The cell release kinetics and the swelling behavior of physically crosslinked xanthanechitosan hydrogels in simulated gastrointestinal conditions Sanem Argin a, * , Peter Kofinas b , Y. Martin Lo a a Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, USA b The Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA article info Article history: Received 5 August 2013 Accepted 28 February 2014 Keywords: Xanthan gum Chitosan Hydrogel Super Case II mechanism Encapsulation Probiotic bacteria abstract Xanthan gum and chitosan can form physically crosslinked hydrogels of high swelling capacity. Xanthan echitosan 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 xanthanechitosan gels. The main goal of this study was to characterize the swelling and the release behaviors of xanthanechitosan hydrogel system under simu- lated 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 charac- terized. Cell release from xanthanechitosan 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, xanthanechitosan capsules were found to swell by a diffusion-controlled mechanism. Additionally, cell viability study showed that xan- thanechitosan encapsulation provides a good protection for the probiotics. These results may suggest that xanthanechitosan capsules have a good potential for the delivery of the probiotics to the intestines. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Hydrogels are three-dimensional networks of natural or syn- thetic polymers with the ability of absorbing water (Hennink & van Nostrum, 2002; Kim, La Flamme, & Peppas, 2003). They have gained attention in biomaterials research due to their biocompat- ibility with tissue and blood (Hoffman, 2002; Lee & Mooney, 2001; Slaughter, Khurshid, Fisher, Khademhosseini, & Peppas, 2009). One of the main areas that the hydrogels find application is the controlled release of the molecules and cells (Cook, Tzortzis, Charalampopoulos, & Khutoryanskiy, 2011; Costa, Valente, Miguel, & Queiroz, 2011; Peppas, Bures, Leobandung, & Ichikawa, 2000; Rao & Taguchi, 2011; van Tomme et al., 2005). Hydrogels can be formed by physical or chemical crosslinking. When sub- jected to water, both chemically and physically crosslinked hydro- gels swell due to the solvent penetration. Physically crosslinked hydrogels will eventually degrade in solvent resulting from the swelling stress whereas chemically crosslinked hydrogels stay intact unless covalent bonds are broken with certain treatments (Hennink & van Nostrum, 2002; Rao & Taguchi, 2011). Xanthan gum and chitosan are two natural polymers that are capable of forming physically crosslinked hydrogels with reversible ionic linkages (Berger et al., 2004; Magnin, Lefebvre, Chornet, & Dumitriu, 2004). These hydrogels can absorb large quantities of water, many times more than their dry weight (Argin-Soysal, Kofinas, & Lo, 2009). Xanthan gum is a microbial exopoly- saccharide consisting of a cellulosic backbone with side chains of two mannose and one glucuronic acid on every second glucose residue (Jannson, Kenne, & Lindberg, 1975; Melton, Mindt, Rees, & Sanderson, 1976). Due to the presence of glucuronic acid and py- ruvate in its side chains, xanthan gum is considered to be an anionic polyelectrolyte (Richardson & RosseMurphy, 1987). For this reason, * Corresponding author. Permanent address: Department of Food Engineering, Yeditepe University, 34755, Atasehir, Istanbul, Turkey. Tel.: þ90 216 578 10 91; fax: þ90 216 578 04 00. E-mail addresses: sanem.argin@yeditepe.edu.tr (S. Argin), kofinas@umd.edu (P. Kofinas), ymlo@umd.edu (Y.M. Lo). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd http://dx.doi.org/10.1016/j.foodhyd.2014.02.018 0268-005X/Ó 2014 Elsevier Ltd. All rights reserved. Food Hydrocolloids 40 (2014) 138e144