The effect of storage temperature on interactions between dehydrated sugars and phosphatidylcholine

We studied the effects of storage temperature on the stability of dehydrated POPC (1-palmitoyl-2-oleoyl-phosphatidylcholine) mixed with sucrose, trehalose, or a sucrose/raffinose mixture. We used DSC to measure the gel-to-fluid phase transition temperature (T-m) of POPC after incubation either below or near the glass transition temperature (T-g) of the sugars in the mixture. Glass formation by the sugars around fluid-phase POPC led to the lowering of T-m below that of the fully hydrated lipid. Phospholipid phase behavior did not change during storage below T-g. In some samples stored above T-g, trehalose crystallized completely; in these samples, the T-m of POPC increased to that of the partially dehydrated phospholipid. Melting the crystalline sugar re-established its ability to lower POPC's T-m. We conclude that prevention of complete sugar crystallization was important for stability in the dry state, and that storage below T-g conferred long-term stability to the dehydrated sugar-lipid mixtures.