Curdlan Gum

Source

Structural unit

Molecular structure

Functionality

Source

Curdlan gum is a microbial fermentation extracellular 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 beta-D glucan

Curdlan gum is an a moderate molecular weight (DP~450) unbranched linear 13 β-D glucan (M.Wt. ~100K) with no side-chains. [Back to Top ]

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 ]

Functionality

Curdlan gum is tasteless and produces 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 13 β-D glucan but has additional 16 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 (Chime). [Back to Top ]

Footnotes

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