0-acetyl-galactoglucomannan

Fig. 9. Partial structural formulas and shorthand notations for principal hemiceUuloses found in wood, where the sugar units ate noted as P-D-xylopyranose (Xylp), 4-Omethyl-a-D-glucopyranosyluronic acid (GlupU), a-L-arabinofuranose (Araf), P-D-glucopyranose (Glup), P-D-mannopyranose (Manp), and P-D-galactopyranose (Galp) for (a) arabino-4-O-methylglucuronoxylan from softwood, (b) 0-acetyl-galactoglucomannan from softwood, and...

Kg. 24. Partial chemical structure of some hemicelluloses A — 0-acetyl-(4-0-methyl-glucurono)xylan from hardwood B = arabino-(4-0-methylglucurono)xylan from softwood C = 0-acetyl-galactoglucomannan D = arabinogalactan from larch wood (138). 

Tenkanen, M., Thornton, J., and Viikari, L., An acetylglucomannan esterase of aspeigillus-oryzae-purification, characterization and role in the hydrolysis of O-acetyl-galactoglucomannan. J Biotechnol 1995,42 (3), 197-206. 

Acetyl derivative O-acetyl- galactoglucomannan (AcGGM) was prepared BSA Hydrogel Modified AcGGM decreased the hydrolysis rate and maximum hydrolysis, indicating steric hindrance of the enzyme by the acrylate side group. [141]... 

So far the aqueous fraction of the Organocell process seems to be a valuable source for an easy recovery of acetylated galactoglucomannan. The precipitated hemicellulose fraction was re-dissolved in citrate buffer pH 5 and incubated with purified xylanase (Fig. 2). Xylanase incubation led to the liberation of some xylose and xylo-oligomers (Fig. 3 buttom). The humpback present in the SEC elution curve (7.5 h) of the starting material may be derived from xylan impurities, since it disappeared after xylanase treatment. Therefore, specific xylanase treatment of the original hemicellulose solution prior to the precipitation seems to be the method of choice to obtain a pure acetylgalactoglucomannan. 

Isolation, Characterization, and Enzymatic Hydrolysis of Acetyl-Galactoglucomannan from Spruce (Picea abies)... 

Willfor, S., Rehn, P., Sundberg, A. et al. (2003) Recovery of water-soluble acetyl-galactoglucomannans from mechanical pulp of spruce. Tappi J., 2 (11), 27-32. 

We will discuss here an example which concerns kinetic modeling of hemicellulose O-acetyl-galactoglucomannan (Fig. 11.25) hydrolysis [4]. 

Shimizu, K., Teratini, F., Hashi, M. and Miyazaki, K. (1972). Effect of the thermal treatment on wood hemicelluloses. VI. Studies on the thermal analysis of arabinogalactan, and O-acetyl and deacetylated-galactoglucomannans. Mokuzai Gakkaishi, 18(2), 79-84. 

Similar structural problems exist for the distribution of side chains in galactoglucomannans, xyloglucans, arabinoxylans, and 4-0-methylglucuronoxylans, and even for the distribution of acetyl groups in glucomannans and for related features in many other polysaccharides. 

The main polyoses of softwoods are galactoglucomannan, with an average ratio of glucose to mannose of 1 3 and an average acetyl content of 1.3% (based on wood), and arabino-4-O-methylglucuronoxylan. 

Softwoods galactoglucomannan with 1.3 (%) acetyl hardwoods glucomannan. 6Softwood arabino-4-O-methylglucuronoxylan hardwoods 4-O-methylglucuro-noxylan with 4 (%) acetyl. 

Whatever the role of the 0-acetyl groups in wood, their presence seems to be of some importance to the tree, since the preponderant hemicellulose carries these groups, both in the gymnosperms and in the (botanically much younger) angiosperms— in the former, the galactoglucomannans, and in the latter, the xylan. 

As will be discussed later (see p. 473), the alkali-soluble glucomannans in softwoods have now been shown to be partially 0-acetylated in their native state. If the 0-acetyl groups in softwoods are associated only with the D-mannose-containing hemicelluloses, experimental data indicate that the galactoglucomannans must also carry 0-acetyl groups. This conclusion is strengthened by the fact that the extracellular galactoglucomannans are partly 0-acetylated. 

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