Galactomannan structure

The possibility of there being branches in the mannan main-chain should not be excluded. Estimates from a number of methylation analyses of galactomannans have shown a slightly higher molar quantity of 2,3-di-O-methyl-D-mannose than 2,3,4,6-tetra-O-methyl-D-galactose53 78,79. However, if branching of the mannan main-chain is a feature of galactomannan structure, its extent seems to be fairly low. 

Reprinted from Fluorescence Microscopy to Study Galactomannan Structure in Frozen Sucrose and Milk Protein Solutions Copyright 1999 with permission from Elsevier, )... 

Fig. 25. Representation of the galactomannan structure. represents the C-6 position where —OH can be specifically modified.

Evans, A.J. Hood, R.L. Oakenfull, D.G. Sidhu, G.S. (1992). Relationship between structure and function of dietary fibre a comparative study of the effects of three galactomannans on cholesterol metabolism in the rat. British Journal of Nutrition, Vol.68, No.l, (July 1992), pp. 217-229, ISSN 0007-1145. 

The general chemistry of the galactomannans has been reviewed by Whistler and Smart" and others,7 " and papers frequently appear that discuss the uses of guar and locust-bean gums in various industrial applications, such as in cosmetics9 and food.10,11 Most of this article deals with investigations of the structural chemistry of galac-... 

In describing and interpreting some of the more important properties of plant galactomannans, comparisons will be made with structurally similar polysaccharides, including the closely related glucomannans and galactoglucomannans, and those based on (1 — 4)-/3-D-xylan main-chains (for example, the arabinoxylans) and (1 — 4)-/3-D-glucan main-chains [for example, the amyloids and sodium 0-(carboxymethyl)cellulose]. 

From Centrosema plumari has been isolated50 an unusual polysaccharide containing 92% of D-galactose and only 8% of D-mannose the structure of this mannogalactan obviously cannot conform to that of the normal, seed galactomannan. 

In a similar series of experiments, Unrau and Choy59 found that the structure of Caesalpinia pulcherima galactomannan differs from the normal type of structure, but to a much lesser extent —4% of the D-mannose units in the main chain are /3-D-(l — 3)-linked, and 2% are ( 1 — 2)-linked. Smith degradation again indicated that isolated and consecutive /8-D-(l — 3)-linkages were present in the main chain. 

Although most of the galactomannans studied are reported to have structures based on a completely /3-D-(l — 4)-linked backbone having single a-D-galactosyl stubs attached to this backbone by (1 — 6)-linkages, the reports just discussed indicate that deviations, sometimes substantial, can occur. Indeed, it is possible that deviations from the classical type of structure, to the extent shown by Caesal-... 

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