0-Glucomannans

Next to the hardwood xylans, the softwood glucomannans are, of the wood hemicelluloses, easiest to obtain in the pure state. This statement is 

The ease with which cellulose and glucomannan tend to associate is also evident from investigations on the acid sulfite cooking of wood. If such a 

A large number of methods have been used for isolating pure gluco-mannans from softwoods. One of the techniques most widely applied involves a pre-extraction of the holocellulose with 24% (5 N) aqueous potassium hydroxide solution for removal of the arabino-(4-0-methyl- 

The glucomannans obtained in this way are usually pure enough for structural investigations. Minor proportions of a contaminating xylan are readily removed by one or two purifications by way of the insoluble complex of the glucomannan with barium hydroxide. The copper complex may also be used for this purpose. i -  

Fractional precipitation of the acetate has been used successfully on several occasions for preparing a pure glucomannan,although one failure has also been reported. The method appears preferable to one involving the methyl ether.  

Polysaccharides based on D-mannose as the major structural unit occur in woods and in the seeds of many plants. Although polysaccharides from the latter sources are often classified as seed mucilages, this term is unsatisfactory and, in view of close similarities in structure, the two groups of polysaccharides may be considered together. 

Mannans and glucomannans from plant sources all contain linear chains of (1 — 4)-linked d-D-mannose and /J-D-glucose residues as their main structural features. The only true mannans (that is, polysaccharides containing 95% or more of D-mannose residues) so far examined from land plants are those from vegetable ivory (Phytelephas macrocarpa).90 96 The 

Two mannans may be isolated from ivory nuts. Mannan A, which is extracted with alkali, occurs in granular form,94 96 and x-ray diffraction photographs of both the native and the extracted polysaccharide show distinct crystalline patterns.96 Mannan B cannot, however, be extracted directly, and it is separated from cellulose by precipitation from cupram-monium solution.91 In the plant, mannan B is built up of microfibrils analogous to those of cellulose, but the extracted polysaccharide shows no tendency to crystallize on precipitation.95 

Although unresolved problems of fine structure still remain, no essential differences in chemical structure have yet been revealed between the two 

Clearly, two morphologically distinct mannans occur in ivory nuts, and, although both polysaccharides contain the same chemical features, there is evidence that they differ in molecular size. Thus, nitration of ivory-nut shavings followed by fractionation of the polysaccharide nitrates affords 

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Table 5. Comparison of Glucomannan Compositions from Various Sources...

Only traces of mannose occur in the hydrolysates of some monocotyledon stems (7,9) although glucomannans occur in the tubers and leaves of some monocotyledon species (72). 

Both types of xyloglucans exhibit monolayer sorption onto cellulose (116) and tamarind xyloglucan exhibits maximum specific sorption onto cellulose less than that of coniferous xylan. By inference with other data, this is also less than that of glucomannan and hardwood xylan, but similar to many additives used in the paper industry. 

CeU waUs of woods contain other subgroups of hemiceUuloses, in particular those composed primarily of D-mannopyranosyl or D-galactopyranosyl units. Glucomannans [11078-31-2] comprise 3—5% of the wood of angiosperms and 3—12% of the wood of gymnosperms. Galactoglucomannans [9040-29-3] are also common. 

P-D-mannan with single 6-Unked a-D-galactose branches g 4)-p -D-glucomannan ... 

Glucomannans (GM) and galactoglucomannans (GGM), common constituents of plant cell walls, are the major hemicellulosic components of the secondary cell walls of softwoods, whereas in the secondary cell walls of hardwoods they occur in minor amounts. They are suggested to be present together with xylan and fucogalactoxyloglucan in the primary cell walls of higher plants [192]. These polysaccharides were extensively studied in the 1960s [6,193]. 

The main side effects of glucomannan include flatulence and stomach discomfort. Glucomannan may also expand in the esophagus (swallowing tube) and cause blockage if it is not taken with plenty of water. It can also interact with other medicines it should be taken separately from other medicines by at least a couple of hours. 

Fig. 1. Global symptom score in patients treated with glucomannan plus rifaximin and in patients treated with glucomannan plus placebo (from Papi et al. [45]).

Similar results were obtained in a large prospective open trial including 968 outpatients with symptomatic diverticular disease [44], Patients were randomly assigned to receive fiber supplementation (glucomannan 4 g/day) or fiber supplementation plus rifaximin (400 mg twice a day for 7 days every month) for 12 months. After 12 months, 56.5% of patients in the rifaximin group were symptom free compared to 29.2% of patients in the fiber supplementation only group (p < 0.001). 

Although there is some evidence for the efficacy of long-term treatment with rifaximin for symptomatic relief in patients with uncomplicated diverticular disease, an unresolved issue is whether rifaximin can prevent major inflammatory complications of diverticular disease. In the two prospective open trials discussed above, the occurrence rate of complications in 12 months was lower in patients treated with glucomannan plus rifaximin compared to patients treated with glucomannan only 2.7 versus 0.9% [43] and 3.2 versus 1.3% [44], This observation was not confirmed in the double-blind placebo-controlled trial [45] in which no difference in the 1-year complication rate was observed between the rifaximin and placebo groups. However, in all the studies, the number of patients suffering complications in a 12-month period was too small to detect any statistically significant... 

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