From holocellulose

For the study of soluble polysaccharides, a treatment with diluted TFA is sufficient and the reaction time can be kept short (7). Soluble polysaccharides of wood are separated from holocellulose by extraction with alkali. Wise et al. (10) term the extract with 5% KOH polyoses (hemicelluloses) A. Polyoses A can be hydrolyzed completely with 2N TFA within 1 hr. The chromatograms of the hydrolysates of polyoses A from spruce and beech holocelluloses recorded with a sugar analyzer (Biotronik ZA 5100) are shown in Figure 1. 

It should be noted that, during methylation, there is a selective loss of hemicellulose rich in galactose residues.148 In most studies on hemicelluloses, the materials extracted from holocellulose by alkali are recovered by mild acidification, followed by addition of an excess... 

In one case, the alpha-cellulose residue from a holocellulose preparation has been studied by methods which yield information concerning structure (see page 295). It is to be hoped that work of this kind will be continued and, further, that the techniques of structural carbohydrate chemistry will continue to be applied to the elucidation of the nature of the hemicellu-losic fractions which may be obtained so readily from holocellulose prepara-... 

Carbohydrate Analysis of Alpha-cellulose Prepared from Holocellulose... 

Isol. from holocellulose of Sphagnum moss, possibly present in other plants. Hygroscopic cryst. (EtOH aq.) (as Ca salt). [a]o +25 (c, 3.25 in H2O, equilib.). Not well characterised. Unprecedented type of struct, but see 5-C-Hydroxyido-pyranuronic acid, H-151. 

Figure 6. The rate of isothermal heat evolution on linear and logarithmic scales versus the reaction time for a 2.8 mm hardboard of holocellulose pulp. Released heat 1.0 kcal equal to 4.19 kJ. (Reproduced with permission from ref. 10. Copyright 1989 De Gruyter.)...

Prior to xylan removal it is possible to extract from the plant material those hemicelluloses soluble in dilute alkali. Soluble hemicelluloses of this type are the principal impurities extracted with xylan and consist for the most part of low molecular weight polysaccharides and polyuronides. Corn cob holocellulose may be freed of these compounds (called hemicellulose-B fraction, see Figure 2) by extraction with potas-... 

Relatively pure xylan isolated from the holocellulose of aspen (Populus) wood is said to contain 85% of xylose residues.78 One of the characteristic properties of xylan is its ease of hydrolysis. Because it hydrolyzes much more readily than cellulose, mild acid treatment may be employed to bring about preferential hydrolysis of xylan from plant material. Xylose is ordinarily prepared in the laboratory by direct sulfuric acid hydrolysis of the native xylan in ground corn cobs.74 Hydrolysis in hydrochloric acid proceeds rapidly, but decomposition to furfural also occurs to some extent.76 A commercial method for the production of D-xylose from cottonseed hulls76 and straw77 and from corn cobs17 78 has been described. 

Natural xylan may occur partially esterified with acetic acid. This possibility arises from the observation that most holocellulose preparations contain a small amount of acetic acid. So far, however, it has not been established which polysaccharides are esterified. Treatment of the holocellulose with the alkaline solutions necessary for xylan extraction brings about complete deacetylation. 

Partially degraded cellulose is called hydrocellulose or oxycellulose, depending on the agent used for degradation. The term holocellulose is used to describe the residue after lignin has been removed from wood pulp. 

When the hyper-cellulolytic mutant T. reesei QM9414 was grown on various substrates derived from wheat straw in stirred batch culture, the highest specific growth rates were on holocellulose and the hemicellulose-A defined by O Dwyer (8) it grew poorly on lignocellulose. By contrast,... 

Table I. Growth of Trichoderma reesei QM9414 (Tr) and T. harzianum IMI275950 (Th) on wheat straw lignocellulose (lignocell.) or derived cellulosic materials from straw (cell., cellulose hemicell-A, hemicellulose-A holocell., holocellulose)...

Holocellulose Cellulosic material obtainable from wood after removal of lignin. The term therefore means total carbohydrates (cellulose and hemicellulose) present in the wood (Refs 1 2) Ritter (Ref 3) succeded in isolating holocellulose from wood pulp by repeated chlori-nations, followed by extraction with alcohol containing 3% of monoethanolamine. The resulting product was white but changed color on standing... 

Table I. Hydrolysis of Polyoses A from Spruce Holocellulose with 72(%) Sulfuric Acid and 2N TFA6...

The whole procedure normally takes about 1 hr. The acid is then evaporated, and the dry matter can be analyzed. This method can be applied to cellulose from wood, as a-cellulose or pulp, or to other celluloses (e.g., cotton) as well as to cellulosic materials with higher amounts of other polysaccharides (e.g., holocellulose). The chromatograms of the hydrolysates of a-cellulose from beechwood and of holocellulose from sprucewood (Figure 6) are examples of the application of this method. Compared with sulfuric acid hydrolysis, the total sugar yield from the spruce holocellulose is higher after the hydrolysis with concentrated TFA (Table II). Regarding the individual sugars, it can be seen that the... 

Table II. Hydrolysis of Holocellulose from Spruce With 72(%) Sulfuric Acid° and 100(%) TFA6...

Figure 6. Chromatograms of the hydrolysates of a-cellulose from beech-wood and holocellulose from sprucewood...

Sprucewood holocellulose was treated with an endo-p-1,4-mannanase isolated from Aspergillus niger and an endo-/3-1,4-xylanase, two avicelases, and a cellobiohydrolase C isolated from Trichoderma viride. The mannanase hydrolyzed about a quarter of the mannan in 2-3 days without xylan or cellulose degradation. The xylanase hydrolyzed about half the xylan with 10% mannan solubilization. The three cellulases hydrolyzed up to 45% of the cellulose and 20% of the xylan, accompanied by 40-70% solubilization of the mannan. Combined xylanase-mannanase treatment hydrolyzed about half the xylan and mannan. Addition of mannanase to to cellulose-treated samples increased the degradation of the cellulose and mannan. Micromorphological studies of the variously treated specimens revealed a loss of substances in P/Slf T, and adjacent zones of S2 of the tracheid wall. 

Figure 2. Sugars from sprucewood holocellulose treated with mannanase for 80 hr. (For separation and detection method see Figure 1).

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