Abstract
BackgroundThe bioconversion of lignocellulose to fermentable C5/C6-saccharides is composed of pretreatment and enzymatic hydrolysis. Lignin, as one of the main components, resists lignocellulose to be bio-digested. Alkali and organosolv treatments were reported to be able to delignify feedstocks and loose lignocellulose structure. In addition, the use of additives was an alternative way to block lignin and reduce the binding of cellulases to lignin during hydrolysis. However, the relatively high cost of these additives limits their commercial application.ResultsThis study explored the feasibility of using elephant grass (Pennisetum purpureum) and reed straw (Phragmites australis), both of which are important fibrous plants with high biomass, no-occupation of cultivated land, and soil phytoremediation, as feedstocks for bio-saccharification. Compared with typical agricultural residues, elephant grass and reed straw contained high contents of cellulose and hemicellulose. However, lignin droplets on the surface of elephant grass and the high lignin content in reed straw limited their hydrolysis performances. High hydrolysis yield was obtained for reed straw after organosolv and alkali pretreatments via increasing cellulose content and removing lignin. However, the hydrolysis of elephant grass was only enhanced by organosolv pretreatment. Further study showed that the addition of bovine serum albumin (BSA) or thioredoxin with His- and S-Tags (Trx-His-S) improved the hydrolysis of alkali-pretreated elephant grass. In particular, Trx-His-S was first used as an additive in lignocellulose saccharification. Its structural and catalytic properties were supposed to be beneficial for enzymatic hydrolysis.ConclusionsElephant grass and reed straw could be used as feedstocks for bioconversion. Organosolv and alkali pretreatments improved their enzymatic sugar production; however, the increase in hydrolysis yield of pretreated elephant grass was not as effective as that of reed straw. During the hydrolysis of alkali-pretreated elephant grass, Trx-His-S performed well as additive, and its structural and catalytic capability was beneficial for enzymatic hydrolysis.
Highlights
The bioconversion of lignocellulose to fermentable C5/C6-saccharides is composed of pretreatment and enzymatic hydrolysis
Sun et al suggested that the pretreatment with the diluted alkali could swell lignocellulosic materials, which led to a decrease in the degrees of polymerization and crystallinity [9]
Chemical compositions and bioconversion capability of reed straw and elephant grass Table 1 shows the chemical compositions of corn stover, wheat straw, reed straw, and elephant grass
Summary
The bioconversion of lignocellulose to fermentable C5/C6-saccharides is composed of pretreatment and enzymatic hydrolysis. As one of the main components, resists lignocellulose to be bio-digested. One of the main components in lignocellulose, cross-links with hemicellulose and cellulose, resulting in the resistance of lignocellulose to bio-digestion [5]. Many pretreatment methods have been developed with various solvents or catalysts, such as alkali, acid, organic solvents, and ionic liquid [4, 7] Among these methods, alkali pretreatment was able to exert strong delignification capability by breaking the cross-linkage between lignin and hemicellulose and by increasing the porosity of the substrate [8]. Organosolv pretreatment was reported as an alternative method to delignify and modify the structure of lignin, which could break the fibrous structure and reduce the degree of crystallinity [7]. Delignification and a loose structure were in favor to increase the access of cellulase to cellulose, which resulted in high sugar yield
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