Profiling of oligolignols reveals monolignol coupling conditions in lignifying poplar xylem

Lignin is an aromatic heteropolymer, abundantly present in the walls of secondary thickened cells. Although much research has been devoted to the structure and composition of the polymer to obtain insight into lignin polymerization, the low-molecular weight oligolignol fraction has escaped a detailed characterization. This fraction, in contrast to the rather inaccessible polymer, is a simple and accessible model that reveals details about the coupling of monolignols, an issue that has raised considerable controversy over the past years. We have profiled the methanol-soluble oligolignol fraction of poplar (Populus spp.) xylem, a tissue with extensive lignification. Using liquid chromatography-mass spectrometry, chemical synthesis, and nuclear magnetic resonance, we have elucidated the structures of 38 compounds, most of which were dimers, trimers, and tetramers derived from coniferyl alcohol, sinapyl alcohol, their aldehyde analogs, or vanillin. All structures support the recently challenged random chemical coupling hypothesis for lignin polymerization. Importantly, the structures of two oligomers, each containing a γ-p-hydroxybenzoylated syringyl unit, strongly suggest that sinapyl p-hydroxybenzoate is an authentic precursor for lignin polymerization in poplar

7,4'-Dihydroxyflavanone is the major Azorhizobium nod gene-inducing factor present in Sesbania rostrata seedling exudate

Exudate from Sesbania rostrata seedlings contains signaling compounds that induce the common nodABC operon of the bacterial symbiont Azorhizobium caulinodans ORS571. An Azorhizobium strain harboring a nodA::lacZ reporter fusion was used to monitor the nod-inducing activity of crude exudate fractions that were separated by reversed-phase chromatography. The major inducer was shown, by spectroscopic analysis and by comparison with chemically synthesized compounds, to be 7,4'-dihydroxyflavanone (liquiritigenin). Newly synthesized analogues, 7,3'-dihydroxyflavanone and 7,2'-dihydroxyflavanone, have only poor inducing activity

Mass spectrometry-based fragmentation as an identification tool in lignomics

The ensemble of all phenolics for which the biosynthesis is coregulated with lignin biosynthesis, i.e., metabolites from the general phenylpropanoid, monolignol, and (neo)-lignan biosynthetic pathways and their derivatives, as well as the lignin oligomers, is coined the lignome. In lignifying tissues, the lignome comprises a significant portion of the metabolome. However, as is true for metabolomics in general, the structural elucidation of unknowns represents the biggest challenge in characterizing the lignome. To minimize the necessity to purify unknowns for NMR analysis, it would be desirable to be able to extract structural information from liquid chromatography-mass spectrometry data directly. However, mass spectral libraries for metabolomics are scarce, and no libraries exist for the lignome. Therefore, elucidating the gas-phase fragmentation behavior of the major bonding types encountered in lignome-associated molecules would considerably advance the systematic characterization of the lignome. By comparative MS" analysis of a series of molecules belonging to the beta-aryl ether, benzodioxane, phenylcoumaran, and resinol groups, we succeeded in annotating typical fragmentations for each of these bonding structures as well as fragmentations that enabled the identification of the aromatic units involved in each bonding structure. Consequently, this work lays the foundation for a detailed characterization of the lignome in different plant species, mutants, and transgenics and for the MS-based sequencing of lignin oligomers and (neo)lignans

Molecular phenotyping of the pal1 and pal2 mutants of Arabidopsis thaliana reveals far-reaching consequences on phenylpropanoid, amino acid, and carbohydrate metabolism

The first enzyme of the phenylpropanoid pathway, Phe ammonia-lyase (PAL), is encoded by four genes in Arabidopsis thaliana. Whereas PAL function is well established in various plants, an insight into the functional significance of individual gene family members is lacking. We show that in the absence of clear phenotypic alterations in the Arabidopsis pall and pal2 single mutants and with limited phenotypic alterations in the pall pal2 double mutant, significant modifications occur in the transcriptome and metabolome of the pal mutants. The disruption of PAL led to transcriptomic adaptation of components of the phenylpropanoid biosynthesis, carbohydrate metabolism, and amino acid metabolism, revealing complex interactions at the level of gene expression between these pathways. Corresponding biochemical changes included a decrease in the three major flavonol glycosides, glycosylated vanillic acid, scopolin, and two novel feruloyl malates coupled to coniferyl alcohol. Moreover, Phe overaccumulated in the double mutant, and the levels of many other amino acids were significantly imbalanced. The lignin content was significantly reduced, and the syringyl/guaiacyl ratio of lignin monomers had increased. Together, from the molecular phenotype, common and specific functions of PAL1 and PAL2 are delineated, and PAL1 is qualified as being more important for the generation of phenylpropanoids

