Total Lignin Content Research Articles

Effects of ultrasonic-alkali integrated extraction combined with Mannesi reaction on the antimicrobial properties of rice straw lignin and enhancement strategies

Lignin is one of the most abundant and underused biopolymers in nature with limited antimicrobial activities. Herein, this work aimed to enhance the antimicrobial activity of lignin extracted from waste rice straw by ultrasonic-alkali integrated extraction (USP-AT) and modify the alkali lignin through Mannich reaction to improve its antimicrobial properties. The effects of ultrasonic pretreatment (USP) time on the chemical structure, morphology, antioxidant, and antibacterial activities of lignin were studied. The results demonstrated that the total phenolic content of USP-AT lignin was higher than that of lignin extracted by alkali treatment. Moreover, the antioxidant activity of USP-AT lignin was increased by 49.69 %–69.42 %. The antibacterial activity of USP-AT lignin against Escherichia coli and Staphylococcus aureus increased by more than 40 %. However, the antibacterial capacity of USP-AT lignin is far from meeting the requirements of antibacterial food packaging. The alkali lignin was modified by Mannich reaction in order to improve its antimicrobial properties against common spoilage microorganisms or pathogenic bacteria in food and packaging. The modified USP-AT lignin exhibit remarkable antimicrobial capacities to representative bacteria, molds, and yeasts. The antifungal capacity of modified USP-AT lignin against A. niger and P. citrinum were improved by more than 40 %.

Chemical characterization of heat‐treated kraft lignin after fractionation with organic solvents and pH effect

AbstractLignin, the main source of renewable aromatics, has a complex structure, high polydispersity, and low reactivity, which hinders its large‐scale use. This study aims to improve lignin reactivity through heat treatment combined with fractionation by organic solvents or the pH effect. Heat treatment of commercial hardwood black liquor was performed at 225 °C for 150 min. The samples were then fractionated either by using organic solvents (ethyl acetate, ethanol, methanol, and acetone) or by lowering pH using hydrochloric acid (HCl) (pH values 1, 3, 5, 7, and 9). The fractionation was carried out in one step and in sequential mode. The fractionated samples were characterized chemically by the content of acid‐soluble and acid‐insoluble lignin, carbohydrates, ash, inorganic compounds (metals), elemental analysis, and by pyrolysis‐gas chromatography–mass spectrometry (Py‐GC–MS). The highest mass yields were obtained using the one‐step mode for both fractionations, with yields as high as 53.3% for organic solvents and 47.8% for the pH effect. Solvent fractionation reduced ash content by up to 75.4% and increased calorific value, carbon content, and total lignin content. Fractionation by pH effect showed an ash reduction of up to 55.9% and an increase in calorific value and carbon content of up to 8.7 MJ kg−1 and 49.7%, respectively. The Hansen solubility parameters were also calculated to address lignin's solubility in each of the tested solvents. These findings indicate that combining heat treatment and fractionation techniques improves lignin's chemical properties significantly, making it a more viable raw material for industrial use. This approach supports the circular economy by transforming lignin into a high‐value product, thereby promoting sustainable and efficient resource utilization across industries.

Insights about the use wood waste from the neotropical Amazonian for the generation of renewable energy

The abundance and availability of wood waste in the Amazon region pose a great challenge in terms of their use, such as to generate clean and renewable energy. The use of blends of the most different species constitutes a challenge in view of the energetic characteristics that are unknown for the replacement of fossil fuels. Thus, the objective of this study was to investigate the energy potential of wood waste from Amazonian species (Dinizia excelsa and from Manilkara elata, commonly used as lumber) as a way to support the generation of clean and sustainable energy. The wood waste of two Amazonian species were collected during the mechanical processing of logs; the sawdust of Eucalyptus spp. was collected in a biomass company. The contents of total extractives, total lignin, ash, moisture, bulk density, calorific value and energy density were investigated in different blends of residual biomass. The Dinizia excelsa species stood out for presenting higher values of extractives, total lignin, calorific value and energy density. The waste of Amazonian species showed satisfactory characteristics for energy use, which encourages the use of this biomass from wood processing. In addition, forest biomass waste enable the production of various compacted solid fuels, such as pellets and briquettes.

