Fiber hemicellulose

A possible arrangement of cellulose fibers, hemicelluloses, and pectic materials in a cell wall has been proposed (Fig. 4-14). 

The galactan of Strychnos mix vomica,in which D-galactose is mainly (1— )-linked, showed an anticipated, weak cross-reaction in anti-Pn XIV. However, Heidelberger and colleagues considered that the d- and L-gal-actose residues (2 parts in 33), present as nonreducing end-groups in corn-fiber hemicellulose - must be very favorably situated in the molecule, since it precipitated 20% of the Type XIV antibody. 

The most commercially feasible hydrolysis method is the initial hydrolysis at 140°C for 30 minutes. This method hydrolyzes most of the starch and 72% of the hemicellulose. This leaves the cellulose and a portion of the hemicellulose to act as a carrier for the corn steep liquor and stillage to make corn gluten feed. The additional acid hydrolysis step creates a large amount of degradation products, which would be inhibitory to the ethanol fermentation, without giving a greater monosaccharide concentration. The enzyme hydrolysis step is not feasible without enzymes that contain activities specifically for the corn fiber hemicellulose matrix. These types of enzymes are not commercially available, or would be prohibitively expensive, therefore, enzyme hydrolysis of corn fiber is not currently commercially feasible. 

Potential resources of xylans are by-products produced in forestry and the pulp and paper industries (forest chips, wood meal and shavings), where GX and AGX comprise 25-35% of the biomass as well as annual crops (straw, stalks, husk, hulls, bran, etc.), which consist of 25-50% AX, AGX, GAX, and CHX [4]. New results were reported for xylans isolated from flax fiber [16,68], abaca fiber [69], wheat straw [70,71], sugar beet pulp [21,72], sugarcane bagasse [73], rice straw [74], wheat bran [35,75], and jute bast fiber [18]. Recently, about 39% hemicelluloses were extracted from vetiver grasses [76]. 

The number of reports about hemicelluloses that have been covered by this review indicates the significantly increased importance of all types of hemicelluloses as plant constituents and isolated polymers during the last decade. Attention has been paid not only to known hemicelluloses but also to the primary structure, physicochemical, physical, and various functional properties of hemicelluloses isolated from hitherto uninvestigated plants. The efforts to exploit a variety of plant as potential sources of hemicelluloses were pointed out particularly for agricultural crops, wood wastes, as well as for by-products of pulp and rayon fiber technologies. Many studies were devoted to characterize seed-storage hemicelluloses from plants that have been traditionally applied in food and medicine of many underdeveloped countries to find substitutes for imported commercial food giuns. 

NORMAND F L, ORY R L, MOD R R (1987) Binding of bile acids and trace minerals by soluble hemicelluloses of rice The ability of rice fiber components to bind bile acids may play a role in lowering serum cholesterol. Food Technology, 41(2) 86-90. 

TAKENAKA s (1992) Hemicellulose in rice bran fiber reduces thymus atrophy in rats treated wih bis-tri-n-butyn oxide. Chemosphere, 25(3) 327-34. 

Wood coatings, exterior, 28 67-68 Woodell s hardness scale, 2 3, 4 selected materials, 2 3t Wooden barrels, as industrial materials packaging, 18 8-9 Wood fibers, 22 173, 22 1-4 Wood hemicelluloses, sugar moieties of, 22 9... 

Water-holding capacity of hemicelluloses (contained in wheat brans and psyllium fiber) and celluloses may decrease mouth to rectum transit time, increase fecal weight, and decrease intraluminal pressure (36). These characteristics might be expected to interfere with calcium absorption decreasing time allowed for intestinal absorption, by diluting the concentration of calcium and... 

Various solvents are being investigated to dissolve lignocellulosic materials. Some approaches focus on the selective depolymerization and extraction of lignin and hemicellulose as pre-treatment to produce clean cellulose fibers for subsequent fermentation or for pulping. Other approaches attempt to dissolve the whole lignocellulose with or without depolymerization. The liquefaction processes that are carried out at high temperature (>300 °C), and produce a complex oil mixture, are discussed above with the pyrolysis processes. 

Beall, F.C. (1969). Thermogravimetric analysis of wood hgnin and hemicelluloses. Wood arui Fiber, 1(3), 215-226. 

For monitoring the extent of polysaccharide hydrolysis, l.c. methods that sepeu ate and analyze the non-fermentable oligosaccharides (d.p. 3-30) derived from cellulose, hemicellulose, and pectins are useful, and have already been described (see Section III,l,c). For determination of the monosaccharide composition of completely hydrolyzed, plant polysaccharides, l.c. is especially useful and has been applied to the compositional analysis of hydrolyzed plant fiber,wood pulps,plant cell-walls,and cotton fibers.In these representative examples, the major sugars of interest, namely, glucose, xylose, galactose, arabinose, and mannose, have traditionally been difficult to resolve by l.c. The separa-... 

Other abundant carbohydrates, such as hemicelluloses and pectin, are usually highly branched and thus not very suitable for fiber and film production. Hemicelluloses and some pectins are also acetylated in the native state, which makes them more resistant to enzymatic hydrolysis (20,21) and changes their solubility properties (9-77,75). Branching does not, however, preclude their utilization in such potentially large markets as thickeners and adhesives. Xylans, for example, show such a strong adhesion to cellulose fibers that they are very difficult to remove completely by both acidic and alkaline pulping processes (22). 

---