Search Results (189)

The objective of this study was the evaluation of fungal solid-state fermentation (SSF) for the production of alginate lyase and extraction of uronic acids from Sargassum sp. For this purpose, the fungi Trichoderma asperellum, Aspergillus oryzae, and Rhizopus oryzae were applied (alone or combined) to Sargassum sp. biomass through SSF (10⁷ spores g_biomass⁻¹, 30 °C, and 7 days of treatment). In general, individual SSF with all three fungi degraded the biomass, achieving a marked synergy in the production of cellulase, laminarinase, and alginate lyase activities (especially for the last one). Trichoderma was the most efficient species in producing laminarinase, whereas Rhizophus was the best option for producing alginate lyase. However, when dual combinations were tested, the maximal values of alginate lyase activities were reached (13.4 ± 0.2 IU g_biomass⁻¹ for Aspergillus oryzae and Rhizopus oryzae). Remarkably, uronic acids were the main monomeric units from algal biomass solubilization, achieving a maximum yield of 14.4 mg_uronic g_biomass⁻¹, with the A + R condition being a feasible, eco-friendly alternative to chemical extraction of this monomer. Additionally, the application of all the fungal pretreatments drastically decreased the total phenolic content (TPC) in the biomass from 369 mg L⁻¹ to values around 44–84 mg L⁻¹, minimizing the inhibition for possible subsequent biological processes in which the residual solid can be used. Full article

Benzoxazines are a kind of high-performance thermosetting resin that can undergo ring-opening polymerization to generate cross-linking structures. Here, two benzoxazine monomers, bisphenol A/aniline type (BA-a) and bisphenol A/tert-butylamine type (BA-tb), were synthesized and mixed with three tertiary amine catalysts like 2-methylimidazole (2MI), 1,2-dimethylimidazole (12MI), 4-dimethylaminopyridine (DMAP). Differential scanning calorimetry (DSC) was performed to study the curing behaviors and the curing kinetics of two benzoxazine/catalyst systems. The results indicated that all amines had a catalytic effect on the polymerization of both benzoxazines, and the BA-a/catalyst systems showed relatively higher activity. In addition, Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra were procured to analyze structural changes in the benzoxazine/catalyst systems during the curing process. The presence of the catalysts promoted the progress of the ring-opening reactions and the formation of the phenolic units in the cross-linking structures, and these evolutions were more obvious for the BA-a/catalyst system than the BA-tb/catalyst system. Furthermore, a thermogravimetric analysis (TGA) was conducted to analyze the thermal stability of the cured systems. Finally, possible curing reaction mechanisms were proposed for these benzoxazine/amine systems. Full article

Suberin is a cell wall-associated biopolymer that possesses both poly(phenolic) and poly(aliphatic) elements assembled into chemically and spatially distinct domains. Domain-specific monomers are formed via a branched pathway between phenolic and aliphatic metabolisms. Previous transcript accumulation data (RNAseq) from early stages of wound-induced suberization revealed highly coordinated, temporal changes in the regulation of these two branches. Notably, phenolic metabolism-associated transcripts accumulated first, indicating a preference toward phenolic production early on post-wounding. To better understand the dynamics of suberin monomer biosynthesis and assembly, we assessed carbon allocation between phenolic and aliphatic metabolisms during wound-induced suberization. To do so, [¹³C₆]-glucose was administered to wound-healing potato tuber discs at different times post-wounding, and patterns of heavy carbon incorporation into (1) primary metabolites and (2) the suberin polymer were assessed. During early stages of wound-healing, carbon from glucose was rapidly incorporated into phenolic-destined metabolites, while at later stages it was shared between phenolic- and aliphatic-destined metabolites. Similarly, the pattern of labelled carbon incorporation into the poly(aliphatic) domain reflected a greater dedication of carbon towards 18:1 w-hydroxy fatty acid and 18:1 dioic acid (the two most abundant aliphatic monomers in potato suberin) later in the wound healing time course. Full article

