Lignin–carbohydrate complexes: properties, applications, analyses, and methods of extraction: a review

Abstract

The complexity of lignin and hemicellulose segmentation has been known since the middle of the ninetieth century. Studies confirmed that all lignin units in coniferous species and 47–66% of lignin moieties in deciduous species are bound to hemicelluloses or cellulose molecules in lignin–carbohydrate complexes (LCC). Different types and proportions of lignin and polysaccharides present in biomass lead to the formation of LCC with a great variety of compositions and structures. The nature and amount of LCC linkages and lignin substructures affect the efficiency of pulping, hydrolysis, and digestibility of biomass. This review paper discusses the structures, compositions, and properties of LCC present in biomass and in the products obtained via pretreating biomass. Methods for extracting, fractionating, and analyzing LCC of biomass, pulp, and spent pulping liquors are critically reviewed. The main perspectives and challenges associated with these technologies are extensively discussed. LCC could be extracted from biomass following varied methods, among which dimethyl sulfoxide or dioxane (Björkman’s) and acetic acid (LCC-AcOH) processes are the most widely applied. The oxidation and methylation treatments of LCC materials elucidate the locations and frequency of binding sites of hemicelluloses to lignin. The two-dimensional nuclear magnetic resonance analysis allows the identification of the structure and the quantity of lignin–carbohydrate bonds involved in LCC. LCC application seems promising in medicine due to its high anti-HIV, anti-herpes, and anti-microbial activity. In addition, LCC was successfully employed as a precursor for the preparation of spherical biocarriers.

Potential of bagasse obtained using hydrothermal liquefaction pre‐treatment as a natural emulsifier

“…Szczerbowski et al (2014) reported lower values for unidentified cellulose derivative, anhydrohexose, at 1% after acid treatment of bagasse. In our study, the unidentified compounds at 49% of the bagasse extract may be attributed to water-soluble polysaccharides, lignin-carbohydrates complexes (Tarasov et al, 2018), acetyl groups derived from xylan (Carvalho et al, 2015) and organic acids. Lignin-carbohydrate complexes are molecules with hemicellulosic backbone covalently bonded to small lignin fragments from plant cell walls that are sometimes extracted during subcritical water conditions such as HTL (Mart ınez-Abad et al, 2018).…”

Even Visually Intact Cell Walls in Waterlogged Archaeological Wood Are Chemically Deteriorated and Mechanically Fragile: A Case of a 170 Year-Old Shipwreck

“…The loss of carboxyl group of glucuronic acid residues in hemicellulose probably indicates the partial loss of unconjugated ester linkages in lignin-carbohydrate complexes (LCCs) of VICWs in archaeological wood according to a previous report [14]. It is known that the covalent link between the carboxyl group of glucuronic acid residue in hemicelluloses and α-hydroxyl group of the lignin represents one kind of covalent links in LCCs [26,27]. In addition, the weak Py-GC/MS signal 2 (2-butenal), weak signal 3 (2-furan methanol) and weak signal 5 (2-hydroxy-3-methyl-2-cyclopenten-1-one) in the pyrogram of the WAW back up these findings [17,[28][29][30][31] (Figure 3B & Table S3).…”

Miscanthus x giganteus Stem versus Leaf-derived Lignins Differing in Monolignol Ratio and Linkage

“…Stem/leaf mixtures (Gig17M, Gig34M), stems (Gig17S, Gig34S) and leaves (Gig17L, Gig34L). However, HSQC NMR only considers signals for free C-H coupling (in case of further aromatic substituents, those fragments would not be recognized) [48,63,90]. So, further detailed analysis is required to explain deviations of the monolignol ratios obtained via pyrolysis GC/MS and HSQC-NMR.…”