Plant fructans stabilize phosphatidylcholine liposomes during freeze-drying

Fructans have been implicated as protective agents in the drought and freez ing tolerance of many plant species. A direct proof of their ability to sta bilize biological structures under stress conditions, however, is still lac king. Here we show that inulins (linear fructose polymers) isolated from ch icory roots and dahlia tubers stabilize egg phosphatidylcholine large unila mellar vesicles during freeze-drying, while another polysaccharide, hydroxy ethyl starch, was completely ineffective. Liposome stability was assessed a fter rehydration by measuring retention of the soluble fluorescent dye carb oxyfluorescein and bilayer fusion. Inulin was an especially effective stabi lizer in combination with glucose. Analysis by HPLC showed that the commerc ial inulin preparations used in our study contained no low molecular mass s ugars that could be responsible for the observed stabilizing effect of the fructans. Fourier transform infrared spectroscopy showed a reduction of the gel to liquid-crystalline phase transition temperature of dry egg PtdCho b y more than 20 degrees C in the presence of inulin. A direct interaction of inulin with the phospholipid in the dry state was also indicated by dramat ic differences in the phosphate asymmetric stretch region of the infrared s pectrum between samples with and without the polysaccharide.