2009_Book_FoodChemistry

4.4 Polysaccharides 305
water extraction under mild alkaline conditions,
followed by drying or isolate precipitation.
4.4.4.3.2 Structure, Properties
Carrageenans are a complex mixture of various
polysaccharides. They can be separated by
fractional precipitation with potassium ions.
Table 4.20 compiles data on these fractions
and their monosaccharide constituents. Two
major fractions are κ (gelling and K + -insoluble
fraction) and λ (nongelling, K + -soluble).
The sequence favors the formation of a doublestranded
helix (Fig. 4.19). λ-Carrageenan
contains as the basic building block β-D-
Galp-(1 → 4)-α-D-Galp (cf. Formula 4.139),
which is joined through a 1,3-glycosidic linkage
to the polymer. Position 6 of the second galactose
residue is esterified with sulfuric acid as is ca.
70% of position 2 of both residues. The high
sulfate content favors the formation of a zigzag
ribbon-shaped conformation.
Table 4.20. Building blocks of carrageenans
Carrageenan
κ-Carrageenan
κ-Carrageenan
λ -Carrageenan
µ-Carrageenan
ν-Carrageenan
Furcellaran
Monosaccharide building block
D-Galactose-4-sulfate,
3,6-anhydro-D-galactose-
2-sulfate
D-Galactose-4-sulfate,
3,6-anhydro-D-galactose
D-Galactose-2-sulfate,
D-galactose-2,6-disulfate
D-Galactose-4-sulfate,
D-galactose-6-sulfate,
3,6-anhydro-D-galactose
D-Galactose-4-sulfate,
D-galactose-2,6-disulfate,
3,6-anhydro-D-galactose
D-Galactose-D-galactose-
2-sulfate, D-galactose-4-sulfate,
D-galactose-6-sulfate,
3,6-anhydro-D-galactose
(4.139)
The molecular weights of κ-andλ-carrageenans
are 200–800 kdal. The water solubility increases
κ-Carrageenan is composed of D-galactose, 3,6-
anhydro-D-galactose and ester-bound sulfate in
a molar ratio of 6:5:7. The galactose residues are
essentially fully sulfated in position 4, whereas
the anhydrogalactose residues can be sulfated
in position 2 or substituted by α-D-galactose-6-
sulfate or -2,6-disulfate. A typical sequence of
κ-(orι-)carrgeenan is:
(4.138)
Fig. 4.19. ι-Carrageenan conformation. a Double helix,
b single coil is presented to clarify the conformation
(according to Rees, 1977)