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1.2.5. Examples: Composition of
some algal alginates
8
The following table shows the composition of alginate from various seaweeds
used for industrial production of alginates:
Source
F
G
F
M
F
GG
F
MM
F
GM,M
G
F
GGG
F
GGM
F
MGM
N
G>1
Durvillea antarctica
0.32
0.68
0.16
0.51 0.17
0.11
0.05
0.12
4
Saccharina japonica
0.35
0.65
0.18
0.48 0.17
Ascophyllum
nodosum
0.39
0.61
0.23
0.46 0.16
0.17
0.07
0.09
5
Lessonia nigrescens
0.41
0.59
0.22
0.40 0.19
0.17
0.05
0.14
6
Laminaria digitata
0.41
0.59
0.25
0.43 0.16
0.20
0.05
0.11
6
Macrocystis pyrifera
0.42
0.58
0.20
0.37 0.21
0.16
0.04
0.02
6
L. hyperborea
leaf
L. hyperborea
stipe
0.49
0.63
0.51
0.37
0.31
0.52
0.32
0.26
0.19
0.11
0.25
0.48
0.05
0.05
0.13
0.07
8
15
Alginates from kelp (
M. pyrifera
) and
A. nodosum
have nearly identical
content of L-guluronic acid (ca. 40%), but the former has slightly longer G-
blocks, giving stronger (stiffer) gels with Ca
++
. The stipe of
L. hyperborea
has
alginate with very long G-blocks, making it one of the best gelling alginates.
For this reason the alginate industry separates the stem and the leaf and
produces alginates in separate production lines.
Ultralong G-blocks in algal alginates:
Recently (2013) a novel enzymatic tool (specific alginate lyases) has been
applied to study not only the average G-block length, but also the distribution
of block lengths (figure below)
The G-blocks from L. hyperborea stipe, having an average G-block length
(N
G>1
) (according to the table above) of 15 has in fact a trimodal distribution
consisting of primarily short blocks (DP 2-4), a small amount of blocks in the
range 5-20, and interestingly, a major proportion (ca 50%) with DP above 20-
30). The presence of ultralong G-blocks in some alginates and their role in
gelation is currently studied.
8 Adapted from: Draget, K. I., Moe, S. T., Skjåk-Bræk, G., and Smidsrød, O. (2006) Alginates, In Food
Polysaccharides and Their Applications (Stephen, A. M., Phillips, G. O., and Williams, P. A., Eds.) second ed., pp
289-334, CRC Press, Boca Raton