Porosity and Its Effect on the Digestibility of Dilute Sulfuric Acid Pretreated Corn Stover

Abstract

Enzyme accessibility has been proposed as a limiting factor in the enzymatic conversion of the cellulose in biomass to glucose. Prior work has shown a strong correlation between porosity, measured as the change in the volume of pores accessible to a cellulase-sized molecule, and the initial digestibility of biomass pretreated by various methods. The goal of this work was to determine if porosity was one of the factors governing the overall enzymatic digestibility of the cellulose in dilute acid pretreated biomass. The porosity of wet pretreated corn stover was determined using the methods of solute exclusion and 1H nuclear magnetic resonance (NMR) thermoporometry. The solute exclusion method identified differences in the accessible pore volume of the pretreated samples compared to untreated corn stover; however, only very small differences in porosity were observed among samples pretreated with a range of severities, giving ethanol yields from 70 to 96%. No correlation was found between the volume accessible to an enzyme-sized molecule (diameter estimated to be 51 A) and the digestibility of the cellulose in dilute acid pretreated corn stover. 1H NMR thermoporometry was used to measure the amount of water in pores ranging from 20 to 200 A. As was the case for the solute exclusion method, a difference was observed in the pore volume of untreated and acid pretreated corn stover, but no significant differences in pore volume were measured for the different pretreated samples.

Cellulase digestibility of pretreated biomass is limited by cellulose accessibility

“…NMR measurements conducted on these samples showed that dilute acid pretreatment increased the porosity in corn stover (Ishizawa et al, 2007), suggesting that the observed increase in T. reesei Cel7A access to the cellulose in PCS is due to improved physical access within the biomass structure. However, no measurable differences in porosity were found between these PCS samples (Ishizawa et al, 2007). Sample porosity, therefore, cannot explain the observed differences in T. reesei Cel7A accessibility between differentially pretreated corn stover samples.…”

“…This concept has been discussed in the literature as relating changes in the porosity of the biomass sample to digestibility (Esteghlalian et al, 2001;Grethlein, 1985). NMR measurements conducted on these samples showed that dilute acid pretreatment increased the porosity in corn stover (Ishizawa et al, 2007), suggesting that the observed increase in T. reesei Cel7A access to the cellulose in PCS is due to improved physical access within the biomass structure. However, no measurable differences in porosity were found between these PCS samples (Ishizawa et al, 2007).…”

Experimental techniques for characterising water in wood covering the range from dry to fully water-saturated

“…The smallest solutes are saccharides such as glucose (0.8 nm) (Flournoy et al 1991;Kuga 1981;Lin et al 1987;Stone and Scallan 1968a;Wang et al 2011), mannitol (0.8 nm) (Carpita et al 1979), sucrose (1.0 nm) (Carpita et al 1979;Kuga 1981;Van Dyke 1972), cellobiose (1.0 nm) (Lin et al 1987), maltose (1.0 nm) (Flournoy et al 1991;Stone and Scallan 1968a), raffinose (1.2 nm) (Flournoy et al 1991;Kuga 1981;Stone and Scallan 1968a;Van Dyke 1972), and stachyose (1.4 nm) (Carpita et al 1979;Stone and Scallan 1968a). PEGs range in size from 0.44 nm for ethylene glycol (Kuga 1981) to 13.0 nm (Lin et al 1987;Van Dyke 1972), while dextrans have been reported in the literature from 1.8 nm in diameter (Ishizawa et al 2007) up to 586 nm (Arond and Frank 1954). Figure 5 shows how the solute diameter correlates with molecular mass for both PEGs and dextrans.…”

“…Fig. 5 a Diameter of dextran and PEG probe molecules as a function of molecular weight (based on data from Arond and Frank 1954;Carpita et al 1979;Day et al 1978;Flournoy et al 1991;Granath and Kvist 1967;Hill et al 2005;Ishizawa et al 2007;Kuga 1981;Lin et al 1987;Peters 1986;Stone et al 1969;Stone and Scallan 1968a;Van Dyke 1972;Wang et al 2011;Wong et al 1988). b Inaccessible cell wall water volume as a function of size of different molecular probes.…”

Efeito da lignina de bagaços de cana-de-açúcar pré-tratados na hidrólise enzimática da celulose

“…O pré-tratamento com ácido sulfúrico diluído tem sido amplamente utilizado, principalmente no processamento de gramíneas, com relativo sucesso (CANILHA et al, 2011;CASTRO;HSU et al, 2010;ISHIZAWA et al, 2007;SANTOS et al, 2011;WYMAN, 2004 essas gotículas são forçadas para fora da parede celular, alterando a sua distribuição topoquímica na biomassa pré-tratada (DONOHOE et al, 2008;CHENG, 2002). A figura 9 ilustra o comportamento da lignina nessas condições.…”