Methodology for Carbohydrates

Estimation of hemicelluloses



Hemicellulose are non-cellulosic, non=pectic cell wall polysaccharides. They are regarded as being composed of xylans, mannans, glucomannans, galactans and arabinogalactans. Hemicelluloses are categorized under ‘unavailable carbohydrates’ since they are not split by the digestive enzymes of the human system.





Principle

Refluxing the sample material with neutral detergent solution removes the water-solubles and


Materials over than the fibrous component. The left out material is weighed after filtration and expressed as neutral detergent fiber (NDF).



Material
» Neutral Detergent Solution
» Weigh 18.61g disodium ethylenediamine tetraacetate and 6.81g sodium borate decahydrate. Transfer to a beaker. Dissolve in about 200mL of distilled water by heating and to this, add a solution (about 100 to 200mL) containing 30g of sodium lauryl sulphate and 10mL of 2-ethoxy ethanol. To this add a solution (about 100mL) containing 4.5g of disodium hydrogen phosphate. Make up the volume to one liter and adjust the pH to 7.0.
» Decahydronaphthalene
» Sodium sulphite
» Acetone


Procedure
1.
To 1g of powdered sample in a refluxing flask add 10mL of cold neutral detergent solution.
2.
Add 2mL of decahydronaphthalene and 0.5g sodium sulphite.
3.
Heat to boiling and reflux for 60min.
4.
Filter the contents through sintered glass crucible (G-2) by suction and wash with hot water.
5.
Finally give two washing with acetate.
6.
Transfer the residue to a crucible, dry at 100°C for 8h.
7.
Cool the crucible in a desiccator and weigh.




Calculation

Hemicellulose = Neutral detergent fiber (NDF) – Acid detergent fiber (ADF)


Note
See Lignin for determining acid detergent fiber.




Reading

1. Goering, H D and Vansoest, P J (1975) Forage fiber analysis US Dept of Agriculture. Agricultural Research Service Washington.