Effects of sucrose and trehalose on the preservation of the native structure of spray-dried lysozyme

Purpose. To investigate the effects of sucrose, trehalose, sucrose/ dextran mixtures, and sucrose/ trehalose mixtures on the preservation of the native structure of spray- dried lysozyme in the solid state. Methods. The intensity of the alpha-helical band and the melting enthalpies (DeltaH(m)) of spray-dried lysozyme in the dried form and in aqueous solution were obtained using second derivative FTIR and differential scanning calorimetry (DSC) respectively. Results. The intensity of the alpha- helical band and the DeltaH(m) of spray-dried lysozyme obtained were linearly correlated and both suggest that the stabilization of lysozyme in the dried form was excipient concentration- dependent with a close to maximum stabilization being conferred by sucrose or trehalose at a mass ratio 1- 2 (sugar: enzyme). Sucrose appeared to be more effective than trehalose on a weight by weight basis whilst stabilizing effects of dextran/ sucrose or trehalose/ sucrose mixtures were found to be additive. Conclusion. Dehydration during spray drying was considered the main stress to the denaturation of lysozyme. A major effect of the sugars in protecting lysozyme against dehydration was attributable to hydrogen bonding between the sugar and protein molecules, which lead to an increase in the change in the negative value of the free energy between native and denatured states.