Lignin–carbohydrate complexes (LCCs) have shown antioxidant ability to scavenge the individual free radicals in vitro, while little work has been carried out to show if the LCCs can efficiently scavenge the intracellular and endogenous reactive oxygen species (ROS), which are the multiple radicals derived from the reduction of molecular oxygen during the metabolism process. In this work, carbohydrate-rich LCCs from bamboo (LCCs–B-B) and poplar (LCCs–B-P) were isolated according to the classical method, and their antioxidant activities were evaluated by scavenging intracellular ROS in RAW 264.7 cells in vitro and endogenous ROS in zebrafish in vivo. Results from composition analysis show that both LCC preparations possess similar contents of carbohydrate (52.2% and 51.2%) and lignin (44.1% and 47.8%). However, NMR analysis revealed that the LCCs–B-B contain 16.1/100C9 LCCs linkages, higher than that in LCCs–B-P (12.3/100C9). Antioxidant assays indicated that LCCs–B-B exhibited better antioxidant activities for scavenging the individual free radicals. At the cellular and animal model levels, LCCs–B-B also outperformed the performance of LCCs–B-P in scavenging the endogenous ROS in H2O2-stimulated RAW 264.7 cells in vitro and zebrafish in vivo, which may be due to its better ability to prevent the reduction of antioxidant enzyme activity (superoxide dismutase and glutathione peroxidase) in oxidative stress.

Interaction of the conjugated structure in melanin contributed to photothermal conversion. Inspired by this, here, we first demonstrated that lignin nanoparticles (L-NPs) can carry out photothermal conversion, which was attributed to π–π stacking of lignin molecules. Lignin can be readily converted into L-NPs, using the self-assembly method at room temperature. L-NPs showed a stable photothermal effect (22%). The L-NPs were successfully used to power a thermoelectric generator and drive a solar steam generation device under standard 1 sun irradiation (100 mW/cm2). Because thermoelectric generators and solar steam generation technologies have huge potential for energy generation and water purification, the as-prepared L-NPs are expected to provide an important contribution to sustainable energy and clean water production.

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The carbon quantum dot (CQD), a fluorescent carbon nanoparticle, has attracted considerable interest due to its photoluminescent property and promising applications in cell imaging and bioimaging. In this work, biocompatible, photostable, and sustainably sourced CQDs were synthesized from byproducts derived from a biorefinery process using one-pot hydrothermal treatment. The main components of byproducts were the degradation products (autohydrolyzate) of biomass pretreated by autohydrolysis. The as-synthesized CQDs had a size distribution from 2.0–6.0 nm and had high percentage of sp2 and sp3 carbon groups. The CQDs showed blue-green fluorescence with a quantum yield of ~13%, and the fluorescence behaviors were found to be stable with strong resistance to photobleaching and temperature change. In addition, it is found that the as-synthesized CQDs could be used for imaging of cells and tumors, which show potential applications in bioimaging and related fields such as phototherapy and imaging.

Background Prehydrolyzate, which is from the prehydrolysis process in dissolving pulps industry, contains various sugar-derived and lignin compounds such as xylooligosaccharides (XOS), gluco-oligosaccharides, xylose, glucose, and soluble lignin (S-L). The XOS has several beneficial effects on human physiology. XOS and S-L in prehydrolyzate are difficult to efficiently fractionate due to their similar molecular weights and water solubility. In this work, we proposed a sustainable and green process using polystyrene divinylbenzene (PS-DVB) resin to simultaneously separate and recover XOS and S-L. Enzymatic hydrolysis with endo-1,4-β-xylanase and fermentation with P. stipites were sequentially applied to purify XOS to minimize xylose content as well as amplify contents of xylobiose and xylotriose. In addition, 2D-HSQC NMR was used to analyze the structural characteristics of XOS and S-L. Furthermore, the biological abilities of antioxidants and prebiotics of these fractions were investigated by scavenging radicals and cultivating intestinally beneficial bacterias, respectively. Results Results showed that PS-DVB resin could simultaneously separate XOS and solubilized lignin with excellent yields of 93.2% and 85.3%, respectively. The obtained XOS after being purified by enzymatic hydrolysis and fermentation contained 57.7% of xylobiose and xylotriose. 10.4% amount of inherent xylan was found in the S-L fraction obtained by PS-DVB resin separation. 2D-HSQC NMR revealed that lignin carbohydrate complexes existed in both XOS and S-L as covalent linkages between lignin and 4- O -methylglucuronoarabinoxylan. The biological application results showed that the antioxidant capacity of S-L was stronger than XOS, while XOS was superior in promoting growth of intestinal Bifidobacteria adolescentis and stimulating production of short-chain fatty acids by Lactobacillus acidophilus. Conclusions The proposed strategy of sequentially combining hydrophobic resin separation, enzymatic hydrolysis, and fermentation was successfully demonstrated and resulted in simultaneous production of high-quality XOS and solubilized lignin. These biomass-derived products in prehydrolyzate can be regarded as value-adding prebiotics and antioxidants. Electronic supplementary material The online version of this article (10.1186/s13068-019-1527-3) contains supplementary material, which is available to authorized users.