PREPARATION of CORE-Shell Microparticles by Cryotropic Gelation of Chitosan-BASED Biopolymers

Preparation of core-shell microparticles by cryotropic gelation of chitosan-based biopolymers

Wiwut Tanthapanichakoon^1*,Kyuya Nakagawa²,

Nataporn Sowasod^3,4 and Tawatchai Charinpanitkul⁴

¹Department of Chemical Engineering, Tokyo Institute of Technology, Japan (Email: wiwutt@chemeng.titech.ac.jp)

²Research Centre for Nano-Micro Science and Engineering, University of Hyogo, Japan (Email: nakagawa@eng.u-hyogo.ac.jp)

³Nanoscience and Technology Program, Graduate School, Chulalongkorn University, Thailand (Email: noo_pun22@hotmail.com)

⁴Center of Excellence in Particle Technology, Faculty of Engineering, Chulalongkorn University, Thailand (Email: ctawat@chula.ac.th)

Abstract

In the last decades, nano-micro encapsulation technology has attracted deep interest from the food and pharmaceutical industries because of its versatile applications such as preservation of efficacy and controlled release of active food ingredients such as vitamin, polyphenol etc. (Lakkis, 2007). Hydrogel is often employed in the formation of shell matrix composed of semipermeable membrane envelope made via sol-gel transition around the encapsulated ingredients. The main disadvantage of the conventional hydrogel methods is the requirement of a cross-linking agent for gel formation, which could pose health hazard in food and pharmaceutical products. In addition, the gelation process is sensitive to changes in pH and temperature. These drawbacks of the conventional hydrogels can be circumvented by using cryotropic gelation, in which sol-gel transition is induced solely by localized concentration increase of the substrate due to ice formation during freezing (Lozinsky et al., 1986; Lozinsky & Damshkaln 2000, Giannouli, & Morris, 2003; Orrego, &, Valencia, 2009).

In the present study, the encapsulation of an oil-soluble food nutrient, curcumin, in hydrogels of natural polymer chitosan in the absence of any cross-linking agent was carried out by cryotropic gelation. A curcumin-loaded oil-in-water emulsion was prepared and incorporated into a polymeric suspension consisting of chitosan and a suitable ratio of κ-carrageenan and carboxy methylcellulose sodium salt (NaCMC). The encapsulation of curcumin in chitosan was achieved by converting the resulting colloidal suspension into hydrogels via cryotropic gel formation. The obtained frozen hydrogel samples were freeze-dried for preservation. Curcumin was subsequently extracted by immersion of the dried samples in a phosphate-buffered solution to determine the encapsulation yield in the matrix. The yield of curcumin encapsulation was investigated and found to depend on both the cooling rate and the ratio of κ-carrageenan to NaCMC. As the cooling rate increased, the encapsulation yield rose in tandem. Similarly, the release behavior of the encapsulated curcumin in an aqueous phase was investigated and shown to depend on the same two factors despite a difference in the oil-phase composition. Two types of release behavior were observed: a burst release and a moderate first-order release rate. In fact, when the ratio of κ-carrageenan to NaCMC was kept constant, the cooling rate was found to determine the type of release provided the ratio of κ-carrageenan to NaCMC was appropriate. Generally, the higher the number of cross-linkings in the polymer matrix and the stronger the bonding strength, the slower the release rate should become. A more balanced ratio of κ-carrageenan to NaCMC was shown to yield the first-order rate release and by implication a stronger microstructure.