Enzyme adsorption properties on dilute acid pretreated biomass by low vacuum-scanning electron microscopy and structural analysis of lignin

Unlocking lignin valorization and harnessing lignin-based raw materials for bio-manufacturing

Lignin, an energy-rich and adaptable polymer comprising phenylpropanoid monomers utilized by plants for structural reinforcement, water conveyance, and defense mechanisms, ranks as the planet's second most prevalent biopolymer, after cellulose. Despite its prevalence, lignin is frequently underused in the process of converting biomass into fuels and chemicals. Instead, it is commonly incinerated for industrial heat due to its intricate composition and resistance to decomposition, presenting obstacles for targeted valorization. In contrast to chemical catalysts, biological enzymes show promise not only in selectively converting lignin components but also in seamlessly integrating into cellular structures, offering biocatalysis as a potentially efficient pathway for lignin enhancement. This review comprehensively summarizes cutting-edge biostrategies, ligninolytic enzymes, metabolic pathways, and lignin-degrading strains or consortia involved in lignin degradation, while critically evaluating the underlying mechanisms. Metabolic and genetic engineering play crucial roles in redirecting lignin and its derivatives towards metabolic pathways like the tricarboxylic acid cycle, opening up novel avenues for its valorization. Recent advancements in lignin valorization are scrutinized, highlighting key challenges and promising solutions. Furthermore, the review underscores the importance of innovative approaches, such as leveraging digital systems and synthetic biology, to unlock the commercial potential of lignin-derived raw materials as sustainable feedstocks. Artificial intelligence-driven technologies offer promise in overcoming current challenges and driving widespread adoption of lignin valorization, presenting an alternative to sugar-based feedstocks for bio-based manufacturing in the future. The utilization of available lignin residue for synthesis of high-value chemicals or energy, even alternative food, addresses various crises looming in the food-energy-water nexus.

Inhibitory effect of flavonoid glycosides on digestive enzymes: In silico, in vitro, and in vivo studies

Flavonoid glycosides (FGs) appear to be good candidates for controlling blood glucose levels, so regular consumption of vegetables/fruits rich in FGs may prevent the consequences of type 2 diabetes (DM). Inhibition of digestive enzymes using natural FGs is a suitable dietary tool to regulate the hydrolysis of polysaccharides and overcome hyperglycemia. The aim of the current research is to find FGs that can effectively inhibit the digestive enzymes α-glucosidase (α-Gl) and α-amylase (α-Am). Accordingly, twenty-three FGs were selected and filtered through docking-based virtual screening. Based on the molecular docking and molecular dynamics (MD) simulation, among the 23 selected FGs, nicotiflorin and swertisin significantly inhibited α-Gl and α-Am, respectively. In vitro analysis revealed the inhibitory capacity of nicotiflorin on α-Gl was equal to IC50 at 0.148 mg/ml and the inhibitory activity of swertisin on α-Am was equal to IC50 at 1.894 mg/ml. It was found that nicotiflorin and swertisin act much like as a competitive inhibitor on α-Gl and α-Am, respectively. Furthermore, the fluorescence intensity of both enzymes decreased after interaction with two FGs. FT-IR and scanning electron microscopy (SEM) measurements suggested that the interactions could alter the conformation and microenvironment of the enzymes. Moreover, in vivo evaluation showed that the administration of nicotiflorin and swertisin can alleviate the blood glucose level of rats compared to the starch group (p < 0.05). The findings highlight that nicotiflorin and swertisin can be considered as possible inhibitors in treating diabetes mellitus via digestive enzymes inhibition.

Current understanding and optimization strategies for efficient lignin-enzyme interaction: A review

From energy perspective, with abundant polysaccharides (45-85%), the renewable lignocellulosic is recognized as the 2nd generation feedstock for bioethanol and bio-based products production. Enzymatic hydrolysis is a critical pathway to yield fermentable monosaccharides from pretreated substrates of lignocellulose. Nevertheless, the lignin presence in lignocellulosic substrates leads to the low substrate enzymatic digestibility ascribed to the nonproductive adsorption. It has been reported that the water-soluble lignin (low molecular weight, sulfonated/sulfomethylated and graft polymer) enhance the rate of enzymatic digestibility, however, the catalytic mechanism of lignin-enzyme interaction remains elusive. In this review, optimization strategies for enzymatic hydrolysis based on the lignin structural modification, enzyme engineering, and different additives are critically reviewed. Lignin-enzyme interaction mechanism is also discussed (lignin and various cellulases). In addition, the mathematical models and simulation of lignin, cellulose and enzyme aims for promoting an integrated biomass-conversion process for sustainable production of value-added biofuels.

Recent advances in understanding the effects of lignin structural characteristics on enzymatic hydrolysis

Enzymatic hydrolysis of lignocellulose for bioethanol production shows a great potential to remit the rapid consumption of fossil fuels, given the fact that lignocellulose feedstocks are abundant, cost-efficient, and renewable. Lignin results in low enzymatic saccharification by forming the steric hindrance, non-productive adsorption of cellulase onto lignin, and deactivating the cellulase. In general, the non-productive binding of cellulase on lignin is widely known as the major cause for inhibiting the enzymatic hydrolysis. Pretreatment is an effective way to remove lignin and improve the enzymatic digestibility of lignocellulose. Along with removing lignin, the pretreatment can modify the lignin structure, which significantly affects the non-productive adsorption of cellulase onto lignin. To relieve the inhibitory effect of lignin on enzymatic hydrolysis, enormous efforts have been made to elucidate the correlation of lignin structure with lignin-enzyme interactions but with different views. In addition, contrary to the traditional belief that lignin inhibits enzymatic hydrolysis, in recent years, the addition of water-soluble lignin such as lignosulfonate or low molecular-weight lignin exerts a positive effect on enzymatic hydrolysis, which gives a new insight into the lignin-enzyme interactions. For throwing light on their structure-interaction relationship during enzymatic hydrolysis, the effect of residual lignin in substrate and introduced lignin in hydrolysate on enzymatic hydrolysis are critically reviewed, aiming at realizing the targeted regulation of lignin structure for improving the saccharification of lignocellulose. The review is also focused on exploring the lignin-enzyme interactions to mitigate the negative impact of lignin and reducing the cost of enzymatic hydrolysis of lignocellulose.

Determination of hydroxyl groups in biorefinery resources via quantitative 31P NMR spectroscopy

The analysis of chemical structural characteristics of biorefinery product streams (such as lignin and tannin) has advanced substantially over the past decade, with traditional wet-chemical techniques being replaced or supplemented by NMR methodologies. Quantitative ³¹P NMR spectroscopy is a promising technique for the analysis of hydroxyl groups because of its unique characterization capability and broad potential applicability across the biorefinery research community. This protocol describes procedures for (i) the preparation/solubilization of lignin and tannin, (ii) the phosphitylation of their hydroxyl groups, (iii) NMR acquisition details, and (iv) the ensuing data analyses and means to precisely calculate the content of the different types of hydroxyl groups. Compared with traditional wet-chemical techniques, the technique of quantitative ³¹P NMR spectroscopy offers unique advantages in measuring hydroxyl groups in a single spectrum with high signal resolution. The method provides complete quantitative information about the hydroxyl groups with small amounts of sample (~30 mg) within a relatively short experimental time (~30-120 min).