Hemicellulose apparent

Figure 1. Effects of water-washing on the quantity of nicotine (O), protein (A), and apparent hemicellulose ("Al in the fibrous residue of Ky 171 tobacco.

Attempts to remove hemicellulose for production of dissolving pulps with very low hemicellulose contents have shown that complete enzymatic hydrolysis of hemicellulose within the pulp is difficult to achieve. The xylan content in delignified mechanical aspen pulp was reduced from approximately 20 to 10%, whereas in bleached hardwood sulphite pulp the xylan content was decreased from 4 to only 3.5% even at very high enzyme dosages (50). The complete removal of residual hemicellulose seems thus unattainable, apparently due to modification of the substrate or to structural barriers. 

The apparent difference between viscosity average (M ) and number average molecular weight (M ) for unfractionated triacetate samples and high molecular weight fractions may be attributed to the presence of hemicellulose and polydispersity effect in these materials as shown in the table in question and in Figure 3. 

The cuticular fraction (10-12%) of the cell walls has not received much attention, nor has the part (55-70%) which is usually called hemicellulose. Carlier and Buffel34 found nearly 50% more pentosan (measured as furfural) in potato tuber treated with 1-naphthaleneacetic acid at 10 mg. per liter in agar pectin increased in almost the same proportion, and in proportion to the increased intake of water starch decreased by 36%, apparently to provide the substrate for increased respiration. 

Analyses of the hemicelluloses of woods indicate the presence of a high proportion of D-xylose residues in association with those of a methyl ether of a hexuronic acid.64 The first evidence for the chemical structure of such wood xylans came from the isolation of xylobiose, xylotriose,65 and the aldobiouronic acid 0-(4-0-methyl-a-D-glucosyluronic)-(l —> 2)-D-xylose acid (IX)22 from partial hydrolyzates of aspen wood. The role of such oligosaccharide fragments in wood xylans became more apparent as the result of a study of a xylan from European beechwood,26 in which it was shown... 

Disordered cellulose molecules as well as hemicelluloses and lignin are located in the spaces between the microfibrils. The hemicelluloses are considered to be amorphous although they apparently are oriented in the same direction as the cellulose microfibrils. Lignin is both amorphous and isotropic. 

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