(70s) Self-Assembly of Biopolymer Gel Networks within Hydrating Particles

Biopolymers provide a renewable source of structuring and controlled release agents for a variety of potential uses, and are commonly encountered in food, pharmaceutical, agricultural and other applications that require bio-compatibility. Swollen particulate forms of gelled biopolymers are particularly useful as they combine macroscopic structure formation with an ability to flow and often have a highly prized soft solid texture (in e.g. food applications), all at high water contents (>95%). Swollen biopolymer particles are readily prepared through chemical cross-linking of biopolymer chains (e.g. chromatography beads or modified starches), but the same type of material is difficult to prepare from the all-natural components which are increasingly desired in applications.

We now describe the production of dried amorphous particle forms of natural gelling biopolymers (polysaccharides and proteins), that when introduced to aqueous environments swell but are prevented from dissolving by a gelation driving force. This results in the formation of stable hydrated particles whose degree of swelling can be controlled and is dependent on the relative strengths of driving forces towards hydration/dissolution and cross-linking/gelation.

Major attractions of this approach are the elements of control, flexibility and applicability that are brought through the use of a spray-dried intermediate. Thus, for a given dried intermediate, the extent of swelling on re-hydration can be controlled by the relative strengths of osmotic hydration and gelation driving forces under the aqueous environment selected (temperature/solutes etc). Conversely, for given aqueous re-hydration conditions, dried particle compositions can in principle be designed to give desired swelling properties for e.g. structuring or molecular release properties. The diversity of gelation conditions for natural biopolymers provides a wide range of options to design compositions for desired functionalities.

We describe studies of representative gelling biopolymers (alginate, pectin and carrageenan) which illustrate the principles of controlled re-hydration from spray-dried amorphous particulates. The production and characterisation of the particles, the effect of solvent conditions on rehydration, and possible applications will all be discussed.