Submitted to: Journal of Carbohydrate Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2005
Publication Date: 1/26/2006
Citation: Pu, Y., Ziemer, C.J., Ragauskas, A.J. 2006. Cross polarization/magic angle sample (CP/MAS) nuclear magnetic resonance (NMR) analysis of cellulase treated bleached softwood kraft pulp. Journal of Carbohydrate Chemistry. 341(5):591-597. Interpretive Summary: Cellulose is a carbohydrate that contributes to the structure of plants. Due to the types of chemical bonds that join the molecules of cellulose, it forms crystal-like structures which influences the access of enzymes to the chemical bonds of the cellulose. Access to the chemical bonds of cellulose by enzymes is important for the breakdown or digestion of the material. Nuclear magnetic resonance was used to examine the crystalline structure of cellulose (from bleached softwood pulp) before and during enzymatic hydrolysis by the enzyme 1,4-(1,3:1,4)-beta-D-glucan 4-glucano-hydrolase. Three types of crystalline structures were found in the cellulose (cellulose crystalline I alpha, cellulose crystalline I beta, and cellulose para-crystalline) as well as regions that were not crystallized. Each of these structures was hydrolyzed to a different extent by the enzyme used. Also observed was a rapid initial phase for hydrolysis of regions followed by a slow hydrolysis phase. Crystalline cellulose I alpha, para-crystalline and non-crystalline regions of cellulose were more susceptible to enzymatic hydrolysis than I beta during the initial phase. After the initial phase, all the regions are then similarly susceptible to enzymatic hydrolysis in the subsequent slow phase and hydrolyzed at the similar rate. The research results described in this report provide information on the microbial digestion of fiber which will assist nutritionists and microbiologists the ability to gain greater nutritional benefits from fiber included in diets.
Technical Abstract: Fully bleached softwood pulp cellulosic materials were hydrolyzed with cellulase (1,4-(1,3:1,4)-beta-D-glucan 4-glucano-hydrolase, EC 188.8.131.52) from Trichoderma reesei. Supermolecular structural features of cellulose during enzymatic hydrolysis were examined by using Cross Polarization/Magic Angle Sample - Nuclear Magnetic Resonance spectra in combination with line-fitting analysis. Cellulose crystalline I alpha allomorph in the pulp cellulosic material was more susceptible to enzymatic hydrolysis than I beta. Relative intensity of para-crystalline and amorphous regions exhibits a rapid decrease during the first eight hours of enzymatic hydrolysis and a subsequent slow phase. Cellulase hydrolysis of fully bleached softwood pulp is proposed to consist of two phases: initial rapid phase and subsequent slow phase. The I beta relative intensity and crystallinity are observed to increase in the initial phase, and then remain almost constant in the second phase. Crystalline cellulase I alpha, para-crystalline and amorphous regions of cellulose are more susceptible to cellulase hydrolysis than I beta during the initial phase. After the initial phase, all the domains of crystalline, para-crystalline and amorphous are then comparably susceptible to enzymatic hydrolysis in the subsequent slow phase and hydrolyzed at the similar rate.