Millennial-aged organic matter preservation in anoxic and sulfidic mangrove soils: Insights from isotopic and molecular analyses

Mangrove forests are known as coastal carbon sinks, but the long-term (millennium-scale) preservation processes of organic matter (OM) in their soils and the role of sulphur in these processes are still not fully understood. These processes are crucial for better estimating the impact of sea-level variations on the carbon dynamics in mangrove forests, which are particularly sensitive to sea-level changes due to their direct hydrological interactions with coastal waters. This study focuses on a soil layer enriched in mangrove-derived OM that accumulated during a stable sea-level period of the Holocene in New Caledonia (South Pacific). Radiocarbon dating situates this enriched layer at approximately 4000 cal BP. The aim of this study is to characterize the enriched OM layer using bulk (Rock-Eval), isotopic (δ13C and δ15N), and molecular (lignin and neutral carbohydrates) analyses. This OM has undergone diagenetic processes such as dehydrogenation, and the loss of components such as the main neutral carbohydrates: glucose, xylose, and galactose. However, some Rock-Eval parameters, the total lignin content, and carbon and nitrogen isotopic ratios are characteristic of well-preserved OM, suggesting differential decomposition/preservation processes. In addition, SEM observations highlighted the presence of pyrite associated to preserved root material. Along with high Sorg/TOC ratio, these results suggest potential processes of OM sulfurization preserving it from decomposition. Prolonged sea-level stability in addition to anoxic and sulfidic soil conditions enhanced OM accumulation and long-term sequestration in mangrove soils.

Cinnamic acid derivatives played a major role in the resistance of peach leaves to Xanthomonas arboricola pv. pruni infection

AbstractPeach bacterial shot hole is a common global disease of peach trees caused by the pathogen Xanthomonas arboricola pv. pruni (Xap). To preliminarily explore the resistance mechanism of peach bacterial shot hole, leaves of the resistant variety ‘Yanbao’ and the susceptible variety ‘Frederic’ were used as test materials. The contents of total phenols, total flavonoids and lignin were analysed after 1 day of inoculation treatment, and the activities of defence enzymes and cell wall degradation enzymes in the leaves were determined. Furthermore, the resistant substances were screened by combining broad‐target metabolomics technology and in vitro antibacterial activity. The results showed that the contents of total phenols, total flavonoids and lignin in peach leaves were related to resistance. The resistant varieties resisted infection by inhibiting the activities of polygalacturonase (PG) and pectin methyl trans‐eliminase (PMTE) produced by Xap in peach leaves and increasing the activities of 4‐coumarate:coenzyme A ligase (4CL), cinnamic acid‐4‐hydroxylase (C4H), phenylalanine ammonia lyase (PAL) and peroxidase (POD). A total of six resistant compounds were screened from 85 differential metabolites. The minimum inhibitory concentrations of methyl ferulate (MF), p‐coumaric acid (p‐CA) and methyl caffeate (MC) on Xap were 0.0625, 00625 and 0.125 mg/mL, respectively, while that of the positive control drug oxytetracycline (OTC) was 0.125 mg/mL. The antibacterial activities of MF and p‐CA were better than that of OTC, and MF was equivalent to OTC. In addition, homoeriodictyol, hesperetin and fraxin have certain antibacterial effects. Before inoculation treatment, the contents of MF, p‐CA and MC in ‘Yanbao’ were 1.13, 1.24 and 1.96 times higher than those in ‘Frederic’, respectively, while they were 1.29, 1.80 and 1.94 times after inoculation treatment, respectively. During the process of pathogen infection, MF and p‐CA in the leaves of resistant peach varieties played a role in inducing resistance, while MC was a component of resistance. The above three cinnamic acid derivatives play an important roles in the resistance of peach bacterial shot hole and are potential control drugs.

Salt stress alters the cell wall components and structure in Miscanthus sinensis stems.

