Selective precipitation and characterization of lignin-carbohydrate complexes (LCCs) from Eucalyptus.

MAIN CONCLUSION: Six types of lignin-carbohydrate complex (LCC) fractions were isolated from Eucalyptus. The acidic dioxane treatment applied significantly improved the yield of LCCs. The extraction conditions had a limited impact on the LCC structures and linkages. Characterization of the lignin-carbohydrate complex (LCC) structures and linkages promises to offer insight on plant cell wall chemistry. In this case, Eucalyptus LCCs were extracted by aqueous dioxane, and then precipitated sequentially by 70% ethanol, 100% ethanol, and acidic water (pH = 2). The composition and structure of the six LCC fractions obtained by selective precipitation were investigated by sugar analysis, molecular weight determination, and 2D HSQC NMR. It was found that the acidic (0.05-M HCl) dioxane treatment significantly improved the yield of LCCs (66.4% based on Klason lignin), which was higher than the neutral aqueous dioxane extraction, and the extraction condition showed limited impact on the LCC structures and linkages. In the fractionation process, the low-molecular-weight LCCs containing a high content of carbohydrates (60.3-63.2%) were first precipitated by 70% ethanol from the extractable solution. The phenyl glycoside (PhGlc) bonds (13.0-17.0 per 100Ar) and highly acetylated xylans were observed in the fractions recovered by the precipitation with 100% ethanol. On the other hand, such xylan-rich LCCs exhibited the highest frequency of ß-O-4 linkages. The benzyl ether (BE) bonds were only detected in the fractions obtained by acidic water precipitation.

Characterization of lignins isolated with alkali from the hydrothermal or dilute-acid pretreated rapeseed straw during bioethanol production.

A better understanding of the lignin in the straw of rapeseed, Brassica campestris L., is a prerequisite for promoting the biorefinery industry of rapeseed. Two different methods for fractionating lignin from rapeseed straw were proposed in this study. Lignin in the raw material was isolated with alkaline solution and recovered by acid precipitation. A comparison between two lignin preparations obtained from two different methods has been made in terms of yield and purity. The structural features were investigated by gel permeation chromatography, FT-IR spectroscopy, 2D-HSQC NMR and 31P NMR. Taking into consideration of the yield and purity, the proposed methods are effective for extracting lignin. NMR results showed that syringyl (S) was the predominant unit over guaiacyl (G) or p-hydroxyphenyl (H) units in the lignin preparations, and linkages ß-O-4', ß-ß' and ß-5' were also identified and quantified by NMR techniques. This study demonstrated that the combination of hydrothermal or dilute-acid pretreatment and alkaline process could efficiently isolate the lignins from the rapeseed straw to further applications for industries. It was found that the enzymatic hydrolysis of the two-step pretreated rapeseed straw increased 5.9 times than the straw without treatment, which is benefit for bioethanol production from rapeseed straw.

Fractionation of rapeseed straw by hydrothermal/dilute acid pretreatment combined with alkali post-treatment for improving its enzymatic hydrolysis.

The aim of the research was to evaluate the effect of combined treatments on fermentable sugar production from rapeseed straw. An optimum condition was found to be the combination of hydrothermal pretreatment at 180°C for 45min and post-treatment by 2% NaOH at 100°C for 2h, which was based on the quantity of monosaccharides released during enzymatic hydrolysis. As compared with the raw material without treatment, the combination of hydrothermal pretreatment and alkali post-treatment resulted in a significant increase of the saccharification rate by 5.9times. This process potentially turned rapeseed straw into value added products in accordance with the biorefinery concept.