Controlled release of alpha-lipoic acid through incorporation into natural polysaccharide-based gel beads

Alpha-lipoic acid (ALA) is an essential cofactor for mitochondrial multi-enzyme complexes related to energy production. However, it is unstable under light and heat and its biological half-life (t1/2) is short. In this study, ALA was incorporated into alginic acid (Alg) gel beads to achieve stabilisation and sustained release. The cationic polymer chitosan (CS) was also added to the Alg gel beads to better control ALA release. In artificial gastric juice (pH 1.2), ALA release from the Alg gel beads was controlled through simple diffusion from the gel matrix. However, in artificial intestinal juice (pH 6.8), the Alg gel beads were immediately disintegrated. On the other hand, Alg gel beads with CS were not disintegrated in artificial intestinal juice (pH 6.8), and achieved pH-independent sustained release of ALA through an electrostatic interaction between the carboxyl groups of Alg and the amino groups of CS. ALA contained within the Alg gel beads was protected from light (UV) and heat (65 °C) compared with ALA alone. Addition of CS to the Alg gel beads further increased the stability of ALA. Thus, stabilisation and controlled release of ALA was achieved through incorporation of ALA in Alg gel beads containing CS.