The cell release kinetics and the swelling behavior of physically crosslinked xanthan–chitosan hydrogels in simulated gastrointestinal conditions

Abstract

Xanthan gum and chitosan can form physically crosslinked hydrogels of high swelling capacity. Xanthan–chitosan polyelectrolyte complex gels have been studied as microcarriers mostly for the encapsulation of enzymes while the studies on the applicability of the system for bacterial cells are scarce. In this work, probiotic bacteria were encapsulated in xanthan–chitosan gels. The main goal of this study was to characterize the swelling and the release behaviors of xanthan–chitosan hydrogel system under simulated GI-tract conditions to be able to assess its potential as an enteric delivery system for probiotics. We found that the cell release in simulated gastric fluid (SGF) at pH 2.0 for 2 h was negligible, and the complete release of the cells from the capsules in simulated intestinal fluid (SIF) was achieved in 5 h. The pH of the SGF solution was found to be more critical in determining the release properties of the capsules than the presence of the enzyme. The cell release kinetics under GI-tract conditions was also characterized. Cell release from xanthan–chitosan capsules in SIF (after 2 h exposure to SGF at pH 2.0), exhibited a Super Case II transport mechanism regardless of the formulation used, meaning that the chain relaxation is the driving mechanism for the release. Moreover, xanthan–chitosan capsules were found to swell by a diffusion-controlled mechanism. Additionally, cell viability study showed that xanthan–chitosan encapsulation provides a good protection for the probiotics. These results may suggest that xanthan–chitosan capsules have a good potential for the delivery of the probiotics to the intestines.