pH-Dependent Release Property of Agar Beads Containing Chitosan Particles

Abstract

Agar beads containing chitosan particles were prepared by dropping hot suspension of agar/chitosan (2/1, w/w) into cold distilled water. The bead size was 2–3 mm and the cross section of the bead revealed a porous structure on FE-SEM (Field Emission Scanning electron microscopy) photos. The pH-dependent release property of the bead was observed using either blue dextran or FITC-dextran (Fluorescein isothiocyanate-dextran) as a dye. The % releases of blue dextran for 6 h were 42% at pH 3.5, 48% at pH 5.5 and 52% at pH 8.0. Obviously, the release was significantly suppressed at acidic pHs. This is possibly because the positive charge intensity of chitosan becomes stronger at an acidic pH. As a result, it tends to interact with negatively charged blue dextran, leading to a suppressed release at acidic pHs. On the other hand, the % releases of FITC-dextran for 6 h were 88% at pH 4.5, 80% at pH 5.5 and 76% at pH 8.0. The release was somewhat promoted at acidic pHs. At an acidic pH such as pH 3.5, chitosan could be dissolved within agar beads, giving rise to cavities. In addition, there might be no electrostatic interaction between positively charged chitosan and neutral FITC-dextran. Therefore, FITC-dextran would readily release through the cavities, resulting in a higher release at an acidic pH.

Keywords:

• Agar
• chitosan
• bead
• blue dextran
• FITC-dextran
• pH-sensitive release

Acknowledgements

This work was supported by a grant (20060024) from Special fisheries Research program Ministry of Marine Affairs & Fisheries, Republic of Korea.