Effect of sucrose/raffinose mass ratios on the stability of co-lyophilizedprotein during storage above the T-g

Purpose. To examine the potential of raffinose as an excipient in stabilizi ng protein and to study the effect of sucrose/raffinose mass ratios on the stability of co-lyophilized protein and amorphous solids during storage at an elevated temperature. Methods. Glucose-6-phosphate dehydrogenase (G6PDH) was colyophilized with s ucrose and raffinose mixed at different mass ratios. The activity of dried G6PDH was monitored during storage at 44 degreesC. Thermal properties of su crose/raffinose matrices were determined by differential scanning calorimet ry (DSC). Results. Mass ratios of sucrose to raffinose did not affect the recovery of G6PDH activity after freeze-drying, but significantly affected the stabili ty of freeze-dried G6PDH during storage. The sucrose-alone formulation offe red the best enzyme stabilization during storage. With increasing fraction of raffinose, the G6PDH stability decreased, sugar crystallization inhibite d, and crystal-melting temperature increased. Conclusions, Despite the higher T, of the formulations with higher fraction of raffinose. they provided less protection for G6PDH than did sucrose alo ne during storage. Our data do not support the prediction from recent therm ophysical studies that raffinose should be superior to sucrose and trehalos e as a potential excipient or stabilizer.