Bacillus megaterium P1, a bacterial strain capable of hydrolyzing chitosan, was isolated from soil samples. Chitosan-degrading activity was induced by chitosan but not by its constituent D-glucosamine. Extracellular secretion of chitosanase reached levels corresponding to 1 U/mI under optimal conditions. Three chitosandegrading proteins (chitosanases A, B, and C) were purified to homogeneity. Chitosanase A (43 kilodaltons) was highly specific for chitosan and represented the major chitosan-hydrolyzing species. Chitosanases B (39.5 kilodaltons) and C (22 kilodaltons) corresponded to minor activities and possessed comparable specific activities toward chitosan, chitin, and cellulose. Chitosanase A was active from pH 4.5 to 6.5 and was stable on the basis of activity up to 45°C. The optimum temperature for enzymatic chitosan hydrolysis was 50°C. Kinetic studies on chitosanase A suggest that the enzyme is substrate inhibited. The apparent Km and Vmax determined at 22°C and pH 5.6 were 0.8 mg/ml and 280 U/mg, respectively. End products of chitosan hydrolysis by each of the three chitosanases were identified as glucosamine oligomers, similar to those obtained for previously reported chitosanase digestions.
Chitosan, the deacetylated derivative of chitin, was until recently produced by hydrolysis in 50% (w/v) NaOH. Application of thermo-mechano-chemical technology to chitin deacetylation was evaluated as an alternative method of chitosan production. This process consists of a cascade reactor unit operating under reduced alkaline conditions of 10% (w/v) NaOH. Prior mercerization of chitin at 4 degrees C for 24 h was required for high deacetylation yields. Sudden decompression of the aqueous alkaline suspension of mercerized chitin resulted in near complete deacetylation of chitin. Reactor residence time was 90 s at 230 degrees C prior to decompression. The chitosan produced was characterized by elemental analysis, (13)C-NMR and enzymatic depolymerization. Enzymatic determination of the degree of acetylation of chitin/chitosan mixtures was also investigated. Relative chitinase and/or chitosanase digestibilities were shown to be strongly dependent on chitin deacetylation. Based on enzymatic digestibilities, the alkaline aqueous high shear process does not appear to produce significant secondary products. Correlation of chitosanase digestibility with percentage of deacetylation provides a simple biological assay to study chitosan composition.
Black spruce (Picea mariana) wood chips were subjected to enzymatic pretreatments, using an enzyme formulation containing cellulolytic and hemicellulolytic enzymes, combined with light mechanical treatments including downsizing and/or compression/decompression. These pretreatments were followed by 3 stages of mechanical refining in a labscale disc refiner. Depending on the treatment, the overall energy savings obtained could be as high as 15%. Most of the savings were obtained during the first stage of refining. Pulps collected after this stage were imaged using TEM and SEM. Differences were observed between differing treatment types. The most significant differences were seen when macerated chips were compressed and allowed to decompress in enzyme solutions. Enzyme treatments are able to change the rupture pattern during refining, thus lowering the overall specific energy consumption (SEC) as evidenced by improved pulp freeness and direct energy measurements. Increasing enzyme penetration helps to improve the overall SEC savings and also improves the distribution of energy savings throughout the refining stages by moving initial fiber separation from the middle lamella into the secondary wall.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.