Catalytic hydrogenolysis of lignin to produce high-value monophenols has emerged as a pivotal strategy in modern biorefineries. In this study, we synthesized spherical nitrogen-doped porous carbon (SNCB) materials by using Al/Co-BTC as a precursor, introducing melamine as a supplementary carbon and nitrogen source, and activating the material with NaOH solution. The SNCB framework was decorated with Cu-Pd bimetallic nanoparticles, exhibiting outstanding catalytic activity in the hydrogenolytic depolymerization of organosolv lignin. The Cu-Pd@SNCB catalyst exhibited remarkable activity, attributed to the hierarchical porous structure of SNCB that facilitated metal nanoparticle dispersion and reactant accessibility. The synergistic effect between Cu as the reactive site for reactant adsorption and Pd as the reactive site for H₂ adsorption enhanced the catalytic activity of the catalyst. Systematically optimized conditions (2 MPa H₂, 270 °C, 3 h) yielded 43.02 wt% phenolic monomers, with 4-(3-hydroxypropyl)-2,6-dimethoxyphenol dominating the product profile at 46.3% selectivity. The catalyst and its reaction products were analyzed using advanced characterization techniques, including XPS, XRD, TEM, SEM, BET, GC-MS, GPC, 2D HSQC NMR, and FT-IR, to elucidate the reaction mechanism. The mechanism proceeds through: (1) nucleophilic substitution of the β-O-4 hydroxyl group by MeOH, followed by (2) simultaneous hydrogenolytic cleavage of C_β-O and C_α-O bonds mediated by Cu-Pd@SNCB under H₂ atmosphere, which selectively produces 4-(3-hydroxypropyl)-2,6-dimethoxyphenol and 4-propyl-2,6-dimethoxyphenol. This study proposes a bimetallic synergistic mechanism, offering a general blueprint for developing selective lignin valorization catalysts. Full article

Three chelating monomers with an amido-β-phosphonic acid moiety in varying α-position groups (hydrogen, methyl, phenyl) were synthesized and incorporated into formo-phenolic type resin, resulting in six adsorbents. Characterization showed an increase in chelating monomer content with hydrophobicity. The materials exhibited similar maximum adsorption capacities (~170 mg/g) for uranium, with adsorption kinetics that varied with the α-groups and monomer percentage. The resins demonstrated good selectivity for uranium, and maintained significant adsorption capacities in synthetic seawater. They could be reused without loss of capacity, with the uranium recoverable in sulfuric acid solution. Full article

A rapid microwave-assisted process minimizing waste was set up to produce bio-based benzoxazine-like monomers produced from vanillylamine and melamine. Without excessive purification, different viscous liquid precursors had a remarkable ability to form four strong and transparent different solid cross-linked thermosets, displaying lower curing temperatures under 130 °C. The long and strong adhesive performance of the cured materials was observed using glass slides or aluminum surfaces and they could become a good alternative to adhesive epoxy resin for metal surfaces. At the higher temperatures, these solids could act as efficient flame-retardants proven by thermogravimetric measurements. The best candidates gave a limiting oxidation index value of 41.9. In order to improve the intrinsic surface hydrophobicity of the phenolic resins, slight amounts of silica and iron oxide nanoparticles were dispersed in the polymer matrix, and finally mechanical resistance was pointed out. The most promising of our melamine-based resin was loaded with aluminum pigment to furnish a silver-colored paste ready for being cured to afford a robust solid, which does not undergo contraction or deformation. Full article

Osmotic stress impacts the cell wall properties in plants. This study aimed to elucidate the mechanisms involved in cell wall remodeling in etiolated (dark-grown) rice (Oryza sativa L.) shoots grown under polyethylene glycol (PEG)-induced osmotic stress conditions. Shoot growth was inhibited by 70% by the treatment with 60 mM PEG for 2 days. However, when the stressed seedlings were transferred to a solution without PEG, their shoot growth rate increased significantly. A measurement of the cell wall mechanical properties revealed that the cell walls of the stressed shoots became looser and more extensible than those of unstressed shoots. Among the cell wall constituents, the amounts of cell wall-bound phenolic acids, such as ferulic acid (FA), p-coumaric acid (p-CA), and diferulic acid (DFA), per shoot and per unit of matrix polysaccharide content were significantly reduced in the stressed shoots compared to those in the unstressed shoots. Concerning the formation of cell wall-bound phenolic acids, the activity of cell wall-bound peroxidase (CW-PRX) per unit of cell wall content, which is responsible for the coupling reaction of FA to produce DFA, was 3.5 times higher in stressed shoots than in unstressed shoots, while the activity was reduced by 20% on a shoot basis in stressed shoots compared to that in unstressed shoots. The expression levels of the major class III peroxidase genes in stressed shoots were either comparable to or slightly lower than those in unstressed shoots. Conversely, the phenylalanine ammonia-lyase (PAL) activity, which contributes to the biosynthesis of FA and p-CA, was reduced by 55% and 30% on a shoot and unit-of-protein-content basis, respectively, in stressed shoots compared to that in unstressed shoots. The expression levels of abundantly expressed PAL genes decreased by 14–46% under osmotic stress. Moreover, the gene expression levels of specific BAHD acyltransferases, which are responsible for the addition of FA and p-CA to form ester-linked moieties on cell wall constituents, decreased by 15–33% under osmotic stress. These results suggest that the downregulation of the expression of specific PAL and BAHD acyltransferase genes in osmotically stressed rice shoots is responsible for a reduction in the formation of cell wall-bound phenolic acid monomers. This, in turn, may result in a decrease in the levels of DFAs. The reduction in the formation of DFA-mediated cross-linking structures within the cell wall may contribute to an increase in the mechanical extensibility of the cell wall. The remodeling of cell walls in an extensible and loosened state could assist in maintaining the growth capacity of etiolated rice shoots grown under osmotic stress and contribute to rapid growth recovery following the alleviation of osmotic stress. Full article

