The hemicelluloses of bracken Part II. A galactoglucomannan

A galactoglucomannan has been isolated from the stem tissues of a fern, bracken (Pteridium aquilinum). It had [] −35° and, on hydrolysis, yielded mannose, glucose, and galactose in the molar ratios of 60:15:1. Mild hydrolysis with acid released galactose only. The d.p., determined by periodate-oxidation and Smith-degradation studies, was 43–45 for a doubly branched molecule. The methylated galactoglucomannan had a d.p. of 25–30 by ebulliometry. Methylation analysis, in combination with other evidence, indicated that the hemicellulose had β-(1→4)-linked -glucopyranose and -mannopyranose residues in the ratio of 1 to 4, with residues of the latter contiguous. -Mannopyranosidic and -galactopyranosidic residues were present as non-reducing end-groups in the ratio of 7 to 1, but there was no evidence of non-reducing -glucopyranosidic residues. The branching was to 6-positions on the main glucomannan chain and was probably -(1→6). The galactoglucomannan is similar to hemicelluloses isolated from softwoods, but the former has a lower d.p.     

The hydrolysis of bagasse hemicelluloses by selected strains of Cellulomonas

Summary The enhanced cellulolytic activity of a Cellulomonas mutant has been shown to apply also to its ability to hydrolyse xylan-containing hemicelluloses. The hydrolytic activity was directly proportional to the xylose content in the hemicellulose substrate.     

Fractional purification and bioconversion of hemicelluloses

Hemicelluloses are types of plant cell wall polysaccharides, and the world's second most abundant renewable polymers after cellulose in lignocellulosic materials. They represent a type of hetero-polysaccharide with complex structure containing glucose, xylose, mannose, galactose, arabinose, rhamnose, glucuronic acid, and galacturonic acid in various amounts, depending on the source. Hemicelluloses are usually bonded to other cell-wall components such as cellulose, cell-wall proteins, lignin, and phenolic compounds by covalent and hydrogen bonds, and by ionic and hydrophobic interactions. This paper provides a review on hemicelluloses from lignocellulosic materials, especially in regard to their isolation and purification methods, and bioconversion. Current isolation and purification strategies are summarized, including: alkali peroxide extraction, organic solvent extraction, steam explosion, ultrasound-assisted extraction, microwave-assisted extraction, column chromatography, and membrane separation. In addition, the bioconversion of hemicelluloses including pretreatment, enzymatic hydrolysis, and fermentation are discussed.     

Bioconversion of hemicelluloses into fungal protein

Summary The utilization of cellulose from one ton of lignocellulose for ethanol production would yield 150–250 kg of hemicelluloses. The total soluble solids in the hemicellulose fraction (HF) obtained with the Université de Sherbrooke (UdeS) process contained about 56% carbohydrates. These carbohydrates were present in the form of oligomers of various sugars, predominantly xylose. All the test fungi,Chaetomium cellulolyticum, C. cellulolyticum (asporogenous mutant) andPleurotus sajor-caju, were capable of utilizing all the carbohydrates present in HF.C. cellulolyticum gave the highest amount of protein (7 g/l) from 19 g carbohydrates/l. The yield of protein was higher than expected, indicating that carbon compounds other than reducing sugars present in HF might have been consumed for fungal growth. The inhibitory effect of toxic compounds on protein production increased with an increase in concentration of soluble solids in HF. The inhibitory effect was overcome by increasing the pH of the medium to 6.0 or 7.0. Fungal protein production from hemicelluloses will give extra revenue in our integrated approach for ethanol production from lignocelluloses.NRCC publication No. 26277.     

