Encapsulation and Stabilization of α-Lipoic Acid in Cyclodextrin Inclusion Complex Electrospun Nanofibers: Antioxidant and Fast-Dissolving α-Lipoic Acid/Cyclodextrin Nanofibrous Webs

In this study, electrospinning of nanofibers from alpha-lipoic acid/cyclodextrin inclusion complex systems was successfully performed without having any polymeric matrix. Alpha-lipoic acid (alpha-LA) is a natural antioxidant compound which is widely used as a food supplement. However, it has limited water solubility and poor thermal and oxidative stability. Nevertheless, it is possible to enhance its water solubility and thermal stability by inclusion complexation with cyclodextrins. Here, hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) and hydroxypropyl-gamma-cyclodextrin (HP-gamma-CyD) were chosen as host molecules for forming inclusion complexation with alpha-LA. Accordingly, alpha-LA was inclusion complexed with HP-beta-CyD and HP-gamma-CyD by using very high concentrated aqueous solutions of CyD (200%, w/v) having 1/1 and 2/1 molar ratio of alpha-LA/CyD. Except alpha-LA/HP-beta-CyD (1/1) solution, other alpha-LA/CyD solutions were turbid indicating the presence of some noncomplexed alpha-LA whereas alpha-LA/HP-beta-CyD (1/1) solution was very homogeneous signifying that alpha-LA was fully complexed with HP-beta-CyD. Even so, electrospinning was performed for all of the alpha-LA/HP-beta-CyD (1/1 and 2/1) and alpha-LA/HP-gamma-CyD (1/1 and 2/1) aqueous solutions, and defect-free bead-less and uniform nanofibers were successfully obtained for all of the alpha-LA/CyD solutions. However, the electrospinning process for alpha-LA/CyD (1/1) systems was much more efficient than the alpha-LA/CyD (2/1) systems, and we were able to produce self-standing and flexible nanofibrous webs from alpha-LA/CyD (1/1) systems. alpha-LA was efficiently preserved during the electrospinning process of alpha-LA/CyD (1/1) systems and the resulting electrospun alpha-LA/HP-fiCyD and alpha-LA/HP-gamma-CyD nanofibers were produced with the molar ratios of similar to 1/1 and , similar to 0.85/1 (alpha-LA/CyD), respectively. The better encapsulation efficiency of alpha-LA in alpha-LA/HP-beta-CyD nanofibers was due to higher solubility increase and higher binding strength between alpha-LA and HP-beta-CyD as revealed by the phase solubility test. alpha-LA was in the amorphous state in alpha-LA/CyD nanofibers and both alpha-LA/HP-beta-CyD and alpha-LA/HP-gamma-CyD nanofibers were dissolved very quickly in water and also when they wetted with artificial saliva. Additionally, the antioxidant activity of pure alpha-LA and alpha-LA/CyD nanofibers was comparatively evaluated using ABTS radical cation assay. alpha-LA/CyD nanofibers have shown significantly higher antioxidant performance compared to pure alpha-LA owing to improved water solubility by CyD inclusion complexation. The thermal stability enhancement of alpha-LA in alpha-LA/CyD nanofibers was achieved compared to pure alpha-LA under heat treatment (100 degrees C for 24 h). These promising results support that antioxidant alpha-LA/CyD nanofibers may have potential applications as orally fast-dissolving food supplements.