Thermal modification is an environmentally friendly process that does not utilize chemical agents to enhance the stability and durability of wood. The use of thermally modified wood results in a significantly extended lifespan compared with untreated wood, with minimal maintenance requirements, thereby reducing the carbon footprint. This study examines the impact of varying modification temperatures (160, 180, and 210 °C) on the lignin of spruce wood using the ThermoWood process and following the accelerated aging of thermally modified wood. Wet chemistry methods, including nitrobenzene oxidation (NBO), size exclusion chromatography (SEC), thermogravimetry (TG), differential thermogravimetry (DTG), and Fourier transform infrared spectroscopy (FTIR), were employed to investigate the alterations in lignin. At lower modification temperatures, the predominant reaction is the degradation of lignin, which results in a reduction in the molecular weight and an enhanced yield of NBO (vanillin and vanillic acid) products. At elevated temperatures, condensation and repolymerization reactions become the dominant processes, increasing these traits. The lignin content of aged wood is higher than that of thermally modified wood, which has a lower molecular weight and a lower decomposition temperature. The results demonstrate that lignin isolated from thermally modified wood at the end of its life cycle is a promising feedstock for carbon-based materials and the production of a variety of aromatic monomers, including phenols, aromatic aldehydes and acids, and benzene derivatives. Full article

Lignin is considered a renewable source for the production of valuable aromatic chemicals and liquid fuel. Solvent depolymerization of lignin is a fruitful strategy for the valorization of lignin. However, Kraft lignin is highly prone to produce char (a by-product) during the hydrothermal depolymerization process due to its poor solubility in organic solvents. Therefore, the minimization of char formation remains challenging. The purpose of the present study was to fractionate Kraft lignin in methanol to obtain low-molecular-weight fractions that could be further depolymerized in supercritical methanol to produce aromatic monomers and to suppress char formation. The results showed that the use of methanol-soluble lignin achieved a bio-oil yield of 45.04% and a char yield of 39.6% at 280 °C for 2 h compared to 28.57% and 57.73%, respectively, when using raw Kraft lignin. Elemental analysis revealed a high heating value of 30.13 MJ kg⁻¹ and a sulfur content of only 0.09% for the bio-oil derived from methanol-soluble lignin. The methanol extraction process reduced the oxygen content and increased the hydrogen and carbon contents in the modified lignin and bio-oil, indicating that the extracted lignin fraction had an enhanced deoxygenation capability and a higher energy content. These findings highlight the potential of methanol-soluble Kraft lignin as a valuable resource for sustainable energy production and the production of aromatic compounds. Full article

Various organic compounds susceptible to anodic polymerization were selected to study the effects of two solvents: acetic acid and ethyl acetate. Phenol and most of its derivatives, as well as resorcinol and 3,5-dihydroxybenzoic acid, exhibited typical electrode deactivation similar to other solvents; however, a continuous decrease in peak currents was not observed for 4-tert-butylphenols or salicylic aldehyde. Similar behavior was noted for monomers unrelated to phenols. In general, peaks were observed only for certain compounds and not in the initial voltammogram. Significant differences between the two solvents were observed in the subsequent voltammetric curves for some monomers. Microelectrode studies using 4-methoxyphenol as a model compound revealed notable differences between acetic acid and ethyl acetate in terms of curve shapes and the onset potentials of the plateaus. Plateau currents were used to estimate the solvent composition, demonstrating relatively high sensitivity to the acetic acid content. Full article

Essential oils are widely used in aromatherapy, food, and pharmaceutical industries. They contain a range of electroactive natural phenolic antioxidants like eugenol, trans-anethole, thymol, carvacrol, and vanillin. Therefore, the sensitive voltammetric determination of these compounds is of practical interest. Voltammetric sensors based on the layer-by-layer combination of carbon nanotubes and electropolymerized dyes were developed. Pyrogallol red, mixture of phenol red and p-coumaric acid, thymolphthalein, bromocresol purple were used as monomers. The created sensors were used in the quantification of target analytes using differential pulse voltammetry in a Britton–Robinson buffer. The detection limits in the range of 3.7 × 10⁻⁸–7.3 × 10⁻⁷ M were achieved. Full article

