Cryotropic Gel Formation for Food Nutrients Encapsulation - a Controllable Processing of Hydrogel By Freezing

Abstract

Considering severe security regulations for food and pharmaceutical ingredients, it would be ideal to make various types of encapsulants from a widely approved single substance. Use of cryogels for encapsulation would be an interesting idea. Cryogel is defined as a hydrogel where sol-gel transitions are induced by localized concentration increase of the substrate due to ice formation during freezing. It would thus be expected that gel network formations can be controlled by a freezing process, and the controlled polymeric structures are advantageous for release control. In this work, chitosan based cryogels were prepared for investigating encapsulation characteristics of a model ingredient. It was found that the release behaviour of the ingredient from the prepared cryogel matrix could be controlled by the freezing condition for the gel preparation, indicating that a freezing operation controlled the gel network formation that determined consequent release characteristics from the hydrogel matrix. The differences of gel network structures formed via the different freezing conditions were illuminated by SAXS analysis. A clear structural anisotropy appeared when the chitosan suspension was rapidly frozen. On the other hand, this strong anisotropy disappeared when the cooling rate was decreased. It is a clear evidence of polymeric structural modifications appeared in cryogels prepared via different cryo-processing. This cryogel based encapsulation would be a potential technique for realizing a structural design of the encapsulants simply by tuning the freezing conditions.