Efficient Stabilization and Directional-Controlled Release of Vitamin C in Disaccharide/Megasaccharide Composite Xerogels

Composite xerogel films with structural orientation, controlled swelling degree, and drug-release ability are prepared using biocompatible megamolecular liquid crystalline polysaccharide (sacran) secreted by a cyanobacterium Aphanothece sacrum. The sacran xerogel films (Sac-XFs) are formed by drying sacran aqueous solution including vitamin C (L-ascorbic acid, AA) and trehalose under various conditions. In X-ray diffraction and differential scanning calorimetry of Sac-XFs, diffractions or melting points of either AA or trehalose are not detected, indicating no crystal formation. Additionally, the stability of entrapped AA in Sac-XFs is evaluated through changes in film color and percentage loss, to indicate that AA stability is enhanced by entrapment in Sac-XFs in the presence of trehalose. Scanning electron microscopy of Sac-XFs reveals the morphological orientation, and number of striped lines along the longitudinal axis of film edges on side views while no visible textures in top views. When Sac-XFs are immersed in water, anisotropic swelling is observed, and anisotropy decreases with an increase in the drying temperature of the films. AA is released preferentially from the hydrogel sheet edges, indicating the direction-controlled release. Thus, the trehalose/sacran composite xerogels offer an alternative platform for preserving and controlled-releasing sensitive substances for fields of foods, pharmaceutics, and cosmetics.