Cynanchum auriculatum Royle ex Wight (CA) is a traditional medicinal and edible plant in China. This study aimed to isolate and characterize the phenolic compounds of C. auriculatum to identify its main antioxidant constituents. Polyphenols were extracted using an ultrasound-assisted ethanol extraction method, followed by partitioning with ethyl acetate. The ethyl acetate extract was then purified through thin-layer chromatography, silica gel column chromatography, and reverse-phase silica gel column chromatography. Three monomeric compounds—cynandione A (I), 2,5-dihydroxyacetophenone (II), and radix piperacanthone (III)—were identified through their physical and chemical properties, UV and IR spectra, and liquid chromatography–mass spectrometry (LC-MS/MS). Vitamin C (VC) and 2,4-dihydroxyacetophenone were used as controls to evaluate the antioxidant potential of the two most abundant monomers. Antioxidant assays demonstrated that 2,5-dihydroxyacetophenone and cynandione A exhibited strong antioxidant activity at lower concentrations, whereas 2,4-dihydroxyacetophenone showed significantly weaker activity. Furthermore, cynandione A displayed superior cellular antioxidant activity compared to 2,5-dihydroxyacetophenone, indicating its potential as a promising bioactive compound. In conclusion, this study provides valuable insights into the phenolic composition of C. auriculatum and highlights cynandione A as a key antioxidant, paving the way for future research on its therapeutic applications. Full article

Suberin biosynthesis involves the coordinated regulation of both phenolic and aliphatic metabolisms. HXXXD/BAHD acyltransferases occupy a unique place in suberization, as they function to crosslink phenolic and aliphatic monomers during suberin assembly. To date, only one suberin-associated HXXXD/BAHD acyltransferase, StFHT, has been described in potatoes, whereas, in Arabidopsis, at least two are implicated in suberin biosynthesis. RNAseq data from wound-induced potato tubers undergoing suberization indicate that transcripts for 28 HXXXD/BAHD acyltransferase genes accumulate in response to wounding. In the present study, we generated RNAi knockdown lines for StFHT and another highly wound-induced HXXXD/BAHD acyltransferase, designated StHCT, and characterized their wound-induced suberin phenotype. StFHT-RNAi and StHCT-RNAi knockdown lines share the same aliphatic suberin phenotype of reduced esterified ferulic acid and ferulates, which is similar to the previously described StFHT-RNAi knockdown suberin phenotype. However, the phenolic suberin phenotype differed between the two knockdown genotypes, with StHCT-RNAi knockdown lines having proportionately more p-hydroxyphenyl-derived moieties than either StFHT-RNAi knockdown or empty vector control lines. Analysis of soluble polar metabolites revealed that StHCT catalyzes a step upstream from StFHT. Overall, our data support the involvement of more than one HXXXD/BAHD acyltransferase in potato suberin biosynthesis. Full article

The effect of oak chips on the phenolic composition, color characteristics, and antioxidant capacity of Bobal red wines caused by contact with oak chips at different stages of the winemaking process has been studied. Performance liquid chromatography–diode array detection (HPLC-DAD) was used to determine the detailed phenolic composition of wines and antioxidant activity, and chromatic characteristics were determined by spectrophotometric methods. Standard red winemaking process was applied to make the Bobal control wine. The rest of the wines were elaborated with oak chip contact at two dose levels (3 and 6 g/L) in different phases of the winemaking process: during alcoholic fermentation (AF), during malolactic fermentation (MLF), and in young wines. The phenolic composition, antioxidant activity, and chromatic characteristics of Bobal control wines were slightly but significantly modified by contact with the oak chips. Wines in contact with oak chips during malolactic fermentation showed a decrease in the concentration of resveratrol-monomer stilbenes, monomeric anthocyanins, and pyranoanthocyanins. In general, the concentration of total resveratrol is influenced by the dose level used, resulting in a 10% decrease when the dose level is 6 g/L compared to the 3 g/L dose. Full article

Asynchronous ripening is a significant challenge in winemaking. Green berries reduce alcohol and pH while increasing acidity. Green berries are rich in bitter and astringent compounds, with an unknown impact on wine quality. The aim of this study was to evaluate the impact of harvest date and vineyard location on the polyphenolic composition of Plavac Mali wines in Dalmatia, Croatia. Experiments were conducted in two locations, Split and Zadar, producing fifteen wines per location from four harvest dates (H1–H4), including green berry wines from H1. The first harvest date occurred 27 days after véraison (DAV) and the last at 69 DAV, corresponding to overripeness. Green berry wines of H1 had low alcohol content up to 4.4% (v/v) in Split. Epigallocatechin was the main flavonoid in those wines, followed by dimer B1 in Split and catechin in Zadar. Green wines from Split had a higher concentration of phenolic acids, flavan-3-ol monomers and dimers. Wines of H3 had the highest concentration of malvidin-3-O-glucoside. With a later harvest date, a dramatic decrease in catechin and dimers was observed in wines from Split, and a decrease in epicatechin, epigallocatechin and dimer B1 in those from Zadar. The final expression of the physiochemical and polyphenolic composition of Plavac Mali wine is determined by the dynamics of harvest date, location and their interactions. Full article