Hemicellulose suspensions

The gel curves (Figures 5-11) were obtained by measuring the viscosity of hemicellulose suspensions while the temperature was increased at a rate of 1 °C/minute to approximately 90 °C. The hemicellulose mixture was then cooled at the same rate. 

An increase in pH of the hemicellulose solution thus clearly decreases the gelling temperature of the hemicellulose suspension. The gel curves of the... 

Figure 6. Gel curves of hemicellulose suspensions (15% solids) (2). The pH of the hemicellulose suspension solution was adjusted to pH 8.3 prior to drying and milling. The pH of the suspensions was adjusted as indicated.

If the borax is added to the hemicellulose suspension, the viscosity behavior differs substantially when compared with a hemicellulose suspension with the borax inside the hemicellulose particles. In Figure 11, the viscosity behaviors of two such suspensions are presented. The hemicellulose with the borax added to the suspension of hemicellulose powder clearly gels at a lower temperature. The viscosity upon cooling of this mixture is also much lower when compared with the hemicellulose with borax inside the powder particles. The sodium hydroxide added with the borax to the hemicellulose suspension again may have caused this phenomenon. 

Figure 7. Gel properties of hemicellulose suspensions (15% solids) at different pH s (5). The hemicellulose was treated with borax (2.0%) and the pH adjusted to 8.5 before drying and ball-milling. The pH of each suspension was adjusted as indicated.

Figure 8. Gel curves of hemicellulose suspensions (12.5% solids) containing different quantities of ash (>/). Each hemicellulose was treated with 2% borax and diluted with sulfuric acid to pH 7.5 to 8.0 before drying and ball-milling.

Figure 9. Gel curves of hemicellulose (14.8% ash) suspensions (12.5% solids) (5). The pH of the hemicellulose suspensions was adjusted to 9.7, or 5, and each treated with 2.0% borax on hemicellulose solids before drying and ballmilling.

Figure 11. Viscosity of hemicellulose suspensions (12.5% solids) (7) A, suspension of hemicellulose powder obtained from a solution of hemicellulose (14.8% ash) neutralized (pH 7), and mixed with borax (2.0%) before drying and grinding B, suspension of hemicellulose powder (4.8% ash) mixed with borax (2.0%) and sodium hydroxide (2.0%).

Our two network model of the primary wall receives support from a variety of indirect observations. For example it has been shown Aat when a cell wall is regenerated by a carrot protoplast a homogalacturonan/ rhamnogalacturonan shell is laid down first, through which the cellulose/ hemicellulose network is later intercalated (8). Further evidence that pectin may form an independent network is seen in the fact that walls from suspension-cultured cells of tofnato Lycopersicon esculentum VF 36),... 

Pretreatment of Substrate. Several different lignocelluloses were pretreated with NaOH. This pretreatment partially solubilizes the hemicelluloses and lignin and swells the cellulose so that the organism can utilize it for its growth and for production of a cellulase system in SSF. The treated lignocelluloses were not washed. The NaOH treatment is done with a minimum amount of water so that, after the addition of nutrient solution and inoculum, the moisture content is less than 80% wt/wt and there is no free water in the medium. More water was added to make suspensions of different lignocellulosic substrates of the desired concentration (1% or 5%) for liquid-state (submerged) fermentation (LSF). 

Darvill, J. E., McNeil, M., Darvill, A. G., Albersheim, P. (1980). Structure of plant cell walls XL Glucuronoarabi-noxylan. A second hemicellulose in the primary cell walls of suspension-cultured sycamore cells. Plant Physiol, 66,1135-1139. 

Corn stover, a well-known example of lignocellulosic biomass, is a potential renewable feed for bioethanol production. Dilute sulfuric acid pretreatment removes hemicellulose and makes the cellulose more susceptible to bacterial digestion. The rheologic properties of corn stover pretreated in such a manner were studied. The Power Law parameters were sensitive to corn stover suspension concentration becoming more non-Newtonian with slope n, ranging from 0.92 to 0.05 between 5 and 30% solids. The Casson and the Power Law models described the experimental data with correlation coefficients ranging from 0.90 to 0.99 and 0.85 to 0.99, respectively. The yield stress predicted by direct data extrapolation and by the Herschel-Bulkley model was similar for each concentration of corn stover tested. 

