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Major carbohydrates in pectins:
GalA-GalA linkages are diaxial
⇒
structure similar to G-blocks in alginate
⇒
binds Ca
++
, leading to gelation
GalA-Rha and Rha-GalA
are also diaxial
O
COOH
OH
OH
OH
HO
α
-D-Galacturonic acid (GalA)
O
O
HO
OH
COOH
O
4
C
1
(1,4-linked)
O
COOCH
3
OH
OH
OH
HO
O
O
HO
OH
COOCH
3
O
4
C
1
(1,4-linked)
α
-D-Galacturonic acid (GalA) methyl ester ('methoxyl')
O
O
OH
H
OH
H
H
H
OH
CH
3
OH
OH
H
H
OH
H
HO
HO
H
H
H
3
C
4
C
1
unstable
1
C
4
α
-L-Rhamnose
(6-deoxy-L-mannose)
O
CH
3
OH
OH
HO
OH
= linkage in pectins