Comparison of the Structural Characteristics of Cellulolytic Enzyme Lignin Preparations Isolated from Wheat Straw Stem and Leaf

Abstract

Lignin structure has been considered to be an important factor that significantly influences the biorefinery processes. In this work, the effect of ball milling on the structural components and extractable lignin in enzymatic residues was evaluated, and the structural characteristics of the cellulolytic enzyme lignin preparations isolated from wheat straw stem (SCEL) and leaf (LCEL) were comparatively investigated by a combination of nitrobenzene oxidation (NBO), ozonation, infrared spectroscopy, and 1 H− 13 C heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR). The results showed that 4 h ball-milled samples were good enough for structural analysis with high lignin yield. Both CELs are typical p-hydroxyphenylguaiacyl-syringyl lignins which are associated with pcoumarates and ferulates. However, the structure of lignin in wheat straw stem is rather different from that in leaf. Compared to stem lignin, leaf lignin has lower product yields of NBO and ozonation, lower erythro/threo ratio, and higher condensation degree. The analysis of 2D HSQC NMR indicated that the S/G ratio of SCEL was 0.8, which is about twice as much as that of LCEL. The flavone tricin is incorporated into both stem and leaf lignins. The content of tricin in LCEL is higher than that in SCEL.

The impact of lignin downregulation on alfalfa yield, chemical composition, and in vitro gas production

“…Leaf tissue also had a lower absorbance ratio between 1515 and 1603 cm −1 , which the authors proposed was indicative of less condensed and less cross‐linked lignin structures. Others also reported a higher S/G ratio in the leaf tissue than in stem tissue of wheat straw. These authors also noted that the structure of lignin differed for leaf and stem tissues.…”

“…Lignin structure also likely contributes to this variability. Lignin structure was not uniform and differed for lignin found in leaf versus stem tissue of wheat straw . When lignin synthesis was reduced, plants responded by changing the nature and deposition patterns such that structural, antifungal, and water transport functions were affected less than proportionally to the lignin deficit .…”

High-purity lignin isolated from poplar wood meal through dissolving treatment with deep eutectic solvents

“…Compared with the NBO products of poplar wood meal and DES-L, the NBO products yields of DES-L have a significant reduction, which is attributed to the cleavage of a large amount of non-condensation bonds of lignin, such as α-aryl, alkyl and β-aryl ether bonds. The V units of DES-L decreased, because most of the α-O-4 bond is occupied by the guaiacyl unit, and the phenolic α-O-4 bond can be rapidly degraded at the initial delignification stage [20]. The value of M(S)/m(V) is 1.85, which belongs to the typical guaiacin syringin-based lignin.…”

Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

“…with dioxane/ water) followed by precipitation yields cellulolytic enzyme lignin (CEL). 262,[311][312][313][314] The isolated yield is generally low (o35%), but the b-O-4 linkages are well preserved. 67 Alternatively, following the enzymatic hydrolysis, the insoluble material can be submitted to an additional mild acid hydrolysis step (HCl in dioxane/water), to cleave LCC linkages and solubilise lignin.…”