192
At lower pH, concentrations and in presence of divalent cations (calcium and zinc),
alginates form strong heat stable solution of high viscosity and exhibit Newtonian
behavior whereas solution exhibits pseudoplastic behavior at higher concentration.
In external gelation method, alginate microparticles are fabricated by the process of
water-in-oil emulsion and maintained by surfactants like Tween
®
80 and usually
calcium chloride in a solution form is added to the emulsion. The internal gelation
is very rarely used for microencapsulation purposes in which calcium carbonate is
used and is fabricated by the process of water-in-oil emulsion followed by addition
of organic acids like acetic acid. Calcium and carbonic acid are formed, when it
penetrates into water phase. The major drawbacks associated with alginates are
leaching of encapsulating agent during preparation and rapid dissolution in intestinal pH or in the presence of sodium ions and in most of the cases concentration
range of 0.5–4% are used and recommended for nano delivery. Besides this, there
are various downsides associated with alginate micro-particles such as liable to be
influenced to acidic conditions and also splitting and loss of mechanical stability in
these conditions, which worsen in the presence of monovalent ions or chelating
agents. The highly porous nature consequently results in fast diffusion of moisture
and other fluids through beads. To overcome the problem associated with mechanical stability of alginate microspheres, alginate in combination with other natural
and artificial hydrocolloids are used and also ionically cross-linked by addition of
divalent cations in aqueous solution. Properties like mild gel setting conditions,
biocompatibility, biodegradability, pH sensitiveness, low cost and mucoadhesive
property of alginates make it suitable for use as an effective matrices for the entrapment and/or delivery of variety of biological agents.
Gellan Gum
Gellan gum which is produced by fermentation using Sphingomonas paucimobilis
is a high molecular weight anionic linear polysaccharide. This polymer is a tetra
saccharide repeating unit of D-glucose, L-rhamnose and D-glucuronate in a molar
ratio of 2:1:1 and its molar mass is in the range of 5 × 10
5
g/mol. The 3-linked glucose units are substituted with glyceryl at O(2) and with acetyl at O(6). It can,
therefore, be designated as →4)-l-rhamnopyranosyl-a-(1 → 3)-d-glucopyranosylb-(1 → 4)-d-glucuronopyranosyl-b-(1 → 4)-d-glucopyranosyl-b-(1→). The gellan
gum chemically is composed of 60% glucose, 20% glucuronic acid and 20% rhamnose and has broadly been divided into three types on the basis of amount of acetyl
groups i.e. native gellan gum, deacetylated gellan gum and clarified gellan gum.
Gellan gum has been accepted as a food additive by the USA in 1992 proceeded by
EU approval as E 418 and followed by Canada, Australia and South Africa.
P. Chatur et al.
At lower pH, concentrations and in presence of divalent cations (calcium and zinc),
alginates form strong heat stable solution of high viscosity and exhibit Newtonian
behavior whereas solution exhibits pseudoplastic behavior at higher concentration.
In external gelation method, alginate microparticles are fabricated by the process of
water-in-oil emulsion and maintained by surfactants like Tween
®
80 and usually
calcium chloride in a solution form is added to the emulsion. The internal gelation
is very rarely used for microencapsulation purposes in which calcium carbonate is
used and is fabricated by the process of water-in-oil emulsion followed by addition
of organic acids like acetic acid. Calcium and carbonic acid are formed, when it
penetrates into water phase. The major drawbacks associated with alginates are
leaching of encapsulating agent during preparation and rapid dissolution in intestinal pH or in the presence of sodium ions and in most of the cases concentration
range of 0.5–4% are used and recommended for nano delivery. Besides this, there
are various downsides associated with alginate micro-particles such as liable to be
influenced to acidic conditions and also splitting and loss of mechanical stability in
these conditions, which worsen in the presence of monovalent ions or chelating
agents. The highly porous nature consequently results in fast diffusion of moisture
and other fluids through beads. To overcome the problem associated with mechanical stability of alginate microspheres, alginate in combination with other natural
and artificial hydrocolloids are used and also ionically cross-linked by addition of
divalent cations in aqueous solution. Properties like mild gel setting conditions,
biocompatibility, biodegradability, pH sensitiveness, low cost and mucoadhesive
property of alginates make it suitable for use as an effective matrices for the entrapment and/or delivery of variety of biological agents.
Gellan Gum
Gellan gum which is produced by fermentation using Sphingomonas paucimobilis
is a high molecular weight anionic linear polysaccharide. This polymer is a tetra
saccharide repeating unit of D-glucose, L-rhamnose and D-glucuronate in a molar
ratio of 2:1:1 and its molar mass is in the range of 5 × 10
5
g/mol. The 3-linked glucose units are substituted with glyceryl at O(2) and with acetyl at O(6). It can,
therefore, be designated as →4)-l-rhamnopyranosyl-a-(1 → 3)-d-glucopyranosylb-(1 → 4)-d-glucuronopyranosyl-b-(1 → 4)-d-glucopyranosyl-b-(1→). The gellan
gum chemically is composed of 60% glucose, 20% glucuronic acid and 20% rhamnose and has broadly been divided into three types on the basis of amount of acetyl
groups i.e. native gellan gum, deacetylated gellan gum and clarified gellan gum.
Gellan gum has been accepted as a food additive by the USA in 1992 proceeded by
EU approval as E 418 and followed by Canada, Australia and South Africa.
P. Chatur et al.