Chemistry Reference
In-Depth Information
range of pH [
39
,
57
]. The seed gum can be isolated by the following procedure:
dried crushed seeds were extracted successively with light petroleum and ethanol to
defat and decolorize, respectively, then extracted with 1 % aqueous acetic acid and
extract was added slowly, with stirring to large excess of ethanol. The crude gum
was collected, washed with ethanol, and dried (yield 2.3 g/100 g) [
39
]. The seed
gum can be purified by barium complexing method [
58
].
5.2.2 Anionic Gums
A sort of gum contains anionic functional groups, such as -COOH, -SO
3
2
, etc.
attached on its backbone and carries negative charges. Different from the nonionic
gum without charges, the negatively charged functional groups of anionic gums
may bring better hydrophilicity, complexing capability to cations, responsive
behaviors to external stimulus, and higher reactive activity resulting from the
polar functional groups. Thus, the anionic gums were also developed as valuable
commercial polymer materials and found more expensive application in chemical
and industrial fields. Xanthan gum,
k
-carrageenan, psyllium, alginate, and acacia
gum are the representative sorts.
5.2.2.1 Xanthan Gum
Xanthan gum (XG) is an extracellular heteropolysaccharide of
Xanthomonas
campestris
. Structural unit of xanthan gum consists of
β
-(1-4)-
D
-glucopyranose glu-
can (as cellulose) backbone with side chains of
β
-(3-1)-
α
-linked
D
-mannopyranose-(2-
1)-
-
D
-mannopyranose on alternating residues (Fig.
5.4
)
[
59
,
60
]. It was the first fermentative biopolymer product based on corn sugar and
has attained commercial status. It can be used in food and pharmaceutical industry
because of the properties like thickening, emulsion stabilization, water binding,
suspending, and oil recovery [
61
-
64
]. Beside these usages, it has a drawback: it is
susceptible to microbial attack, which limits its use. Modification of XG by graft
copolymerization technique allows one to chemically change the polysaccharide chain
by introducing polymer chain that configures different structural characteristics to the
initial polymer.
β
-
D
-glucuronic acid-(4-1)-
β
5.2.2.2 k-Carrageenan (Also Called as Antlers Gum)
k-
Carrageenan is one of the nontoxic linear sulfated polysaccharides that are
obtained commercially by alkaline extraction of certain species of red seaweeds
(algae). The structure of
k
-carrageenan is made up of
α
-(1-4)
D
-galactose-4-sulfate
and
-(1-3) 3,6-anhydro-
D
-galactose (Fig.
5.5
)[
65
-
67
]. It is widely used as a
thickening, gelling, and stabilizing agent in food industry [
68
] as well as has
applications in pharmaceutical [
69
] and biotechnology sectors [
70
].
k
-Carrageenan
β
