Hemicelluloses are heteropolysaccharides formed by a main chain of aldose molecules (glucose, galactose, xylose, or mannose) linked by β-1→4 bonds, with multiple branches or side chains of arabinose, galactose, and glucuronic acid.
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From: Medical Biochemistry, 2017
M.T. Holtzapple, in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003
Hemicellulose is a major component of plant cell walls, which are well described in the CELLULOSE article. Figure 5 shows the distribution of lignin, cellulose, and various hemicelluloses in the cell wall layers for both softwoods and hardwoods. (The distribution in herbaceous crops would be similar to hardwoods.) Hemicellulose is the dominant carbohydrate in the compound middle lamella, whereas cellulose is more plentiful in the secondary layers (S1, S2, and S3). In hardwoods (and herbaceous crops), glucuronoxylan is the primary hemicellulose, whereas glucomannan is more prevalent in softwood.
Figure 5. Distribution of lignin, cellulose, and hemicellulose in (a) hardwood and (b) softwood. Data sources: (1) Meier H (1964) In: Zimmerman MH (ed.) The Formation of Wood in Forest Trees. New York: Academic Press; (2) Panshin AJ, de Zeeuw C (1970) Textbook of Wood Technology, 3rd edn, vol. 1. New York: McGraw-Hill. Reproduced from Hemicelluloses, Encyclopaedia of Food Science, Food Technology and Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993, Academic Press.
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F.G. Huffman, in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003
Hemicellulose is a branched polymer of pentose and hexose sugars, found in the plant cell wall. The uronic acid composition is mainly d-glucuronic acid and 4-O-methyl-d-glucuronic acid. There are two distinct hemicelluloses in plants: the acidic and the neutral. Acidic hemicelluloses contain a larger number of uronic acids than neutral hemicelluloses. Hemicelluloses are partially fermented by the microorganisms of the colon, producing some volatile fatty acids. Hemicelluloses are insoluble in water but soluble in alkaline solutions. They, along with other insoluble dietary fibers, decrease the intestinal transit time; hemicelluloses also increase fecal weight and slow down starch hydrolysis. Acidic hemicelluloses may bind to cations. These characteristics of hemicellulose may be responsible for its physiological effects.