Analysis of celluloses, plant holocelluloses, and wood pulps by size-exclusion chromatography/multi-angle laser-light scattering

Size-exclusion chromatography with multi-angle laser-light scattering and refractive index detection (SEC/MALLS/RI) provides the number- and weight-average molar masses, molar mass distributions, conformations, and linear/branched structures of polymers. In the case of pure celluloses including highly crystalline tunicate and alga celluloses, and hemicellulose-rich plant holocelluloses, soaking in ethylene diamine (EDA) and subsequent solvent exchange to N,N-dimethylacetamide (DMAc) though methanol is effective for complete dissolution in ∼8% (w/w) LiCl/DMAc. SEC/MALLS/RI analysis can, therefore, be applied to pure celluloses, chemical wood pulps, and plant holocelluloses after dissolution in ∼8% (w/w) LiCl/DMAc, dilution to 1% (w/v) LiCl/DMAc and membrane filtration. All pure celluloses and the high-molar-mass cellulose fractions of hardwood and grass holocelluloses have linear and random-coil conformations and various average molar masses and molar mass distributions depending on the cellulose and holocellulose resources. In contrast, Japanese cedar (i.e., softwood) holocellulose and softwood bleached kraft pulp have alkali-stable cellulose/glucomannan branched structures in the high-molar-mass fractions.

Enhanced enzymatic hydrolysis of corncob by ultrasound-assisted soaking in aqueous ammonia pretreatment

Ultrasound-assisted soaking in aqueous ammonia (USAA) pretreatment with 15 wt% aqueous ammonia under low temperature (~ 60 °C) and short-time (< 12 min) low-frequency (20 kHz, 60-650 W) ultrasound has been investigated for enhancement of enzymatic hydrolysis of corncob. Operational parameters of energy density (2.93-17.07 W/mL) and sonication time (0.34-11.66 min) that affect cellulose recovery, delignification, and sugar recovery yield were studied and optimized. The maximum cellulose recovery, delignification and sugar recovery yield determined at the optimum conditions (energy density 10 W/mL, sonication time 11.66 min) were 83.8, 84.7, and 77.6%, respectively. The corncob pretreated using USAA has a lower hemicellulose content (28.9% vs 31.8%), a slightly lower crystallinity index value (42.7% vs 43.7%), and a larger surface cavity diameter (> 36 μm vs < 20 μm) than that pretreated using soaking in aqueous ammonia (SAA) pretreatment. The USAA pretreatment was proved to be a reliable and effective method for corncob pretreatment.

Non-ionic surfactants do not consistently improve the enzymatic hydrolysis of pure cellulose

Non-ionic surfactants have been frequently reported to improve the enzymatic hydrolysis of pretreated lignocellulosic biomass and pure cellulose. However, how the hydrolysis condition, substrate structure and cellulase formulation affect the beneficial action of surfactants has not been well elucidated. In this work, it was found that the enzymatic hydrolysis of pure cellulose was not consistently improved by surfactants. Contrarily, high surfactant concentration, e.g. 5 g/L, which greatly improved the hydrolysis of dilute acid pretreated substrates, actually showed notable inhibition to pure cellulose conversion in the late phase of hydrolysis. Under an optimal hydrolysis condition, the improvement by surfactant was limited, but under harsh conditions surfactant indeed could enhance cellulose conversion. It was proposed that non-ionic surfactants could interact with substrates and cellulases to impact the adsorption behaviors of cellulases. Therefore, the beneficial action of surfactants on pure cellulose hydrolysis is influenced by hydrolysis condition, cellulose structural features and cellulase formulation.

The use of carbohydrate binding modules (CBMs) to monitor changes in fragmentation and cellulose fiber surface morphology during cellulase- and Swollenin-induced deconstruction of lignocellulosic substrates

Although the actions of many of the hydrolytic enzymes involved in cellulose hydrolysis are relatively well understood, the contributions that amorphogenesis-inducing proteins might contribute to cellulose deconstruction are still relatively undefined. Earlier work has shown that disruptive proteins, such as the non-hydrolytic non-oxidative protein Swollenin, can open up and disaggregate the less-ordered regions of lignocellulosic substrates. Within the cellulosic fraction, relatively disordered, amorphous regions known as dislocations are known to occur along the length of the fibers. It was postulated that Swollenin might act synergistically with hydrolytic enzymes to initiate biomass deconstruction within these dislocation regions. Carbohydrate binding modules (CBMs) that preferentially bind to cellulosic substructures were fluorescently labeled. They were imaged, using confocal microscopy, to assess the distribution of crystalline and amorphous cellulose at the fiber surface, as well as to track changes in surface morphology over the course of enzymatic hydrolysis and fiber fragmentation. Swollenin was shown to promote targeted disruption of the cellulosic structure at fiber dislocations.