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Alcaligenes faecalis

 

Alcaligenes faecalis, from  Centers for Disease Control and Prevention's Public Health Image Library

Curdlan Gum

Curdlan forms elastic gels, insoluble in cold water.

 

V Source
V Structural unit
V Molecular structure
V Functionality

Source

Curdlan is a microbial fermentation extracellular gum. It is a polymer prepared commercially from a mutant strain of Alcaligenes faecalis var. myxogenes. It is relatively expensive by weight but becoming rather less so.

Structural unit

1-3 β-D glucan

1-3 beta-D glucan

 

Curdlan gum is a moderate molecular mass (molecular weight) (DP~450) unbranched linear 1->3 β-D glucan (M.Wt. ~100K) with no side-chains.  [Back to Top to top of page]

Molecular structure

Curdlan gum has junction zones consisting of parallel in-phase triple right-handed six-fold helices (fibre repeat 18.78 Å) [503] forming an uncharged rigid rod-like conformation. The chains are held by intra-helix hydrogen bonding between the 2-OH groups; each such group hydrogen bonding by donation to one chain and acceptance from the other chain on the inside of the helix axis. As single-stranded curdlan forms a six-fold helix stabilized by a chain of intramolecular hydrogen bonds between neighboring 2-OH groups, the change from single to triple helices involves these 2-OH groups changing their hydrogen bonding allegiance from intramolecular to intermolecular.  [Back to Top to top of page]

Functionality

Curdlan gum is tasteless and produces a retortable freezable food elastic gels. It is insoluble in cold water a but aqueous suspensions plasticize and briefly dissolve before producing reversible gels (that is, curdling, hence its name) on heating to around 55 °C [504]. Heating at higher temperatures produces more resilient irreversible gels, which then remain on cooling, by the aggregation of the triple-helical structures and syneresis. The 'curds' consist of mixtures of single and triple helices. Salts tend to prevent curdlan from gelling and their presence weakens the final gels [504].

 

Scleroglucan (from Sclerotinia sclerotiorum) is also a 1->3 β-D glucan but has additional 1->6 β-links that confer solubility under ambient conditions but do not significantly interfere with a triple helix gelling process similar to curdlan. Similar polysaccharides can be also extracted from other sources such as waste yeast.

 

Interactive structures are available (Jmol).  [Back to Top to top of page]


Footnotes

a Curdlan is soluble in dimethylsufoxide [1457]. [Back]

 

 

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This page was established in 20032 and last updated by Martin Chaplin on 5 November, 2017


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