) was observed.