The efficacy and safety of high‐pressure processing of food

[EN]High-pressure processing (HPP) is a non-thermal treatment in which, for microbial inactivation, foods are subjected to isostatic pressures (P) of 400–600 MPa with common holding times (t) from 1.5 to 6 min. The main factors that influence the efficacy (log10 reduction of vegetative microorganisms) of HPP when applied to foodstuffs are intrinsic (e.g. water activity and pH), extrinsic (P and t) and microorganism-related (type, taxonomic unit, strain and physiological state). It was concluded that HPP of food will not present any additional microbial or chemical food safety concerns when compared to other routinely applied treatments (e.g. pasteurisation). Pathogen reductions in milk/colostrum caused by the current HPP conditions applied by the industry are lower than those achieved by the legal requirements for thermal pasteurisation. However, HPP minimum requirements (P/t combinations) could be identified to achieve specific log10 reductions of relevant hazards based on performance criteria (PC) proposed by international standard agencies (5–8 log10 reductions). The most stringent HPP conditions used industrially (600 MPa, 6 min) would achieve the above-mentioned PC, except for Staphylococcus aureus. Alkaline phosphatase (ALP), the endogenous milk enzyme that is widely used to verify adequate thermal pasteurisation of cows’ milk, is relatively pressure resistant and its use would be limited to that of an overprocessing indicator. Current data are not robust enough to support the proposal of an appropriate indicator to verify the efficacy of HPP under the current HPP conditions applied by the industry. Minimum HPP requirements to reduce Listeria monocytogenes levels by specific log10 reductions could be identified when HPP is applied to ready-to-eat (RTE) cooked meat products, but not for other types of RTE foods. These identified minimum requirements would result in the inactivation of other relevant pathogens (Salmonella and Escherichia coli) in these RTE foods to a similar or higher extent.S

The efficacy and safety of high-pressure processing of food

High-pressure processing (HPP) is a non-thermal treatment in which, for microbial inactivation, foodsare subjected to isostatic pressures (P) of 400–600 MPa with common holding times (t) from 1.5 to6 min. The main factors that influence the efficacy (log10reduction of vegetative microorganisms) ofHPP when applied to foodstuffs are intrinsic (e.g. water activity and pH), extrinsic (P and t) andmicroorganism-related (type, taxonomic unit, strain and physiological state). It was concluded thatHPP of food will not present any additional microbial or chemical food safety concerns when comparedto other routinely applied treatments (e.g. pasteurisation). Pathogen reductions in milk/colostrumcaused by the current HPP conditions applied by the industry are lower than those achieved by thelegal requirements for thermal pasteurisation. However, HPP minimum requirements (P/t combinations)could be identified to achieve specific log10reductions of relevant hazards based on performancecriteria (PC) proposed by international standard agencies (5–8 log10reductions). The most stringentHPP conditions used industrially (600 MPa, 6 min) would achieve the above-mentioned PC, except forStaphylococcus aureus. Alkaline phosphatase (ALP), the endogenous milk enzyme that is widely used to verify adequate thermal pasteurisation of cows’milk, is relatively pressure resistant and its usewould be limited to that of an overprocessing indicator. Current data are not robust enough to supportthe proposal of an appropriate indicator to verify the efficacy of HPP under the current HPP conditionsapplied by the industry. Minimum HPP requirements to reduceListeria monocytogeneslevels byspecific log10reductions could be identified when HPP is applied to ready-to-eat (RTE) cooked meatproducts, but not for other types of RTE foods. These identified minimum requirements would result inthe inactivation of other relevant pathogens (SalmonellaandEscherichia coli) in these RTE foods to asimilar or higher extent.info:eu-repo/semantics/publishedVersio

The efficacy and safety of high-pressure processing of food

High-pressure processing (HPP) is a non-thermal treatment in which, for microbial inactivation, foods are subjected to isostatic pressures (P) of 400–600 MPa with common holding times (t) from 1.5 to 6 min. The main factors that influence the efficacy (log10 reduction of vegetative microorganisms) of HPP when applied to foodstuffs are intrinsic (e.g. water activity and pH), extrinsic (P and t) and microorganism-related (type, taxonomic unit, strain and physiological state). It was concluded that HPP of food will not present any additional microbial or chemical food safety concerns when compared to other routinely applied treatments (e.g. pasteurisation). Pathogen reductions in milk/colostrum caused by the current HPP conditions applied by the industry are lower than those achieved by the legal requirements for thermal pasteurisation. However, HPP minimum requirements (P/t combinations) could be identified to achieve specific log10 reductions of relevant hazards based on performance criteria (PC) proposed by international standard agencies (5–8 log10 reductions). The most stringent HPP conditions used industrially (600 MPa, 6 min) would achieve the above-mentioned PC, except for Staphylococcus aureus. Alkaline phosphatase (ALP), the endogenous milk enzyme that is widely used to verify adequate thermal pasteurisation of cows’ milk, is relatively pressure resistant and its use would be limited to that of an overprocessing indicator. Current data are not robust enough to support the proposal of an appropriate indicator to verify the efficacy of HPP under the current HPP conditions applied by the industry. Minimum HPP requirements to reduce Listeria monocytogenes levels by specific log10 reductions could be identified when HPP is applied to ready-to-eat (RTE) cooked meat products, but not for other types of RTE foods. These identified minimum requirements would result in the inactivation of other relevant pathogens (Salmonella and Escherichia coli) in these RTE foods to a similar or higher extent.info:eu-repo/semantics/publishedVersio