Miscanthus is a perennial grass suitable for the production of lignocellulosic biomass on marginal lands. The effects of salt stress on Miscanthus cell wall composition and its consequences on biomass quality have nonetheless received relatively little attention. In this study, we investigated how exposure to moderate (100 mM NaCl) or severe (200 mM NaCl) saline growing conditions altered the composition of both primary and secondary cell wall components in the stems of 15 Miscanthus sinensis genotypes. The exposure to stress drastically impacted biomass yield and cell wall composition in terms of content and structural features. In general, the observed compositional changes were more pronounced under severe stress conditions and were more apparent in genotypes with a higher sensitivity towards stress. Besides a severely reduced cellulose content, salt stress led to increased pectin content, presumably in the form of highly branched rhamnogalacturonan type I. Although salt stress had a limited effect on the total lignin content, the acid-soluble lignin content was strongly increased in the most sensitive genotypes. This effect was also reflected in substantially altered lignin structures and led to a markedly reduced incorporation of syringyl subunits and p-coumaric acid moieties. Interestingly, plants that were allowed a recovery period after stress ultimately had a reduced lignin content compared to those continuously grown under control conditions. In addition, the salt stress-induced cell wall alterations contributed to an improved enzymatic saccharification efficiency.

Zinc oxide nanoparticles alleviated vanadium-induced inhibition by regulating plant hormone signal transduction and phenylpropanoid biosynthesis in maize seedlings (Zea may L.)

Our efforts were to identify the role of zinc oxide nanoparticles (ZnO-NPs) on the growth of maize (Zea may L.) under vanadium (V) stress. Transcriptome analysis was performed on maize leaves subjected to CK, V, and V+ZnO treatments. It was found that the application of ZnO-NPs significantly reduces V accumulation and toxicity in maize. A total of 5441 and 3003 differentially expressed genes (DEGs) were identified in the CK vs. V and V+ZnO vs. V comparisons, respectively. Of these detected genes, 3016 DEGs were specific to CV vs. V, and 608 DEGs were specific to V+ZnO vs V, respectively. These genes were primarily involved in plant hormone signal transduction and phenylpropanoid biosynthesis pathways. Under V treatment, ZnO-NPs caused an up-regulation of SAUR, AUX/IAA, ARRs, GID1, and BRIIs, which resulted in high levels of IAA, CTK, GA, BRs, and JAs in maize seedlings compared to those without ZnO-NPs. The addition of ZnO-NPs also leads to a significant decrease in total phenolics and lignin contents in maize seedlings by down-regulating CCR, HCT, CAD, 4CL, and C4H genes compared to those without ZnO-NPs. Overall, the findings suggest that ZnO-NPs can improve V-induced growth suppression by changing the expression of selected genes and constitute a simple and efficient strategy for alleviating V toxicity in high-V soils.

Ectopic Production of 3,4-Dihydroxybenzoate in Planta Affects Cellulose Structure and Organization.

Lignocellulosic biomass is a highly sustainable and largely carbon dioxide neutral feedstock for the production of biofuels and advanced biomaterials. Although thermochemical pretreatment is typically used to increase the efficiency of cell wall deconstruction, genetic engineering of the major plant cell wall polymers, especially lignin, has shown promise as an alternative approach to reduce biomass recalcitrance. Poplar trees with reduced lignin content and altered composition were previously developed by overexpressing bacterial 3-dehydroshikimate dehydratase (QsuB) enzyme to divert carbon flux from the shikimate pathway. In this work, three transgenic poplar lines with increasing QsuB expression levels and different lignin contents were studied using small-angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS). SANS showed that although the cellulose microfibril cross-sectional dimension remained unchanged, the ordered organization of the microfibrils progressively decreased with increased QsuB expression. This was correlated with decreasing total lignin content in the QsuB lines. WAXS showed that the crystallite dimensions of cellulose microfibrils transverse to the growth direction were not affected by the QsuB expression, but the crystallite dimensions parallel to the growth direction were decreased by ∼20%. Cellulose crystallinity was also decreased with increased QsuB expression, which could be related to high levels of 3,4-dihydroxybenzoate, the product of QsuB expression, disrupting microfibril crystallization. In addition, the cellulose microfibril orientation angle showed a bimodal distribution at higher QsuB expression levels. Overall, this study provides new structural insights into the impact of ectopic synthesis of small-molecule metabolites on cellulose organization and structure that can be used for future efforts aimed at reducing biomass recalcitrance.

