Glucomannan (GM) a water-soluble polysaccharide possesses mannose residues which are extracted from tubers, bulbs, softwoods and roots of many plants. Glucomannan is considered to be a dietary fibre which is actually present in some plant species in the form of hemicelluloses component in the cell wall. Its structure consists of linear chain of mixed residues of α-1,4 linked D-mannose and D-glucose monomers arranged in blocks. The molecular weight of native GM lies between 1×104– 2×106. Low molecular weight GM could be obtained by de-polymerization technique. The average molecular weight of Konjac Glucomannan (KGM) is 500,000 – 2,000,000 and varies with species, growing area, storage time and processing methods. The glucomannan from different sources vary in its mannose to glucose ratio. Konjac tuber glucomannan has a molar ratio of 1.6:1 or 1.4:1 (ratio differs with konjac breeds), Orchid tubers and Scotch pine have molar ratios of 3.6:1 and 2.1:1 respectively. Diversity of glucomannan also depends on degree of acetylation in GM chain. Values of degree of acetylation are 5to10% or every 19th sugar residue (attached randomly at C-6 position in KGM), is actually responsible to facilitate dispersion and solubility by inhibiting the intra-molecular hydrogen bonds. This solubility function is attractive for multiple pharmaceutical applications. However increase in acetylation degree in GM slows the gelation process. The intrinsic viscosity of KGM solution is highest among the polysaccharides that facilitate swelling behaviour and hence gel formation that finds application in food industry. Gels have good stability, films, hydrogel, beads, micro and nanoparticles of Glucomannan may have potential usage in therapeutic drug delivery systems without causing toxicity. It may also be useful in treatment of chronic constipation, decreasing serum cholesterol, and increasing insulin sensitivity. As a food supplement it could play a significant role in weight loss. Carboxymethylated glucomannan improves the properties of paper, such as burst index, dry tensile index, and wet tensile index. These diverse applications make Glucomannan a most sought after biomolecule.
GM is considered as a dietary fibre
The diversity of glucomannan depends on degree of acetylation in GM chain. Generally the acetylation degree values are 5 to 10% or of the every 19th sugar residue (attached randomly at C-6 position in KGM), actually facilitates dispersion and solubility by inhibiting the intra-molecular hydrogen bonds. This solubility function is attractive for multiple pharmaceutical applications. However, increase in acetylation degree in GM slows down the gelation process.
The molecular weight of native GM lies between 1×104 to 2×106, and average molecular weight of KGM is 500,000–2,000,000. The molecular weight varies with species, growing area, storage time and processing methods. Low molecular weight GM could be obtained by de-polymerization. The intrinsic viscosity of KGM solution is highest among the polysaccharides. This property facilitates swelling behavior and gel formation. The gels have good stability and are generally thermo irreversible.
Glucomannan finds major application in food industry as a food additive as emulsifying agent and thickening agent. It has been reported that GM properties such as emulsification, suspension, stabilization and thickening are pH dependent. For example KGM possess water retention, suspension, and stabilization properties at pH less than10.
Gelation and high viscosity are the prominent properties of glucomannan that can be utilized in food industry, such as thickener in the syrup, jelly, edible film, noodle, and binder in sausage as reported for GM from
Glucomannan is a soluble fiber and it has been examined for the treatment of constipation. Glucomannan may relieve constipation by decreasing fecal transit time.
Glucomannan significantly improve the total cholesterol in obese patients.
Glucomannan can also be used as therapeutic adjunct for type 2 diabetes. It has been found to improve the lipid profile and alleviate the fasting blood glucose levels in type 2 diabetics.
The use of glucomannan for weight loss has given mixed results.
It has been reported that films, hydrogel, beads, microparticles and nanoparticles of Glucomannan may have potential usage for drug delivery systems without causing toxicity. KGM is used in drug delivery system, for bio-adhesive properties, improvement in cellular therapy and as gel filler material in prosthetic implants in pharmaceutical industry.
In the lower gut fermentation of glucomannan dietary fiber can produce short chain fatty acid (SCFA). Previously reported studies prove that in case of konjac glucomannan there was increase in acetic acid, propionic acid, and butyric acid content both in in vitro and in vivo.
Polysaccharides of glucomannan may be hydrolysed to lower molecular weight molecules by the action of acids or enzymes specifically mannanases or cellulases. The hydrolysates produced from konjac glucomannan by the two enzyme systems mannanase and cellulase is effective for stimulating the growth of lactic acid bacteria.
The symbiotic ability of probiotic bacteria and konjac glucomannan hydrolysates (GMH) to inhibit acne-inducing bacterium, Propionibacterium acnes growth was studied in vitro. All strains of probiotic bacteria were tested. They all were able to inhibit the growth of this species of skin bacterium where the inhibition was significantly (P<0.01) enhanced by the presence of the GMH prebiotic. As the current treatment of acne is based on topical or systemic drugs, it is worth examining further the bio-therapeutic activities of the GMH and selected probiotics with a view to future use as prophylactic or therapeutic synbiotics for treating acne infections.
Glucomannan and its derivatives combine with natural or synthetic polymers to boost up the desired properties of polymer. Chitosan and alginate are now the two most frequently studied polymers for blends.
The previously reported study demonstrated that carboxymethylated glucomannan could improve the paper properties. Addition of 0.9% carboxymethylated glucomannan significantly increased the density, burst index, tensile index, folding endurance of paper. Polyamide-epichlorohydrin (PAE) is found to improve the wet strength of paper. Combination of 0.6% PAE and 0.6% carboxymethylated glucomannan increase the burst index, dry tensile index, wet tensile index of paper by 14.1%, 25%, 34.3%, respectively, as compared to that of the control, where there is decrease in the folding endurance. The dry tensile index and wet tensile index were increased with increasing the carboxymethylation time of glucomannan. When the carboxymethylation time was 40 min, these properties were increased by 13.4% and19.3%, respectively, as compared with that of the 25 min carboxymethylation time. The results indicated that PAE and carboxymethylated glucomannan had a synergistic effect. SEM analysis showed that paper strengthening agent could increase the combination of fibers in paper.
Carboxymethyl modification of konjac glucomannan affects water binding properties. The water binding properties of konjac glucomannan (KGM) and carboxymethyl konjac glucomannan (CMKGM) has various applications in food, pharmaceutical, and chemical engineering fields. The equilibrium moisture content of CMKGM was lower than that of KGM at the relative humidity in the range 30–95% at 25℃. The water absorption and solubility of CMKGM in water were lower than that of KGM at 25℃. Carboxymethyl modification of KGM reduces the water adsorption, absorption and solubility. Both carboxymethylation and deacetylation could confer hydrophobicity to CMKGM.
Primary root and tuber crops starchy roots, tubers, rhizomes, corms and stems have high water content (70-80%). These crops contain mainly carbohydrates (largely starches that account for 16-24 percent of their total weight) with very little protein and fat (0-2% each). It is used mainly for human food (as such or in processed form), for animal feed and for manufacturing starch, alcohol and fermented beverages including beer (http://www.fao.org). For economic and commercial benefits there is a need to separate out the biomolecules; evaluate its nutritional importance as well as study for other diverse industrial applications.