Influence of cyclodextrin complexation on the photodegradation and antioxidant activity of alpha-tocopherol

The influence of complexation with beta-cyclodextrin (beta-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD) or hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD) on the antioxidant activity and light-induced decomposition of vitamin E (alpha-tocopherol) was investigated. The interaction of the vitamin with the cyclodextrins was ascertained by nuclear magnetic resonance spectroscopy. The photodegradation of alpha-tocopherol was examined in emulsion vehicles and was not significantly influenced by complexation with beta-CD (the extent of decomposition was 39.9% for the beta-CD complex compared to 47.2% for the free vitamin) whereas HP-beta-CD and HP-gamma-CD enhanced the light-induced decomposition of alpha-tocopherol (the loss of the vitamin reached 64.6% for the HP-beta-CD complex and 65.8% for the HP-gamma-CD complex). On the other hand, accelerated stability studies indicated that the degradation of non-irradiated alpha-tocopherol was reduced by complexation with HP-beta-CD or HP-gamma-CD. The radical scavenging activity of alpha-tocopherol was evaluated in vitro using the xanthine/xanthine oxidase enzymatic system. No significant differences were observed between the free form of the vitamin and its complexes with beta-CD, HP-beta-CD or HP-gamma-CD. Therefore, complexation of alpha-tocopherol with these cyclodextrins does not interfere with the vitamin antioxidant activity.