Cellulose and hemicelluloses recovery from grape stalks

In this work, two mild chemical fractionation procedures were compared to separate and recover lignocellulosic components from grape stalks. The first method consisted of mild acid hydrolysis for hemicelluloses separation, followed by an alkaline/oxidative step for lignin solubilization, while in the second method the acid hydrolysis was preceded by an alkali steeping phase. Influence of the length of the first step of both methods (from 2 to 24 h) on monosaccharides and cellulose yields was investigated. The first method allowed a higher sugar recovery for longer times, and a slightly lower amount of cellulose. Cellulose residues from both the methods were comparable for cellulose content and thermal profile (studied by differential scanning calorimetry). Acid hydrolysis of the first step was carried out also in autoclave, showing that xylan degradation could be described by a first order kinetics where at higher temperature the presence of a fast reaction and a slow reacting fraction must be accounted for.     

Oak wood hemicelluloses extracted with aqueous-alcoholic media

Hemicellulose fractions were isolated from oak wood ethanol extracts (40–90%). To determine the composition of these fractions, they were hydrolyzed and the hydrolysis products in the form of trimethylsilyl derivatives were analyzed by GLC/MS. Depending on the content of the ethanol, hemicelluloses of a different composition were extracted from wood. In alcohols that were kept in oak wood, intended for manufacturing brandy and whisky, the content of the hemicelluloses increased depending on the duration of storage. It is assumed that this makes drinks more full-bodied and makes them softer.     

Extraction of water-soluble hemicelluloses from barley husks

Heat treatment of barley husks was performed to extract arabinoxylan with high yield and high weight-averaged molecular mass (M(W)). Microwave irradiation was employed for initial screening of suitable residence times (2-15 min), temperatures (120-210 degrees C) and initial pH (3-13) of the reaction slurry. Microwave irradiation was shown to be a good method for predicting the effects of heat treatment on a larger scale using steam pretreatment. A M(W) of about 40,000 Da was achieved without the addition of chemicals, by both microwave irradiation and steam pretreatment, with a yield of about 9%. The yield was significantly increased by slightly increasing the severity factor. However, the M(W) decreased below 20,000 Da at severity factors above 3.7. Arabinosyl side groups were enzymatically hydrolysed from the arabinoxylan by alpha-L-arabinofuranosidase to a degree of 47%, demonstrating the ability to specifically alter the side group substitution of arabinoxylans with the use of enzymes.     

The effect of hemicelluloses on wood pulp nanofibrillation and nanofiber network characteristics

Hemicelluloses as matrix substances showed an important role in nanofibrillation of wood pulp. Never-dried and once-dried pulps with different amounts of hemicelluloses were fibrillated using a grinding treatment. The degree of fibrillation was evaluated by scanning electron microscopy observation of the fibrillated pulps and light transmittance measurements of the fibrillated pulp/acrylic resin composites. With a one-pass grinding treatment, the once-dried pulp with higher hemicellulose content was fibrillated into 10-20 nm wide fibers as easily as the never-dried pulps, while the once-dried pulp with lower hemicellulose content was not fibrillated into uniform nanosized fibers. This result indicates that hemicelluloses act as inhibitors of the coalescence of microfibrils during drying and facilitate the nanofibrillation of once-dried pulp. Furthermore, hemicelluloses provide adhesion between nanofibers, contributing to reduction of thermal expansion and enhancement of mechanical properties in the composites.     

Growth ofAureobasidium pullulans on waste water hemicelluloses

Strain Aureobasidium pullulans capable of utilizing hemicelluloses and xylan was cultivated on processed waste dialysis liquor from the production of viscose fibres, containing about 1.5% hemocelluloses. Basic conditions of biomass production were tested on a laboratory scale. The dialysis waste liquor adjusted with mineral acids to pH 4--5 and supplemented with 0.05% yeast autolyzate and 0.2% ammonium sulphate affords protein yields of about 0.8 g/l, corresponding to 4.0--4.5 g dry biomass. Biomass is isolated together with residual water-insoluble hemicelluloses which are not utilized by the microorganism. The total utilization of hemicelluloses attains about 70%.     

DMSO-soluble hemicelluloses from the husk of Sorghum grain

The chlorite holotellulose from the grain husk of Sorghum bicolor was extracted with DMSO and the hemicellulosic material separated into water-solu