Ply Adhesion of Soda Bagasse Hemicellulose. First, various hemicellulose mixtures were evaluated solely on a ply adhesion basis. A suspension (15% solids) of hemicellulose, of a particle size below 0.2 mm, was prepared at ambient... 

The viscosities of the three hemicellulose adhesives and the starch control are given in Figure 4. The viscosity of the suspended hemicellulose adhesive was lower when compared at different solids contents than that of the starch control. It was, on the other hand, much higher than the viscosity of a raw starch suspension (30 cP at 35% solids). The higher viscosity of the raw hemicellulose adhesive is probably caused by the gel-like outer layer of the raw hemicellulose-suspended particles. The suspended starch particles showed no such surface gel effect, but remained totally undissolved. The viscosities of the cooked and raw-cooked hemicellulose adhesive were similar to those of the starch adhesive (Figure 4). 

Bagasse hemicellulose samples (32% ash and 12% lignin) were dissolved in water and the pH adjusted with dilute sulfuric acid to 4.6, 7.5, 10, and 12 (no pH change). The neutralized samples were dried and ground to particles below 0.2 mm. A suspension of each at 15% solids was heated at a constant rate of approximately 1 °C/minute to approximately 90 °C, after which the solutions were cooled at the same rate to ambient temperature. The viscosities of the mixtures were determined after short intervals and are illustrated in Figure 5. 

In Figure 9, the gel curves of purified hemicellulose treated with borax and acid to obtain different pH s before drying are illustrated. These curves are almost identical over a wide pH range. The main difference is the temperature where the viscosity of the suspension starts to increase. This temperature increases with a decrease in pH. The temperature of complete gelling, as indicated by the maximum temperature during the heating stage, increases from 72 °C at pH 9 to 78 °C at pH 5. 

Suspension-cultured tissues of cereal endosperm Cells containing mainly primary cell walls Hemicelluloses (mainly acidic arabinoxylans and p-D-glucans) cellulose, some phenolics and phenolic esters, and proteoglycans... 

A 10% wheat bran suspension in water was autoclaved for 30 min at 115 °C and the resulting soluble (liquor) and insoluble components (residue) were separated by filtration. The liquor and residue fiactions were then used alone or mixed with 1 % MCC as carbon sources for P. decumbens growth. The biomass in cultures grown on wheat-bran liquor plus MCC was less than that on wheat-bran residues plus MCC, but the cellulase activity released was higher (Fig. 4). The liquor apparently contained a factor that stimulated cellulase synthesis and/or secretion. In contrast, the xylanase activity in the supernatants of cultures supplemented with wheat-bran liquor was lower than that in cultures supplemented with the wheat-bian residues, which were in consistent with the residues having higher hemicellulose content. 

The procedure is carried out with 50 g of corn cobs powder, which was added to 500 ml of 0.03 M NaOH in 70% ethanol and heated at 60°C and stirred for 2 h to dissolve the lignin. The suspension was allowed to cool to room temperature and filtered through Whatman filter paper. The precipitate was added to 500 ml of 0.2 M NaOH and stirred for 8 h at room temperature to dissolve hemicellulose, and then filtered. The filtrate was heated at a temperature of 65°C, and 137 mL of 3% H2O2 was added in stages. Each addition of 1 mL 3% H2O2 to the filtrate was made and stirred constantly. Stirring was continued until a clear solution formed. 

The solution of 10% acetic acid in 95% ethanol with a ratio of 1 4 (v/v) was added to the sample solution and left at room temperature for 6 h until the precipitate formed. The suspension was centrifuged at 10,000 rpm for 15 min, the filtrate was discarded, and the precipitate was washed with 96% ethanol and dried in vacuum dryer. The washed precipitate was hemicellulose [33,34]. 

Bauer, W.D., Talmadge, K.W., Keegstra, K. Albersheim, P. (1973) The Structure of Plant Cell Walls II The Hemicellulose of the Walls of Suspension-cultured Sycamore Cells , Plant Physiology, 51, 174-87... 

Bauer W.D., Talmadge K.W., Keegstra K., Albersheim P, The structure of plant cell walls 11. The hemicellulose of the walls of suspension-cultured sycamore cells. Plant Physiol., 51(1), 1973, 174-187. 

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