Integrated multi-omics investigation revealed the importance of phenylpropanoid metabolism in the defense response of Lilium regale Wilson to fusarium wilt.

Lilies (genus Lilium) play a significant role in the global cut-flower industry, but they are highly susceptible to fusarium wilt caused by Fusarium oxysporum. However, Lilium regale, a wild lily species, exhibits remarkable resistance to F. oxysporum. To investigate the quantitative resistance of L. regale to fusarium wilt, a comprehensive multi-omics analysis was conducted. Upon inoculation with F. oxysporum, L. regale roots showed a significant accumulation of phenylpropane metabolites, including lignin precursors, flavonoids, and hydroxycinnamic acids. These findings were consistent with the upregulated expression of phenylpropanoid biosynthesis-related genes encoding various enzymes, as revealed by transcriptomics and proteomics analyses. Furthermore, metabolomics and proteomics data demonstrated differential activation of monoterpenoid and isoquinoline alkaloid biosynthesis. Colorimetry and high-performance liquid chromatography analyses revealed significantly higher levels of total flavonoids, lignin, ferulic acid, phlorizin, and quercetin contents in L. regale scales compared with susceptible lily 'Siberia' scales during F. oxysporum infection. These phenylpropanes exhibited inhibitory effects on F. oxysporum growth and suppressed the expression of pathogenicity-related genes. Transcriptional regulatory network analysis suggested that ethylene-responsive transcription factors (ERFs) may positively regulate phenylpropanoid biosynthesis. Therefore, LrERF4 was cloned and transiently overexpressed in the fusarium wilt-susceptible Oriental hybrid lily 'Siberia'. The overexpression of LrERF4 resulted in increased levels of total flavonoids, lignin, ferulic acid, phlorizin, and quercetin, while the silencing of LrERF4 in L. regale through RNAi had the opposite effect. In conclusion, phenylpropanoid metabolism plays a crucial role in the defense response of L. regale against fusarium wilt, with LrERF4 acting as a positive regulator of phenylpropane biosynthesis.

Biochemical mechanisms preventing wilting under grafting: a case study on pumpkin rootstock grafting to wax gourd.

Wax gourd wilt is a devastating fungal disease caused by a specialized form of Fusarium oxysporum Schl. f. sp. benincasae (FOB), which severely restricts the development of the wax gourd industry. Resistant rootstock pumpkin grafting is often used to prevent and control wax gourd wilt. The "Haizhan 1" pumpkin has the characteristic of high resistance to wilt, but the mechanism through which grafted pumpkin rootstock plants acquire resistance to wax gourd wilt is still poorly understood. In this study, grafted wax gourd (GW) and self-grafted wax gourd (SW) were cultured at three concentrations [2.8 × 106 Colony Forming Units (CFU)·g-1, 8.0 × 105 CFU·g-1, and 4.0 × 105 CFU·g-1, expressed by H, M, and L]. Three culture times (6 dpi, 10 dpi, and 13 dpi) were used to observe the incidence of wilt disease in the wax gourd and the number of F. oxysporum spores in different parts of the soil and plants. Moreover, the physiological indices of the roots of plants at 5 dpi, 9 dpi, and 12 dpi in soil supplemented with M (8.0 × 105 CFU·g-1) were determined. No wilt symptoms in GW. Wilt symptoms in SW were exacerbated by the amount of FOB in the inoculated soil and culture time. At any culture time, the amount of FOB in the GW soil under the three treatments was greater than that in the roots. However, for the SW treatments, at 10 dpi and 13 dpi, the amount of FOB in the soil was lower than that in the roots. The total phenol (TP) and lignin (LIG) contents and polyphenol oxidase (PPO) and chitinase (CHI) activities were significantly increased in the GWM roots. The activities of phenylalanine ammonia lyase (PAL) and peroxidase (POD) initially decreased but then increased in the GWM roots. When the TP content decreased significantly, the LIG content and PAL and CHI activities increased initially but then decreased, whereas the PPO and POD activities did not change significantly in the SWM roots. The results indicated that the roots of the "Haizhan 1" pumpkin stock plants initiated a self-defense response after being infected with FOB, and the activities of PPO, POD, PAL, and CHI increased, and additional LIG and TP accumulated, which could effectively prevent FOB infection.

