(22b) 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.