Polysaccharides play a role in emulsions in three main ways:
1. Polysaccharides increase the viscosity of the continuous phase of the emulsion.
One of the main functions of polysaccharides in emulsions is to thicken the
continuous liquid. The intended effect is usually to impart a desired texture
(increase viscosity or stiffness to the system and reduce buoyancy-driven
creaming or sedimentation of the emulsion droplets and other particles in the
system). Because of their highly swollen molecular structure in solutions,
leading to a high effective volume fraction at low concentrations, most
polysaccharides are very effective in providing a high viscosity at low
concentration.
2. Polysaccharides flocculate the droplets into a gelled droplet network. In a
solution of gelling polysaccharide (e.g. alginates, pectin, K-carrageenan), the
formation of bonds between segments of the different polysaccharide molecules
in solution can lead to formation of a space-filling network of biopolymer
molecules. The binding regions in the gelled polysaccharides are often highly
structured regular chain conformations, such as double helices, bundles of
double helices, egg-box, and double helix-ribbon configurations. A prerequisite
for gel formation is that the regular molecular segments are interrupted by
nonbonding sequences to form an open, water-holding structure. Such a network
can resist a finite applied stress, below which there is no discernable flow. On
increasing the applied stress, the structure is broken down, either at a molecular
level (related to an apparent yield stress) or at a macroscopic level (related to
fracturing of the gel).
3. Some polysaccharides, such as starch granule and inulin, are in particulate form
and increase the viscosity of the emulsion by increasing the total volume fraction
of dispersed material.
2 Polysaccharides Used in Preparation of Micro- and
Nanoparticles
2.1 Chitosan
Chitosan, a biopolymer, has received ample attention and has been widely considered for micro- and nanoparticle preparation. It is the second-most abundant
naturally occurring polysaccharide. Properties like biodegradability, low toxicity
and good biocompatibility make it appropriate for biomedical and pharmacological
inventions and also for use in ophthalmology, anti-diabetic agents, antiinflammatory drugs and for immobilization of enzymes and proteins.
Generally, chitosan is formed of distributed β-(1–4)-linked D-glucosamine
(deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit), manufactured
by deacetylation of chitin extracted from shells of crabs, shrimps and krill. Chitosan
that is accessible commercially is deacetylated 66–95% and has an average
272
A.K. Anal and A. Tuladhar
1. Polysaccharides increase the viscosity of the continuous phase of the emulsion.
One of the main functions of polysaccharides in emulsions is to thicken the
continuous liquid. The intended effect is usually to impart a desired texture
(increase viscosity or stiffness to the system and reduce buoyancy-driven
creaming or sedimentation of the emulsion droplets and other particles in the
system). Because of their highly swollen molecular structure in solutions,
leading to a high effective volume fraction at low concentrations, most
polysaccharides are very effective in providing a high viscosity at low
concentration.
2. Polysaccharides flocculate the droplets into a gelled droplet network. In a
solution of gelling polysaccharide (e.g. alginates, pectin, K-carrageenan), the
formation of bonds between segments of the different polysaccharide molecules
in solution can lead to formation of a space-filling network of biopolymer
molecules. The binding regions in the gelled polysaccharides are often highly
structured regular chain conformations, such as double helices, bundles of
double helices, egg-box, and double helix-ribbon configurations. A prerequisite
for gel formation is that the regular molecular segments are interrupted by
nonbonding sequences to form an open, water-holding structure. Such a network
can resist a finite applied stress, below which there is no discernable flow. On
increasing the applied stress, the structure is broken down, either at a molecular
level (related to an apparent yield stress) or at a macroscopic level (related to
fracturing of the gel).
3. Some polysaccharides, such as starch granule and inulin, are in particulate form
and increase the viscosity of the emulsion by increasing the total volume fraction
of dispersed material.
2 Polysaccharides Used in Preparation of Micro- and
Nanoparticles
2.1 Chitosan
Chitosan, a biopolymer, has received ample attention and has been widely considered for micro- and nanoparticle preparation. It is the second-most abundant
naturally occurring polysaccharide. Properties like biodegradability, low toxicity
and good biocompatibility make it appropriate for biomedical and pharmacological
inventions and also for use in ophthalmology, anti-diabetic agents, antiinflammatory drugs and for immobilization of enzymes and proteins.
Generally, chitosan is formed of distributed β-(1–4)-linked D-glucosamine
(deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit), manufactured
by deacetylation of chitin extracted from shells of crabs, shrimps and krill. Chitosan
that is accessible commercially is deacetylated 66–95% and has an average
272
A.K. Anal and A. Tuladhar