Department of Fiber Science & Apparel Design, College of Human Ecology , Cornell University , Ithaca , New York 14853 , United States.
J Agric Food Chem. 2019 Nov 27;67(47):13093-13107. doi: 10.1021/acs.jafc.9b05580. Epub 2019 Nov 14.
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 (α-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-β-CyD) and hydroxypropyl-gamma-cyclodextrin (HP-γ-CyD) were chosen as host molecules for forming inclusion complexation with α-LA. Accordingly, α-LA was inclusion complexed with HP-β-CyD and HP-γ-CyD by using very high concentrated aqueous solutions of CyD (200%, w/v) having 1/1 and 2/1 molar ratio of α-LA/CyD. Except α-LA/HP-β-CyD (1/1) solution, other α-LA/CyD solutions were turbid indicating the presence of some noncomplexed α-LA whereas α-LA/HP-β-CyD (1/1) solution was very homogeneous signifying that α-LA was fully complexed with HP-β-CyD. Even so, electrospinning was performed for all of the α-LA/HP-β-CyD (1/1 and 2/1) and α-LA/HP-γ-CyD (1/1 and 2/1) aqueous solutions, and defect-free bead-less and uniform nanofibers were successfully obtained for all of the α-LA/CyD solutions. However, the electrospinning process for α-LA/CyD (1/1) systems was much more efficient than the α-LA/CyD (2/1) systems, and we were able to produce self-standing and flexible nanofibrous webs from α-LA/CyD (1/1) systems. α-LA was efficiently preserved during the electrospinning process of α-LA/CyD (1/1) systems and the resulting electrospun α-LA/HP-β-CyD and α-LA/HP-γ-CyD nanofibers were produced with the molar ratios of ∼1/1 and ∼0.85/1 (α-LA/CyD), respectively. The better encapsulation efficiency of α-LA in α-LA/HP-β-CyD nanofibers was due to higher solubility increase and higher binding strength between α-LA and HP-β-CyD as revealed by the phase solubility test. α-LA was in the amorphous state in α-LA/CyD nanofibers and both α-LA/HP-β-CyD and α-LA/HP-γ-CyD nanofibers were dissolved very quickly in water and also when they wetted with artificial saliva. Additionally, the antioxidant activity of pure α-LA and α-LA/CyD nanofibers was comparatively evaluated using ABTS radical cation assay. α-LA/CyD nanofibers have shown significantly higher antioxidant performance compared to pure α-LA owing to improved water solubility by CyD inclusion complexation. The thermal stability enhancement of α-LA in α-LA/CyD nanofibers was achieved compared to pure α-LA under heat treatment (100 °C for 24 h). These promising results support that antioxidant α-LA/CyD nanofibers may have potential applications as orally fast-dissolving food supplements.
在这项研究中，成功地在没有任何聚合物基质的情况下，通过将 α-硫辛酸/环糊精包合物体系进行静电纺丝来制备纳米纤维。α-硫辛酸（α-LA）是一种天然抗氧化化合物，广泛用作食品补充剂。然而，它的水溶性有限，热稳定性和氧化稳定性差。尽管如此，通过与环糊精形成包合物可以提高其水溶性和热稳定性。在这里，羟丙基-β-环糊精（HP-β-CyD）和羟丙基-γ-环糊精（HP-γ-CyD）被选为与 α-LA 形成包合物的宿主分子。因此，通过使用 200%（w/v）的 CyD 高浓度水溶液（α-LA/CyD 的摩尔比为 1/1 和 2/1）将 α-LA 与 HP-β-CyD 和 HP-γ-CyD 包合。除了 α-LA/HP-β-CyD（1/1）溶液外，其他 α-LA/CyD 溶液均为混浊状，表明存在一些未复合的 α-LA，而 α-LA/HP-β-CyD（1/1）溶液非常均匀，表明 α-LA 已与 HP-β-CyD 完全复合。即便如此，仍对所有的 α-LA/HP-β-CyD（1/1 和 2/1）和 α-LA/HP-γ-CyD（1/1 和 2/1）水溶液进行了静电纺丝，成功地获得了无缺陷、无珠、均匀的纳米纤维。然而，α-LA/CyD（1/1）体系的静电纺丝过程比 α-LA/CyD（2/1）体系更有效，并且我们能够从 α-LA/CyD（1/1）体系中生产出自支撑和柔韧的纳米纤维网。α-LA 在 α-LA/CyD（1/1）体系的静电纺丝过程中得到有效保存，所得静电纺丝的 α-LA/HP-β-CyD 和 α-LA/HP-γ-CyD 纳米纤维的摩尔比分别约为 1/1 和约 0.85/1（α-LA/CyD）。α-LA/HP-β-CyD 纳米纤维中 α-LA 的包封效率更高，这是由于 α-LA 与 HP-β-CyD 之间的溶解度增加和结合强度更高，这一点通过相溶解度试验得到了揭示。α-LA 在 α-LA/CyD 纳米纤维中呈无定形状态，α-LA/HP-β-CyD 和 α-LA/HP-γ-CyD 纳米纤维在水中以及润湿人工唾液时都能迅速溶解。此外，使用 ABTS 自由基阳离子测定法比较评估了纯 α-LA 和 α-LA/CyD 纳米纤维的抗氧化活性。与纯 α-LA 相比，由于 CyD 包合物形成提高了水溶性，α-LA/CyD 纳米纤维具有更高的抗氧化性能。与纯 α-LA 相比，α-LA/CyD 纳米纤维在热处理（100°C 24 小时）下的热稳定性得到了提高。这些有希望的结果表明，抗氧化的 α-LA/CyD 纳米纤维可能具有作为口服速溶食品补充剂的潜在应用。
