Bisulfite pretreatment changes the structure and properties of oil palm empty fruit bunch to improve enzymatic hydrolysis and bioethanol production

Abstract

Bisulfite pretreatment is a proven effective method for improving the enzymatic hydrolysis of empty fruit bunch (EFB) from oil palm for bioethanol production. In this study, we set out to determine the changes that occur in the structure and properties of EFB materials and fractions of hemicellulose and lignin during the bisulfite pretreatment process. The results showed that the crystallinity of cellulose in EFB increased after bisulfite pretreatment, whereas the EFB surface was damaged to various degrees. The orderly structure of EFB, which was maintained by hydrogen bonds, was destroyed by bisulfite pretreatment. Bisulfite pretreatment also hydrolyzed the glycosidic bonds of the xylan backbone of hemicellulose, thereby decreasing the molecular weight and shortening the xylan chains. The lignin fractions obtained from EFB and pretreated EFB were typically G-S lignin, and with low content of H units. Meanwhile, de-etherification occurred at the β-O-4 linkage, which was accompanied by polymerization and demethoxylation as a result of bisulfite pretreatment. The adsorption ability of cellulase differed for the various lignin fractions, and the water-soluble lignin fractions had higher adsorption capacity on cellulase than the milled wood lignin. In general, the changes in the structure and properties of EFB provided insight into the benefits of bisulfite pretreatment.

Characteristics of Lignin Fractions from Dilute Acid Pretreated Switchgrass and Their Effect on Cellobiohydrolase from Trichoderma longibrachiatum

“…For the S/G ratio, we also observed positive correlations with maximum adsorption capacity (y = 3.1233x + 3.7043, R 2 = 0.99), Kads (y = 0.6931x + 2.9581, R 2 = 0.97), and binding strength (y = 19.234x + 4.6808, R 2 = 0.99). Similarly, Tan and coworkers (Tan et al, 2015) observed that the milled wood lignin from bisulfite pretreated oil palm empty fruit bunch with a higher S/G ratio showed higher enzyme adsorption. In addition, negative correlations of guaiacyl OH content with maximum adsorption capacity (y = −21.135x + 29.475, R 2 = 0.98), Kads (y = −4.6209x + 8.7006, R 2 = 0.91) and binding strength (y = −131.61x + 167.39, R 2 = 0.99) were found.…”

“…In addition, negative correlations of guaiacyl OH content with maximum adsorption capacity (y = −21.135x + 29.475, R 2 = 0.98), Kads (y = −4.6209x + 8.7006, R 2 = 0.91) and binding strength (y = −131.61x + 167.39, R 2 = 0.99) were found. The effect of molecular weights and uniformity in lignin fragment size on the cellulase binding has been studied before (Guo et al, 2014;Tan et al, 2015). Among the three lignin fractions from dilute acid pretreated switchgrass, lignin with higher PDI absorbed less CBH during the binding process.…”

Hydrolysate-Recycled Liquid Hot Water Pretreatment of Reed Straw and Corn Stover for Bioethanol Production with Fed-Batch, Semi-Simultaneous Saccharification and Fermentation

“…Lignin is an amorphous heteropolymer consisting of three different phenylpropane units: guiacyl, syringyl, and p-hydroxyphenyl (Tan et al 2015). Because of its structure, lignin is generally a critical resistance factor against the enzymatic hydrolysis of cellulose (Alvira et al 2010).…”

Structural Characterization and Effect on Enzymatic Hydrolysis of Milled Wood Lignin Isolated from Reed Straw and Corn Stover Pretreated with Liquid Hot Water

“…Bioethanol obtained from lignocellulosic biomass is considered to be a potential alternative energy source that could reduce the current reliance on fossil fuels (Romaní et al 2012;Tan et al 2015). A typical process for converting lignocellulosic biomass into bioethanol generally involves three steps: pretreatment, enzymatic hydrolysis, and fermentation.…”

“…A typical process for converting lignocellulosic biomass into bioethanol generally involves three steps: pretreatment, enzymatic hydrolysis, and fermentation. The key step that enables bioconversion of the lignocellulosic biomass is enzymatic hydrolysis, which efficiently converts cellulose into fermentable sugars (Mood et al 2013;Tan et al 2015). The efficiency of the enzymatic hydrolysis of untreated lignocellulosic biomass is low because of its firm structure, and thus, the industrialization of bioethanol from lignocellulosic biomass remains restricted.…”