Locust bean Gum structure
Locust bean gum is a linear consisting of β-(1,4)-D-mannose units. Approximately every fourth mannose units is substituted with a small side chain consisting of a 1,6 linked α-galactose sugar. The exact distribution of the sidechains has been the subject of a lot of study (McCleary) and the best description is probably using Markov chain extension statistics where the chain is built up from one end in a linear fashion and the presence of a galactose sidechain on a residue is determined by the presence or absence of any residues on the preceding two units.
Locust bean gum is very similar to other galactomannans. The main difference being the level of galactose sidechains present. The range extends from fenugreek, which is completely substituted to ivory nut mannan which is essentially unsubstituted.
|Galactomannan substitution levels|
|Ivory nut mannan||no galactose|
|Locust bean gum||1 galactose / 4 mannose|
|Tara gum||1 galactose / 3 mannose|
|Guar gum||1 galactose / 2 mannose|
|Fenugreek gum||1 galactose / 1 mannose|
The level of substitution has a major impact on the properties of the gums as polymannan can associate and self cross link. Hence ivory nut mannan can be completely insoluble whereas fenugreek shows the properties of a simple random coil. Locust bean gum shows intermediate properties in that it is soluble but shows substantial aggregation in solution.