Hemicellulase hydrolysis

Hemicellulase Hydrolysis of (3-1,4-glucans, oi-L-arabino-sides, (3-D-mannosides, l,3-(3-D-xylans, and other polysaccharides, yielding polysaccharides of lower molecular weight. 

The cambium was isolated firom spruce (Picea abies) logs felled in October-November. The bark was stripped off, and the cambium was removed by gentle scraping. The isolated cambium was immediately fiozen in liquid nitrogen and fi-eeze-dried. The carbohydrate composition of the isolated cambium was analysed by HPLC after enzymatic hydrolysis using Pectinex Ultra and a mixture of cellulases and hemicellulases (Buchert et al 1993). 

Water removal on the paper machine has been shown to improve as a result of limited hydrolysis of the fibres in recycled paper. Mixtures of cellulases and hemicellulases were found to decrease the SR-value, which describes the drainage behaviour of the fibres (45), The effect is apparently due to fibrillation or change in the composition of fine particles. 

The combined action of xylanase and mannanase on sprucewood holocellulose increased the hydrolysis of hemicelluloses without any detectable attack of cellulose. At the end of the experiments—i.e., after 48 hr of xylanase incubation followed by 32 hr of combined xylanase-mannanase incubation—about half the hemicelluloses present in the starting material were selectively converted into low-molecular-weight sugars. The amount of mannan removed was two times higher than after 80 hr of incubation with mannanase only. Unexpectedly, the xylan dissolution was scarcely increased by the combined action of the two hemicellulases. 

In contrast to cellulose, which is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength. It is easily hydrolyzed by dilute acid or base, but nature provides an arsenal of hemicellulase enzymes for its hydrolysis. Hemicellulases are commercially important because they open the structure of wood for easier bleaching and thus support the introduction of ECF or TCF methods. Many different pentoses are usually present in hemicellulose. Xylose, however, is always the predominating sugar. The pentoses are also present in rings (not shown) that can be five- or six-membered. 

The complex nature and interconnectivity of plant cell wall polymers preclude straightforward enzymatic digestion. There are dozens of enzyme families involved in plant cell wall hydrolysis, including cellulases, hemicellu-lases, pectinases, and lignin-modifying enzymes. The Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (IUBMB) has classified cellulases and hemicellulases, like all enzymes, into different classes based on activity. Table 33.2 and Table 33.3, compiled from the IUBMB enzyme nomenclature database (http //www.chem.qmul.ac.uk/iubmb/ enzyme/), list the IUBMB enzyme classifications for cellulases and hemicellulases.153... 

Application and Principle This procedure is used to determine hemicellulase activity of preparations derived from A.J-pergillus niger var. The test is based on the enzymatic hydrolysis of the interior glucosidic bonds of a defined locust (carob) bean gum substrate at 40° and pH 4.5. Determine the corresponding reduction in substrate viscosity with a calibrated viscometer. 

Biochemical conversion processes Enz)unes and micro-organisms are frequently used as biocatalysts to convert biomass or biomass-derived compounds into desirable products. Cellulase and hemicellulase enzymes break down the carbohydrate fractions of biomass into five-and six-carbon sugars, a process known as hydrolysis. Yeast and bacteria ferment the sugars into products such as ethanol. Biotechnology advances are expected to lead to dramatic biochemical conversion improvements. 

Few, if any, simple glycosidases have been crystallized, and, indeed, for many hydrolyses, extremely complex mixtures of enzymes, for example, almond emulsin, are often used. The specificity of such complex mixtures may be increased not only by fractionation, but by the addition of appropriate inhibitors. Thus, commercial hemicellulase normally hydrolyzes both the L-arabinose-D-xylose and the n-xylose-n-xylose link in arabi-noxylans. Addition of L-arabinono-1,4-lactone to the enzyme digest, however, inhibits hydrolysis of the former links (see Conchie and Levvy ) and... 

Hydrolysis of Ammonia-pretreated Sugar Cane Bagasse with Cellulase, P-Glucosidase, and Hemicellulase Preparations... 

Keywords Ammonia pretreatment Sugar cane bagasse Hydrolysis Cellulase Hemicellulase... 

Analysis of carbohydrates in delignified wood and pulp involved enzymic hydrolysis (cellulase, hemicellulase), derivatization of the free sugars with ethyl p-aminobenzoate and capillary zone electrophoresis. All reducing sugars, i.e. neutral monosaccharides as well as uronic acids, were quantified in a single analytical run, and 4-deoxy-P-L-r/ireo-hex-4-enopyranosyluronic acid present in the pulps was also detected. ... 

This chapter focuses on production of sugars from cellulosic or fibrous biomass feedstocks using conversion routes based on enzymatic hydrolysis. Section 4.2 describes the nature of cellulase and hemicellulase enzyme systems capable of depolymerizing cellulose and hemicellulose to soluble sugars, and reviews the prominent concepts of enzyme synergy and biomass recalcitrance. Performance of enzymatic hydrolysis under anticipated real-world processing conditions involving... 

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