Multi-scale structural and chemical analysis of sugarcane bagasse in the process of sequential acid–base pretreatment and ethanol production by Scheffersomyces shehatae and Saccharomyces cerevisiae

Abstract

BackgroundHeavy usage of gasoline, burgeoning fuel prices, and environmental issues have paved the way for the exploration of cellulosic ethanol. Cellulosic ethanol production technologies are emerging and require continued technological advancements. One of the most challenging issues is the pretreatment of lignocellulosic biomass for the desired sugars yields after enzymatic hydrolysis. We hypothesized that consecutive dilute sulfuric acid-dilute sodium hydroxide pretreatment would overcome the native recalcitrance of sugarcane bagasse (SB) by enhancing cellulase accessibility of the embedded cellulosic microfibrils.ResultsSB hemicellulosic hydrolysate after concentration by vacuum evaporation and detoxification showed 30.89 g/l xylose along with other products (0.32 g/l glucose, 2.31 g/l arabinose, and 1.26 g/l acetic acid). The recovered cellulignin was subsequently delignified by sodium hydroxide mediated pretreatment. The acid–base pretreated material released 48.50 g/l total reducing sugars (0.91 g sugars/g cellulose amount in SB) after enzymatic hydrolysis. Ultra-structural mapping of acid–base pretreated and enzyme hydrolyzed SB by microscopic analysis (scanning electron microcopy (SEM), transmitted light microscopy (TLM), and spectroscopic analysis (X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Fourier transform near-infrared (FT-NIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy) elucidated the molecular changes in hemicellulose, cellulose, and lignin components of bagasse. The detoxified hemicellulosic hydrolysate was fermented by Scheffersomyces shehatae (syn. Candida shehatae UFMG HM 52.2) and resulted in 9.11 g/l ethanol production (yield 0.38 g/g) after 48 hours of fermentation. Enzymatic hydrolysate when fermented by Saccharomyces cerevisiae 174 revealed 8.13 g/l ethanol (yield 0.22 g/g) after 72 hours of fermentation.ConclusionsMulti-scale structural studies of SB after sequential acid–base pretreatment and enzymatic hydrolysis showed marked changes in hemicellulose and lignin removal at molecular level. The cellulosic material showed high saccharification efficiency after enzymatic hydrolysis. Hemicellulosic and cellulosic hydrolysates revealed moderate ethanol production by S. shehatae and S. cerevisiae under batch fermentation conditions.

Multi-Scale Structural Studies of Sequential Ionic Liquids and Alkali Pretreated Corn Stover and Sugarcane Bagasse

“…The two peaks of CH2 symmetric and CH asymmetric stretching respectively were present at 2850 cm −1 and 2918 cm −1 being characteristic of cellulose [25]. The slight disturbances in the CS-EtIm [Ac]+Na and CS-BmIm [Ac]+Na peak at 2850 cm −1 indicated that after these pretreatments, the cellulose chain had been affected [26]. In short, the presence of lignocellulosic matrix was confirmed by these bands.…”

Enzymatic Saccharification of Acid/Alkali Pre-treated, Mill-run, and Depithed Sugarcane Bagasse

“…When comparing these values with the literature values (Rainey 2009;da Silva et al 2010;Rocha et al 2011;Rabelo et al 2011;Canilha et al 2012 andChandel et al 2014), it can be observed that there is not much difference. The pre-treatment of substrate with 3% H2SO4 decreased the proportion of hemicellulose and lignin and increased the cellulose content for both depithed and mill-run bagasse, which was predictable since the acid pretreatment was used to remove hemicellulose.…”

“…The region between 1,200 and 1,100 cm -1 is a large contribution of hemicellulose and cellulose, which exhibits a maximum value around 1,035 cm -1 due to C-O stretching and 1,164 cm -1 for the asymmetrical stretching of C-O-C (Pandey 1999;Colom et al 2003;Pandey 2005;Chandel et al 2014). The region around 1,247 cm -1 was due to the stretching of C-O, which is characteristic of hemicellulose and lignin (Pandey and Pitman 2003;Chandel et al 2014). A band around 1,458 cm -1 is reported to be a deformation of lignin CH2 and CH3, and 1,604 cm -1 is reported to be stretching of the C=C and C=O lignin aromatic ring.…”

“…The band at 898 cm -1 is characteristic of the glycosidic bond β-(1 → 4) cellulose, corresponding to the C-H deformation in cellulose (Pandey and Pitman 2003;Oh et al 2005;Chandel et al 2014). The region between 1,200 and 1,100 cm -1 is a large contribution of hemicellulose and cellulose, which exhibits a maximum value around 1,035 cm -1 due to C-O stretching and 1,164 cm -1 for the asymmetrical stretching of C-O-C (Pandey 1999;Colom et al 2003;Pandey 2005;Chandel et al 2014). The region around 1,247 cm -1 was due to the stretching of C-O, which is characteristic of hemicellulose and lignin (Pandey and Pitman 2003;Chandel et al 2014).…”

Construction of recombinant Yarrowia lipolytica and its application in bio-transformation of lignocellulose

“…It is a good way to solve the problem of wasted cellulose resources and a lack of energy. [7][8][9] Lignocellulose widely exists in grains, beans, maize, rice, and some subsidiary agricultural products. Using lignocellulose in the feed industry is another important application.…”