Purification of soda lignin

Purity of technical lignin is one of the main obstacles in the utilization of lignin to value-added chemicals, products, and materials. The objective of this study was to investigate and compare single and two stage purification methods for obtaining soda lignin with high purity. Extensive washing and extraction with water was found effective, increasing the abundance of acid insoluble lignin while reducing its ash content. Extraction with organic solvents was conducted with 2-propanol or blends of n-heptane/1-butanol or cyclohexane/acetone. These solvents were shown to have little effect on the total lignin content, as determined by wet-chemical methods. Two-stage treatments (washing with water followed by solvent extraction) were hence not better than single stage water extraction in terms of the lignin purity. Still, selective removal of low molecular weight components after solvent extraction was noted, reducing the overall polydispersity of the lignin. Evaporation at 40 °C also showed little effect, whereas calcination at 150 °C significantly increased the molecular weight of the soda lignin. The latter effect was explained by thermally induced cross-linking. In addition, the UV absorbance of the calcinated lignin increased, which is likely related to changes in the aromatic structure. Such effect also entailed that UV/vis spectrophotometry was found less reliable in determining the total lignin content. At last, a mathematical model was adapted to predict the total lignin content from FTIR spectrometry. In conclusion, the tested procedures can be used to purify soda lignin and adjust its molecular weight.

Lactic acid induced defense responses in tobacco against Phytophthora nicotianae

Induced resistance is considered an eco-friendly disease control strategy, which can enhance plant disease resistance by inducing the plant’s immune system to activate the defense response. In recent years, studies have shown that lactic acid can play a role in plant defense against biological stress; however, whether lactic acid can improve tobacco resistance to Phytophthora nicotianae, and its molecular mechanism remains unclear. In our study, the mycelial growth and sporangium production of P. nicotianae were inhibited by lactic acid in vitro in a dose-dependent manner. Application of lactic acid could reduce the disease index, and the contents of total phenol, salicylic acid (SA), jasmonic acid (JA), lignin and H2O2, catalase (CAT) and phenylalanine ammonia–lyase (PAL) activities were significantly increased. To explore this lactic acid-induced protective mechanism for tobacco disease resistance, RNA-Seq analysis was used. Lactic acid enhances tobacco disease resistance by activating Ca2+, reactive oxygen species (ROS) signal transduction, regulating antioxidant enzymes, SA, JA, abscisic acid (ABA) and indole-3-acetic acid (IAA) signaling pathways, and up-regulating flavonoid biosynthesis-related genes. This study demonstrated that lactic acid might play a role in inducing resistance to tobacco black shank disease; the mechanism by which lactic acid induces disease resistance includes direct antifungal activity and inducing the host to produce direct and primed defenses. In conclusion, this study provided a theoretical basis for lactic acid-induced resistance and a new perspective for preventing and treating tobacco black shank disease.

Comparison of ddRADseq and EUChip60K SNP genotyping systems for population genetics and genomic selection in Eucalyptus dunnii (Maiden).

