Xylan VOLUME

Interactions with xanthan were investigated for some GAX fractions of wheat bran [109]. Whereas, for lowly substituted GaMs a synergy in viscosity was observed at low total polymer concentrations, yielding a maximum of the relative viscosity at nearly equal proportions of both polysaccharides [124], the xanthan/xylan mixtures at the same experimental conditions showed no synergy. The observed decrease in the relative viscosity values upon addition of the xylan indicates that a certain interaction with xanthan takes place, but that it leads to a contraction in the hydrodynamic volume. The authors suggested that structural and conformational differences between GaM and GAX might be the reason for this observation. 

Fig. 7 Stabilization effect of various xylan types isolated from beech wood (GXl and GX2), corn cobs (AGXl), rye bran (AXRl and AXR3), and corn hulls (AXCl and AXC2) on the protein (BSA) foam against thermal disruption foam volume before (V1) and after (V2) heating at 95 °C for 3 min [128]...

Koch-Light 1887-00 oat-spelt xylan (Lot 90560) was split into soluble and insoluble fractions by dissolving it in 0.05A/, pH 6.05 sodium citrate buffer and centrifuging out Ae unAssolved material. The msoluble portion was suspended in Ae buffer in roughly 1% concentration and was assayed wiA an equal volume of Xylanase II in... 

Furoic acid (furan-2-carboxylic acid, or pyromucic acid) is used as a bactericide, and the furoate esters are used as flavoring agents, as antibiotic and corticosteroid intermediates. It is obtained by the enzymatic or chemical/catalytic aerobial oxidation of furfural (2-furalaldehyde) the latter is the only unsaturated large-volume organic chemical prepared from carbohydrates today. D-Xylose and L-ara-binose, the pentoses contained in the xylan-rich portion of hemicelluloses from agricultural and forestry wastes, under the conditions used for hydrolysis undergo dehydration to furfural. 

The enzymatic hydrolysis of soluble birchwood xylan was carried out as follows The substrate (0.5 g) was placed universal or phosphate buffer in 500 mL conical flasks, and 1500 U of crude xylanase was added to start the reaction, for a total volume of 25 mL. The hydrolysis and control reactions were accomplished at the same conditions described for enzymatic hydrolysis of lignocellulosic materials. 

The second class comprises conventional solids, defined by a chemical formula, but whose property requirements are very minimal. In this class we included lignin, cellulose, mannan, galactan, xylan, arabinan and the biomass. The properties specified in the database include molecular weight, heat of formation, solid molar volume, and solid heat capacity. 

In Volume 33 of this Series, we presented1 a review of the crystalline structures of polysaccharides published during the period 1967-1974. Detailed accounts of progress in structural studies on specific types of polysaccharides were presented in the Proceedings of the Twenty-sixth Symposium of the Colston Research Society and were subsequently published as a book.2 Precise methods for X-ray diffraction analysis of biopolymer structures were discussed by Hukins.3 The aspects of the structures of cellulose, mannan, and xylan, their organization in the cell wall, and the biosynthesis of cell-wall polysaccharides were described by Mackie.4 Work on the structures of the connective-tissue polysaccharides, O-acetylcellulose, and the various forms of amylose was reviewed by Atkins,5 Chanzy,6 and Sarko,7... 

Coarsely ground corn cobs or crude xylan can be used as starting materials. The xylan in either source is hydrolyzed with 7% (v/v) sulfuric acid by refluxing for 2.5 h. The mixture is filtered through cloth on a Buchner funnel with as much liquid as possible obtained by suction. The residue is washed with an equal volume of water by suspension as thin slurry and then filtered. A few drops of 1-octanol are added to the combined filtrates that are neutralized with barium carbonate. The solids (primarily barium sulfate) in the mixture are filtered and the residue washed by suspension in water and filtered. If corn cobs are used as the starting material. 

It is clear that chemical evidence is, at present, available both for and against a branched framework in softwood glucomannans. It was mentioned (Part I, p. 286) that (4-0-methylglucurono)xylans and cellulose apparently occupy a similar hydrodynamic volume in solution. In view of this fact, it appears fairly safe to assume that the same should apply to the glucomannans, which are structurally much closer to cellulose than... 

Although reaction in JV,N-dimethyIformamide greatly facilitates methylation, the method suffers from the limitation that it often gives low recoveries of methylated polysaccharides, and the effectiveness of the methylation appears to depend on the volume of N,M-dimethylformamide used. Even with monosaccharides, incomplete methylation has been reported. D. A. Rees and coworkers have given detaUs of a modified Kuhn methylation for carrageenan, and they also described the methylation of dextran and of a xylan from red seaweed in N-methyl-2-pyr-rolidinone. A micro Kuhn method suitable for oligosaccharides has been described by Perila and Bishop. ... 

The liquor was neutralised using acetic acid and slowly precipitated in the threefold volume of ethanol. The pH was adjusted to 5.5 and the precipitate was recovered by filtration. The xylan was re-dispersed in water, the volume equivalent to the volume of the starting liquid. The solution was re-precipitated in the threefold volume of ethanol, the pH adjusted to 4.0 and the precipitate recovered by filtration. The xylan was washed first with ethanol and then with ether. Samples were dried in the fume hood from ether. During this procedure the particles size was reduced every now and then to insure the formation of a fine powder. 

An experiment was carried out in an ideal batch reactor operating isothermally at 98 °C. At the begirming of the experiment, 8 g of com cob (dry basis) was placed in the reactor and 100 ml of H2SO4 solution (3.00 g/100 ml) was added to the reactor. The xylan content of the feed material was 42 wt% based on dry material. There was no xylose or furfural in the com cob. (Assume that the com cob dissolves completely and that the volume of solution after the com cob is dissolved is the same as the volume of the dilute H2SO4. You also will have to assume that the mass of xylose formed is equal to the mass of xylan hydrolyzed.) How much time is required to reach 90% conversion of xylan What are the mass concentrations of xylose and furfural at this time ... 

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