Stabilization of α-lipoic acid by complex formation with chitosan.

α-Lipoic acid (ALA) is an essential cofactor in mitochondrial multi-enzyme complexes related to energy production. However, it is unstable under light or heat, and its decomposition is accompanied by an unpleasant odor. Therefore, its stabilization by complex formation with the cationic polymer chitosan (CS) was investigated. The ALA dissolved in demineralized water was efficiently adsorbed on the precipitated insoluble CS particles, and an ALA-CS complex was obtained. The amount of ALA adsorbed on CS was affected by the CS species and the quantity ratio of ALA to CS. The ALA from the ALA-CS complex was released immediately by changing the pH. When ALA was incubated at 65°C, it melted and polymerized. In addition, some decomposition of ALA was also observed in the physical mixture of ALA with CS. However, the ALA-CS complex did not decompose at all under the same conditions. Thus, the stabilization of ALA was achieved by complex formation with CS. CS is useful as a material for the stabilization of ALA, leading to its clinical use.