Eucalyptus dunnii is one of the most important Eucalyptus species for short-fiber pulp production in regions where other species of the genus are affected by poor soil and climatic conditions. In this context, E. dunnii holds promise as a resource to address and adapt to the challenges of climate change. Despite its rapid growth and favorable wood properties for solid wood products, the advancement of its improvement remains in its early stages. In this work, we evaluated the performance of two single nucleotide polymorphism, (SNP), genotyping methods for population genetics analysis and Genomic Selection in E. dunnii. Double digest restriction-site associated DNA sequencing (ddRADseq) was compared with the EUChip60K array in 308 individuals from a provenance-progeny trial. The compared SNP set included 8,011 and 19,008 informative SNPs distributed along the 11 chromosomes, respectively. Although the two datasets differed in the percentage of missing data, genome coverage, minor allele frequency and estimated genetic diversity parameters, they revealed a similar genetic structure, showing two subpopulations with little differentiation between them, and low linkage disequilibrium. GS analyses were performed for eleven traits using Genomic Best Linear Unbiased Prediction (GBLUP) and a conventional pedigree-based model (ABLUP). Regardless of the SNP dataset, the predictive ability (PA) of GBLUP was better than that of ABLUP for six traits (Cellulose content, Total and Ethanolic extractives, Total and Klason lignin content and Syringyl and Guaiacyl lignin monomer ratio). When contrasting the SNP datasets used to estimate PAs, the GBLUP-EUChip60K model gave higher and significant PA values for six traits, meanwhile, the values estimated using ddRADseq gave higher values for three other traits. The PAs correlated positively with narrow sense heritabilities, with the highest correlations shown by the ABLUP and GBLUP-EUChip60K. The two genotyping methods, ddRADseq and EUChip60K, are generally comparable for population genetics and genomic prediction, demonstrating the utility of the former when subjected to rigorous SNP filtering. The results of this study provide a basis for future whole-genome studies using ddRADseq in non-model forest species for which SNP arrays have not yet been developed.

Pod-shattering characteristic differences between shattering-resistant and shattering-susceptible common vetch accessions are associated with lignin biosynthesis

The common vetch (Vicia sativa L.) is a self-pollinated annual forage legume that is widely distributed worldwide. It has wide adaptability and high nutritional value and is commonly used as an important protein source for livestock feed. However, pod shattering seriously limits the yield of common vetch. To clarify the mechanism of pod shattering in common vetch, the pod walls of three shattering-resistant (SR) accessions (B65, B135, and B392) and three shattering-susceptible (SS) accessions (L33, L170, and L461) were selected for transcriptome sequencing. A total of 17190 differentially expressed genes (DEGs) were identified in the pod wall of B135 and L461 common vetch at 5, 10, 15, 20, and 25 days after anthesis. KEGG analysis showed that “phenylpropanoid biosynthesis” was the most significantly enriched pathway, and 40 structural genes associated with lignin biosynthesis were identified and differentially expressed in B135 and L461 common vetch. We analysed the DEGs in the pod wall of three SR and three SS accessions at 15 days after anthesis, and most of the DEGs were consistent with the significant enrichment pathways identified in B135 and L461 common vetch. The total lignin content of SR accessions was significantly lower than the SS accessions. The present study lays a foundation for understanding the molecular regulatory mechanism of pod shattering related to lignin biosynthesis in common vetch and provides reference functional genes for breeders to further cultivate shattering-resistant common vetch varieties.

Comparative analyses reveal a phenylalanine ammonia lyase dependent and salicylic acid mediated host resistance in Zingiber zerumbet against the necrotrophic soft rot pathogen Pythium myriotylum

