Isolation of hemicelluloses

Hardwood xylans and xylans of annual plants may contain up to 7% O-bound acetyl groups. Seven out of ten xylose residues in native hardwood xylan are acetylated on C-2 and/or C-3 (10). Because of the possible migration of O-acetyl groups between 2- and 3-positions during and after isolation of hemicellulose components, it is difficult to determine their original distribution in nature (11). The ratios reported for 2-, 3-, and 2,3-positions of acetyl groups in birch xylan have been 2 4 1 (3) and 2 2 1 (10) and in bracatinga xylan 3 3 1 (12). 

Simonson, R. (1963). The hemicellulose in the sulfate pulping process, Part 1, The isolation of hemicellulose fractions from pine sulfate cooking liquors. Sven. Papperstidn. 66, 839-845. 

In the isolation of hemicelluloses from plant materials containing a relatively large amount of pectic substances, such as the cambium layer of a wood or the leaves and stems of plants, the water-soluble materials and insoluble pectic substances are first removed. The hemicelluloses are then extracted by an alkaline solution. Sodium hydroxide solutions at concentrations varying from 2 to 17% have been used for this purpose. Norman recommends a 2% solution of sodium carbonate when high purity is more desirable than completeness of extraction. Most investigators have used a cold sodium hydroxide solution of approximately 4% concentration. " ... 

In the isolation of hemicelluloses from plant materials containing relatively large amounts of hemicelluloses and small amounts of insoluble pectic materials, as in hardwoods, the powdered material is first extracted with organic solvents and hot water. The hemicelluloses are then removed by two extractions with a cold 4% solution of sodium hydroxide. The material is made neutral with dilute hydrochloric acid and washed with water. It is then extracted successively with a hot. 05 N solution of hydrochloric acid and a cold 5% solution of ammonium hydroxide. This procedure removes only a part of the hemicelluloses and pectic materials from a wood since lignin protects the underlying hemicelluloses from the alkaline solution or is combined with them. - To overcome this difficulty the wood is suspended in water and treated with chlorine gas. - - The subsequent addition of a large volume of... 

A new approach to the isolation of hemicelluloses is through the production of holocellulose by chlorination of the wood followed by extraction of the holocellulose with a 3% solution of ethanolamine in alcohol. The holocellulose contains the carbohydrate portion of the wood freed of lignin. Hemicelluloses are then extracted from this product in the regular way. " ... 

Before methyl sulfoxide became available, several attempts were made to use liquid ammonia for the isolation of hemicelluloses from wood. The use of this solvent was introduced by Yan and Purves, and the method was subsequently applied in isolating xylans from sugar maple and trembling... 

Several studies have been conducted for the separation of hemicellulose from different plant byproduct with different methods of isolation. Lignification process conducted among others by NaOH in 70% ethanol, chlorine, sodium hypochlorite and 30% H2O2. Isolation of hemicellulose used alkaline compounds such as KOH and NaOH with various concentrations, whereas HCl and 90% ethanol is used for the purification of hemicellulose [39,40,57]. 

The isolation of hemicellulose from various materials that have lygnocellulose has been done by several researchers. Numerous researchers have studied the different procedures, solvents, working conditions, and hemicellulose extraction processes. Various procedures have been developed for the isolation of hemicellulose, using sodium and potassium hydroxide, peroxide hydrogen and a base, or with a solution of barium or calcium hydroxide with a wide range of temperatures [7, 9,14, 22, 25, 39, 40]. 

Different separation and purification procedures have been proposed to isolate hemicelluloses from different raw materials. Extraction of hemicelluloses from different resources has been studied since a long time ago. Isolation of hemicelluloses using cost efficient extraction methods would be beneficial to increase the utilization of hemicelluloses. Alkaline aqueous solutions and organic solvents have been used to extract hemicelluloses from the original or delignified wood [holocellulose] [1,9,21,25,31,33,34,5 7]. 

Muchlisyam et al. [33, 34] worked for the isolation of hemicellulose from corn cobs to made eco-friendly waste and its use to reduce cadmium and plumbum from rabbit s blood [33,34]. 

Isolation of hemicellulose fractions. A standard mediod for R/S-fraction determination (13) was adapted and conducted as follows Pulp samples were swollen for 2 min in aqueous sodium hydroxide solution (10 or 18%), then pulped for 3 min and incubated for 60 min at 20 °C. Next, the slurry was separated by filtration into die alkali-insoluble R-fiaction and the alkali-soluble S-fraction. For quantitative separation of the beta-cellulose, fractionation was done by precipitation widi sulphuric acid and subsequent centrifiigation, gamma-cellulose remained in the filtiate. 

Bian, J., Peng, F, Peng, X. -R, Xu, F., Sun, R. -C., Kennedy, J. F. Isolation of hemicelluloses from sugarcane bagasse at different temperatures Structure and properties. Carbohydrate Polymers 2012, 88,638-645. 

Persson, T., Nordin, A.-K., Zacchi, G. and Jonsson, A.-S. (2007) Economic evaluation of isolation of hemicelluloses from process streams from thermomechanical pulping of spruce. Appl. Biochem. BiotechrwL, 136-140, 741-752. 

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