Correlation between lignin physicochemical properties and inhibition to enzymatic hydrolysis of cellulose

Abstract

Using isolated organosolv lignins from hardwood poplar and softwood lodgepole pine with varied physicochemical properties (molecular weight, aliphatic hydroxyl, phenolic hydroxyl, and hydrophobicity), the inhibitory effect of the lignins on enzymatic hydrolysis of cellulose was investigated and the relationship between lignin properties and the inhibitory effect was elucidated. The results indicated that the lignin inhibition to enzymatic hydrolysis of cellulose was closely related to the hydrophobicity and the phenolic hydroxyl groups of the lignin. The overall hydrophobicity of the lignin quantified by contact angle could serve as a predictor of the inhibitory effect of lignin. Hydrophilic modification of the lignin by carboxylation and sulfonation reduced the hydrophobicity by 22-30% and thereby removed the lignin inhibition by 76-96%. Phenolic hydroxyl group was a crucial factor affecting the inhibitory effect of lignin. Blocking free phenolic hydroxyl group by chemical reaction such as hydroxypropylation significantly (65-91%) reduced the inhibitory effect of lignin. Biotechnol. Bioeng. 2016;113: 1213-1224. © 2015 Wiley Periodicals, Inc.

Current Understanding of the Correlation of Lignin Structure with Biomass Recalcitrance

“…Lignin condensation associated with hydrophobicity influences lignin-enzyme interactions significantly. A few studies have shown that lignin with increased condensation from pretreated biomass tended to adsorb more enzymes, resulting in more inhibitory to cellulose hydrolysis (Yu et al, 2014; Ko et al, 2015; Huang et al, 2016; Yang and Pan, 2016). …”

“…Lignin with increased Ar-OH had higher enzyme affinity thereof more inhibition to the hydrolysis of Avicel (Rahikainen et al, 2013; Guo et al, 2014). Yang and Pan recently found that Ar-OH (3.5–4.4 mmol/g lignin) blocked by hydroxypropylation had negligible effect on enzyme adsorption, however, reduced lignin inhibition significantly, which suggested Ar-OH was more related with other interaction for inhibitory effect (Yang and Pan, 2016). Carboxylic groups (COOH) in lignin alter the physicochemical effects of lignin by (i) increasing hydrophilicity; (ii) creating electrostatic charge; and (iii) enhancing hydrogen bond, which could impact lignin- enzyme interactions differently (Nakagame et al, 2011a).…”

“…Increased COOH in lignin enhanced the hydrolysis efficiency of Avicel as COOH may alleviate the non-productive binding by increasing hydrophilicity and electrostatic repulsion force of lignin to enzymes (Nakagame et al, 2011b; Moxley et al, 2012). Increasing the hydrophilicity of lignin via carboxylation and sulfonation reduced inhibitory effect substantially (Yang and Pan, 2016). However, the correlation of Ar-OH and COOH with enzymatic hydrolysis becomes complicated when different botanical origins and pretreatment methods are used due to the complexity of substrates.…”

“…The molecular weight of alkali lignin and lignosulfonate had an opposite effect on enzymatic hydrolysis (Zhou et al, 2013; Li Y. et al, 2016) and no clear impact of the molecular weights on enzyme adsorption was found (Pareek et al, 2013; Guo et al, 2014). Although earlier study indicated that lignin with lower polydispersity thereby higher plasticity, interacts favorably with proteins (Berlin et al, 2006), a few recent reports had difficulty to correlate lignin polydispersity with saccharification/enzyme adsorption (Pareek et al, 2013; Guo et al, 2014; Yang and Pan, 2016). …”

Physicochemical Structural Changes of Cellulosic Substrates during Enzymatic Saccharification

“…To better understand the effect of lignin on non-productive enzyme binding, various lignins have been tested [46][47][48][49][50][51][52]. Table 3 summarizes the adsorption parameters of enzymes onto differently prepared lignins in the recent studies.…”