Little is known about the molecular basis of host defense in resistant wild species Zingiber zerumbet (L.) Smith against the soil-borne, necrotrophic oomycete pathogen Pythium myriotylum Drechsler, which causes the devastating soft rot disease in the spice crop ginger (Zingiber officinale Roscoe). We investigated the pattern of host defense between Z. zerumbet and ginger in response to P. myriotylum inoculation. Analysis of gene expression microarray data revealed enrichment of phenylpropanoid biosynthetic genes, particularly lignin biosynthesis genes, in pathogen-inoculated Z. zerumbet compared to ginger. RT-qPCR analysis showed the robust activation of phenylpropanoid biosynthesis genes in Z. zerumbet, including the core genes PAL, C4H, 4CL, and the monolignol biosynthesis and polymerization genes such as CCR, CAD, C3H, CCoAOMT, F5H, COMT, and LAC. Additionally, Z. zerumbet exhibited the accumulation of the phenolic acids including p-coumaric acid, sinapic acid, and ferulic acid that are characteristic of the cell walls of commelinoid monocots like Zingiberaceae and are involved in cell wall strengthening by cross linking with lignin. Z. zerumbet also had higher total lignin and total phenolics content compared to pathogen-inoculated ginger. Phloroglucinol staining revealed the enhanced fortification of cell walls in Z. zerumbet, specifically in xylem vessels and surrounding cells. The trypan blue staining indicated inhibition of pathogen growth in Z. zerumbet at the first leaf whorl, while ginger showed complete colonization of the pith within 36 h post inoculation (hpi). Accumulation of salicylic acid (SA) and induction of SA regulator NPR1 and the signaling marker PR1 were observed in Z. zerumbet. Silencing of PAL in Z. zerumbet through VIGS suppressed downstream genes, leading to reduced phenylpropanoid accumulation and SA level, resulting in the susceptibility of plants to P. myriotylum. These findings highlight the essential role of PAL-dependent mechanisms in resistance against P. myriotylum in Z. zerumbet. Moreover, our results suggest an unconventional role for SA in mediating host resistance against a necrotroph. Targeting the phenylpropanoid pathway could be a promising strategy for the effective management of P. myriotylum in ginger.

Characterization of pineapple peel (Ananas comosus) Perolera variety as a potential resource for bioethanol production

Pineapple production in Colombia generates around 185,000 tons of waste per year, consisting of peels, residual pulp, stems and leaves. Due to its lignocellulosic nature, pineapple peel shows significant potential to produce bioethanol, leading to the use of this waste. The objective of this research was to characterize the peels of pineapple (Ananas comosus) of the Perolera variety, grown in the municipality of Teorama, Catatumbo Region (Norte de Santander), to evaluate its potential for the production of bioethanol. The physical-chemical characterization of the lignocellulosic material was carried out, assessing the percentage of moisture, ash, ethanol-hexane extractables, holocellulose, cellulose, hemicellulose, and lignin soluble and insoluble in acid, each analysis was carried out in triplicate. The most relevant results obtained in the characterization were: 83.51 % moisture, holocellulose, which is made up of cellulose and hemicellulose, with percentages on a dry basis of 54.90 and 45.09 %, respectively, which indicates that a higher cellulose content means a greater amount of glucose, which facilitates the production of reducing sugars through hydrolysis processes. On the other hand, the total lignin content was 26.40 %, which contributes to structural support in the cell wall of pineapple peels, giving it rigidity and permeability. The high lignin content can make the conversion of cellulose into simple sugars difficult, which is why it is suggested to carry out a delignification process so that the cellulose is more susceptible to enzymatic hydrolysis, thus optimizing bioethanol production.

Acetyl Bromide Method for Total Lignin Content Determination in Plant Biomass.

Lignin is a tough biopolymer that gives plants strength and protection. It is also a major obstacle for converting plant biomass into biofuels because it prevents enzymes from accessing the sugar-rich fibers. To optimize biofuel production, we need to measure the lignin content in plant tissues accurately and efficiently. In this protocol, we describe a simple and reliable method to measure the total lignin content in plant tissues. The method uses acetyl bromide, a chemical that dissolves lignin into soluble derivatives and makes it possible to detect them by their absorbance at 280nm. The method consists of two steps: first, we obtained destarched cell wall material from the plant samples, and second, we treat the cell wall material with acetyl bromide and measure the absorbance of the lignin solution. This method can capture all types of lignin and works well with different plant tissues.

