Controlled release of anthocyanins from oxidized konjac glucomannan microspheres stabilized by chitosan oligosaccharides

A novel oxidized konjac glucomannan (OKGM) microsphere system was developed to protect and targeted deliver the sensitive antioxidant-anthocyanins into intestine. The microspheres were made of oxidized konjac glucomannan, which was cross-linked by Fe³⁺ via emulsification method. The absorption of anthocyanins was driven by the electrostatic interaction between the negatively charged OKGM microspheres and positively charged anthocyanins. CLSM images showed that anthocyanins distributed homogenously through the OKGM microspheres. The absorption and release behavior of anthocyanins on OKGM microspheres were determined as a function of pH and salt concentration. A maximum absorption capacity was obtained at pH 3 and low salt concentration. However, anthocyanins were released significantly at simulated stomach conditions due to fast degradation of OKGM microspheres. An extra positively charged chitosan oligosaccharides (COS) layer was applied on OKGM microspheres to prevent H⁺ ions permeating into microspheres under stomach condition. COS oligomers were cross-linked withglutaraldehyde to further strengthen the OKGM microspheres' structure. Finally, glutaraldehyde cross-linked COS stabilized OKGM microspheres became stable against H⁺ ions in simulated stomach condition, therefore OKGM microspheres can prevent an early release of the anthocyanins in stomach condition and achieve a sustained released in the intestinal condition. The invitro release experiments revealed that the OKGM microspheres had a potential as a carrier of targeted delivery of bioactive compounds in the intestine.