Evaluation of nanoparticle‐immobilized cellulase for improved ethanol yield in simultaneous saccharification and fermentation reactions

Abstract

Ethanol yields were 2.1 (P = 0.06) to 2.3 (P = 0.01) times higher in simultaneous saccharification and fermentation (SSF) reactions of microcrystalline cellulose when cellulase was physisorbed on silica nanoparticles compared to enzyme in solution. In SSF reactions, cellulose is hydrolyzed to glucose by cellulase while yeast simultaneously ferments glucose to ethanol. The 35°C temperature and the presence of ethanol in SSF reactions are not optimal conditions for cellulase. Immobilization onto solid supports can stabilize the enzyme and promote activity at non-optimum reaction conditions. Mock SSF reactions that did not contain yeast were used to measure saccharification products and identify the mechanism for the improved ethanol yield using immobilized cellulase. Cellulase adsorbed to 40 nm silica nanoparticles produced 1.6 times (P = 0.01) more glucose than cellulase in solution in 96 h at pH 4.8 and 35°C. There was no significant accumulation (<250 µg) of soluble cellooligomers in either the solution or immobilized enzyme reactions. This suggests that the mechanism for the immobilized enzyme's improved glucose yield compared to solution enzyme is the increased conversion of insoluble cellulose hydrolysis products to soluble cellooligomers at 35°C and in the presence of ethanol. The results show that silica-immobilized cellulase can be used to produce increased ethanol yields in the conversion of lignocellulosic materials by SSF.

Kinetic Models and Effects of Mn(II) Ion on Ethanol Production from Cornstalks

“…Furthermore, the addition of Mn 2+ both initiated the anaerobic fermentation reaction at a lower temperature and decreased the cellulase dosage from 20 U/g to 10 U/g. Due to the reduced cellulose dosage and the reduced energy consumption allowed by the initiation of the anaerobic fermentation reaction at lower temperature (Yanase et al 2010;Lupoi and Smith 2011), ethanol production costs in the group with the addition of Mn 2+ were reduced. Table 3 shows that the hemicellulose content of cornstalks increased from 32.7% to 54.9%.…”

Production of Biofuels from Cellulose of Woody Biomass

“…Also, SHF has a faster hydrolysis rate than does SSF under optimized conditions [11,39]. In SSF process, cellulose is hydrolyzed to glucose by cellulase, while yeast spontaneously ferments glucose to ethanol [54]. The SSF usually has a higher productivity (ethanol produced per unit mass of dried feedstock per unit time, g/g.h) than does SHF, since SSF has a shorter operating time [39].…”

“…SSF). In one study, dissolved cellulase (500 µl, in 10 mM acetate buffer, pH 4.8 with 0.01 % (w/v) sodium azide) was immobilized on Aerosol OX-50 silica (40 nm average diameter particle, 1.4 m 2 surface area), and the SSF was carried out using this coated silica [54]. The results showed that the ethanol yields of the SSF process containing immobilized enzyme were 2.3 and 2.1 times higher than that of the SSF process containing enzyme in solutions at pH 4.8 and 5.3, respectively.…”

“…The results showed that the ethanol yields of the SSF process containing immobilized enzyme were 2.3 and 2.1 times higher than that of the SSF process containing enzyme in solutions at pH 4.8 and 5.3, respectively. The higher ethanol yield of the immobilized enzyme process was likely due to higher glucose yields as a result of increased enzymatic stability at the non-optimal enzyme conditions required for the SSF [54]. However, this process results in a higher ethanol yield under the optimum conditions of fermentation rather than that of enzyme hydrolysis.…”

“…However, this process results in a higher ethanol yield under the optimum conditions of fermentation rather than that of enzyme hydrolysis. This is because 1) the optimum conditions for the immobilized enzyme reaction may not coincide with those for the enzyme in solutions; 2) although the same mass of enzyme can be used in the solution and immobilized systems, it does not mean that the same amount of enzyme is available to participate in the hydrolysis reactions; and 3) enzyme immobilization results in a random orientation of adsorbed enzyme on the silica substrates, and this leads to some inactive enzyme due to buried or inaccessible active sites [54].…”