Changes in the structural properties and rate of hydrolysis of cotton fibers during extended enzymatic hydrolysis

Abstract

An extended enzymatic hydrolysis of cotton fibers by crude cellulase from Trichoderma pseudokoningii S-38 is described with characterization of both the enzyme changes of activities and cellulose structure. The hydrolysis rates declined drastically during the early stage and then slowly and steadily throughout the whole hydrolysis process the same trend could be seen during the following re-hydrolysis process. Morphological and structural changes to the fibers, such as swelling, frequent surface erosion, and variation in the packing and orientation of microfibrils, were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Observation of X-ray diffraction and IR spectra suggests that the hydrolysis process results in a gradual increase in the relative intensity of the hydrogen bond network, and a gradual decrease in the apparent crystal size of cellulose. The I(alpha) crystal phase was hydrolyzed more easily than was the I(beta) crystal phase. Apart from the inactivation of CBHs activity, changes in the packing and arrangement of microfibrils and the structural heterogeneity of cellulose during hydrolysis could be responsible for the reduction in the rate of reaction, especially in its later stages. The results indicate that the enzymatic hydrolysis of cellulose occurs on the outer layer of the fiber surface and that, following this, the process continues in a sub-layer manner.

Relationship between Crystallinity Index and Enzymatic Hydrolysis Performance of Celluloses Separated from Aquatic and Terrestrial Plant Materials

“…The crystallinity index (CrI) were determined based on the equation shown below (Kim and where I002 is the intensity of the diffraction from the 002 plane at 2θ=22.6° and Iam is the intensity of the background scatter measured at 2θ=18.7°. It is known that the I002 peak corresponds to the crystalline fraction and the Iam peak corresponds to the amorphous fraction (Wang et al 2006).…”

“…For example, during hydrolysis in hot-compressed water (HCW), the hydrolysis reactions of amorphous cellulose is considerably faster than for crystalline cellulose (Yu and Wu 2011;Yu and Wu 2010). For enzymatic hydrolysis of microcrystalline cellulose, it has also been reported that the lower cellulose CrI, the higher will be the sugar yield and the faster will be the hydrolysis reaction rate (Fan et al 1981;Peng et al 2013;Wang et al 2006). However, besides the intrinsic crystalline structure of microcrystalline cellulose, the availability of enzymes is also an important factor that determines the reaction rate of enzymatic hydrolysis of microcrystalline cellulose.…”

Evolution and impact of cellulose architecture during enzymatic hydrolysis by fungal cellulases

“…The role of crystallinity during enzymatic hydrolysis is still controversial and may not directly explain the slowdown of the reaction. Chen et al [33] and Wang et al [35] found only a slight increase of conversion whereas some authors did not find any increase of the crystallinity index [14,36]. Other techniques were recently used to characterize nanometer changes in cellulose structure such as smallangle X-ray scattering (SAXS) [36] or small-angle neutron scattering (SANS) [37] which are suitable for the interface characterization.…”

“…Evolution of the cellulose surface morphology was recently investigated by SANS [38] which has the advantage to be a non-destructive and more penetrating technique than SAXS. This was also investigated by scanning electron microscopy (SEM) and results showed a clear decrease in the length of cotton linters and a non-uniformity of particle size after several hours of enzymatic hydrolysis [29,35]. Using Fiber Quality Analyser Park et al [39] showed a clear decrease in particle size and other authors [3,37] correlated the particles size decrease to the increase in surface area.…”

“…Restarting hydrolysis with fresh enzyme is an adequate experiment to measure the losses of substrate reactivity [35,[40][41][42]. It is still difficult to explain the decrease of the reaction rate vis a vis the evolution of morphological features of the substrate.…”