Preharvest Application of Melatonin Affects the Color, Strength, and Antioxidant Capacity of Pear Peels by Regulating Phenylpropane Metabolism

Melatonin is an important regulator of fruit growth and development. To explore the physiological mechanism whereby preharvest melatonin application regulates the polyphenol content of ‘Yuluxiang’ pear peel, we sprayed 0.1 mM melatonin during the first fruit expansion and early color change periods, and the control group were sprinkled with fresh water. Then, we measured the contents of anthocyanin, lignin, and major monomeric phenolics and the activities of key enzymes associated with phenolic metabolism. The results showed that melatonin application significantly increased the content of total phenolics, total flavonoids, total anthocyanins, and lignin in the peel from the color change to mature development stages. Near maturity, the activities of all key enzymes, except dihydroflavonol-4-reductase, were higher than those in the control samples, but significant differences in enzyme activity occurred at different time points. Compared with the control group, the fruit peels of the melatonin-treated plants exhibited a higher antioxidant activity and accumulated more flavonols. Thus, preharvest spraying of melatonin can alter the activity of key enzymes associated with phenolic metabolism, increasing the total phenol, flavonoid, anthocyanin, and lignin contents, which in turn, affects the color, strength, and antioxidant capacity of pear peels.

Changes in physicochemical properties and microbial community succession during leaf stacking fermentation

Leaf stacking fermentation involves enzymatic actions of many microorganisms and is an efficient and environmentally benign process for degrading macromolecular organic compounds. We investigated the dynamics of metabolite profiles, bacterial and fungal communities and their interactions during fermentation using cigar leaves from three geographic regions. The results showed that the contents of total sugar, reducing sugar, starch, cellulose, lignin, pectin, polyphenol and protein in cigar tobacco leaves was significantly decreased during fermentation. Notably, the furfural, neophytadiene, pyridine, benzyl alcohol, geranylacetone, 3-hydroxy-2-butanone, N-hexanal, 3-Methyl-1-butanol and 2,3-pentanedione were important features volatile aroma compounds during fermentation. The α-diversity of fungi and bacteria initially increased and then decreased during fermentation. An analysis of variance showed that microbial diversity was influenced by fermentation stages and growing locations, in which the all stages had greater impacts on α- and β-diversity than all regions. Microbiome profiling had identified several core bacteria including Sphingomonas, Bacillus, Staphylococcus, Pseudomonas, Ralstonia, Massilia and Fibrobacter. Fungal biomarkers included Aspergillus, Penicillium, Fusarium, Cladosporium and Trichomonascus. Interestingly, the molecular ecological networks showed that the core taxa had significant correlations with metabolic enzymes and physicochemical properties; bacteria and fungi jointly participated in the carbohydrate and nitrogen compound degrading and volatile aroma compound chemosynthesis processes during fermentation. These studies provide insights into the coupling of material conversion and microbial community succession during leaf fermentation.Graphical abstract

Citral enhances disease resistance in postharvest citrus fruit through inducing jasmonic acid pathway and accumulating phenylpropanoid compounds

Citral, a monoterpene naturally present in volatile oils of Litsea cubeba, Cymbopogon flexuosus and citrus peel, can enhance disease resistance in postharvest citrus fruit and reduce fruit decay due to Penicillium digitatum. To clarify the defense mechanism involved in the enhancement of disease resistance, RNA-seq, metabolomics and biochemical analyses were integrated to global change in citral-treated fruit. Results showed that citral fumigation was effective at controlling citrus green mold. Citral increased the activities of phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase, followed by elevated contents of total phenolics, flavonoids, and lignin. Metabolomics revealed that citral treatment triggered accumulation of the plant hormones methyl jasmonate, abscisic acid, and indoleacetic acid, and many phenylpropanoid metabolites including curcumin, cinnamyl alcohol, hesperidin, syringin, 7-methoxyflavonol, vitexin-2-O-rhamnoside, coniferin, naringin, kaempferol-7-neohesperidoside, and trans-cinnamaldehyde. RNA-seq results revealed that the expression levels of multiple genes involved in jasmonic acid (JA) profiles and phenylpropanoid biosynthesis were markedly upregulated by citral. These findings suggest that the JA pathway is positively involved in the induced disease resistance of citrus fruit by citral, and provide a novel theoretical support by which citral fumigation manages postharvest citrus green mold.