Novel single probiotic encapsulation by covalent nanocoating of azobenzene modified β-glucan for enhanced gastrointestinal stability and colonic targeted release

The purpose of this research was to investigate the application of azobenzene modified polysaccharide on the single probiotic encapsulation by carbodiimide-mediated amidation and evaluate its targeted delivery potential in colon. Yeast β-glucan (YBG) was first modified by azobenzene groups via esterification (AA-YBG), which was then conjugated to the amino groups on the Escherichia coli Nissle 1917 (EcN) surface membrane through carbodiimide-mediated amidation, resulting in the successful fabrication of single probiotic microcapsules (EcN@AA-YBG). SEM and TEM showed that AA-YBG formed a nano-sacle intact thin film on the surface of EcN through covalent coupling between amino groups on the EcN membrane and the carboxyl groups in AA-YBG molecular chains as evidenced by FT-IR, and the biocompatibility analysis showed that AA-YBG coupled nanolayer has no significant effect on the proliferation of probiotics. In vitro gastrointestinal digestion showed that compared to the free EcN which suffered structural disintegration and lost all the viability within 0.5 h of gastric acid digestion, the EcN@AA-YBG maintained robust structural integrity with viability above 77% after the entire 6 h of digestion. Colonic targeted release analysis revealed that EcN@AA-YBG not only susceptible to enzymatic cleavage by colonic azo reductase and hypoxic colonic condition, triggering the rapid release of probiotics in colon, the adhesion of EcN@AA-YBG to colon mucosa was significantly improved as well. Furthermore, due to the compact and intact surface nanocoating of AA-YBG, the resistance of EcN@AA-YBG to high temperature, antibiotics and reactive oxygen species conditions were all improved significantly.