The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
David A. Brummell - One of the best experts on this subject based on the ideXlab platform.
-
Cell wall disassembly in ripening fruit
Functional Plant Biology, 2006Co-Authors: David A. BrummellAbstract:Fruit softening during ripening involves a coordinated series of modifications to the polysaccharide components of the primary cell wall and middle lamella, resulting in a weakening of the structure. Degradation of polysaccharides and alterations in the bonding between polymers cause an increase in cell separation and a softening and swelling of thewall,which, combined with alterations in turgor, bring about fruit softening and textural changes. A wide range in the extent of cell wall pectic modifications has been observed between species, whereas the Depolymerisation of xyloglucan is relatively limited and more consistent. The earliest events to be initiated are usually a loss of pectic galactan side chains and the Depolymerisation of matrix glycans, which may begin before ripening, followed by a loss of pectic arabinan side chains and pectin solubilisation. The Depolymerisation of pectins may begin during early to mid-ripening, but is usually most pronounced late in ripening. However, some of these events may be absent or occur at very low levels in some species. Cell wall swelling may be related to a loosening of the xyloglucan–cellulose network and to pectin solubilisation, and these processes combined with the loss of pectic side chains increase wall porosity. An increase in wall porosity later in ripening may allow increased access of degradative enzymes to their substrates.
-
Cell wall metabolism during maturation, ripening and senescence of peach fruit
Journal of Experimental Botany, 2004Co-Authors: David A. Brummell, Valeriano Dal Cin, Carlos H Crisosto, John M. LabavitchAbstract:Cell wall changes were examined in fruit of a melting flesh peach (Prunus persica L.) allowed to ripen on the tree. Three phases to softening were noted, the first of which began prior to the completion of flesh colour change and an increase in ethylene evolution. Softening in young mature fruit, prior to ripening, was associated with a depolymerization of matrix glycans both loosely and tightly attached to cellulose and a loss of Gal from all cell wall fractions. After the initiation of ripening, but before the melting stage, softening was associated with continuing, progressive depolymerization of matrix glycans. A massive loss of Ara from the loosely bound matrix glycan fraction was observed, probably from side chains of glucuronoarabinoxylan, pectin, or possibly arabinogalactan protein firmly bound into the wall and solubilized in this extract. An increase in the solubilization of polyuronides also occurred during this period, when softening was already well advanced. The extensive softening of the melting period was marked by substantial depolymerization of both loosely and tightly bound matrix glycans, including a loss of Ara from the latter, an increase in matrix glycan extractability, and a dramatic depolymerization of chelator-soluble polyuronides which continued during senescence. Depolymerization of chelator-soluble polyuronides thus occurred substantially after the increase in their solubilization. Ripening-related increases were observed in the activities of exo- and endo-polygalacturonase (EC 3.2.1.67; EC 3.2.1.15), pectin methylesterase (EC 3.1.1.11), endo-1,4-beta-glucanase (EC 3.2.1.4), endo-1,4-beta-mannanase (EC 3.2.1.78), alpha-arabinosidase (EC 3.2.1.55), and beta-galactosidase (EC 3.2.1.23), but the timing and extent of the increases differed between enzymes and was not necessarily related to ethylene evolution. Fruit softening in peach is a continuous process and correlated closely with the depolymerization of matrix glycans, which proceeded throughout development. However, numerous other cell wall changes also took place, such as the deglycosylation of particular polymers and the solubilization and depolymerization of chelator-soluble polyuronides, but these were transient and occurred only at specific phases of the softening process. Fruit softening and other textural changes in peach appear to have a number of stages, each involving a different set of cell wall modifications.
-
Cell wall metabolism in fruit softening and quality and its manipulation in transgenic plants
Plant Molecular Biology, 2001Co-Authors: David A. Brummell, Mark H. HarpsterAbstract:Excessive softening is the main factor limiting fruit shelf life and storage. Transgenic plants modified in the expression of cell wall modifying proteins have been used to investigate the role of particular activities in fruit softening during ripening, and in the manufacture of processed fruit products. Transgenic experiments show that polygalacturonase (PG) activity is largely responsible for pectin depolymerization and solubilization, but that PG-mediated pectin depolymerization requires pectin to be de-methyl-esterified by pectin methylesterase (PME), and that the PG beta-subunit protein plays a role in limiting pectin solubilization. Suppression of PG activity only slightly reduces fruit softening (but extends fruit shelf life), suppression of PME activity does not affect firmness during normal ripening, and suppression of beta-subunit protein accumulation increases softening. All these pectin-modifying proteins affect the integrity of the middle lamella, which controls cell-to-cell adhesion and thus influences fruit texture. Diminished accumulation of either PG or PME activity considerably increases the viscosity of tomato juice or paste, which is correlated with reduced polyuronide depolymerization during processing. In contrast, suppression of beta-galactosidase activity early in ripening significantly reduces fruit softening, suggesting that the removal of pectic galactan side-chains is an important factor in the cell wall changes leading to ripening-related firmness loss. Suppression or overexpression of endo-(1-->4)beta-D-glucanase activity has no detectable effect on fruit softening or the depolymerization of matrix glycans, and neither the substrate nor the function for this enzyme has been determined. The role of xyloglucan endotransglycosylase activity in softening is also obscure, and the activity responsible for xyloglucan depolymerization during ripening, a major contributor to softening, has not yet been identified. However, ripening-related expansin protein abundance is directly correlated with fruit softening and has additional indirect effects on pectin depolymerization, showing that this protein is intimately involved in the softening process. Transgenic work has shown that the cell wall changes leading to fruit softening and textural changes are complex, and involve the coordinated and interdependent activities of a range of cell wall-modifying proteins. It is suggested that the cell wall changes caused early in ripening by the activities of some enzymes, notably beta-galactosidase and ripening-related expansin, may restrict or control the activities of other ripening-related enzymes necessary for the fruit softening process.
Johan P M Sanders - One of the best experts on this subject based on the ideXlab platform.
-
lignin Depolymerisation in supercritical carbon dioxide acetone water fluid for the production of aromatic chemicals
Bioresource Technology, 2012Co-Authors: Richard J A Gosselink, Wouter Teunissen, Ed De Jong, Goran Gellerstedt, Elinor L Scott, Johan P M SandersAbstract:Valorisation of lignin plays a key role in further development of lignocellulosic biorefinery processes the production of biofuels and bio-based materials. In the present study, organosolv hardwood and wheat straw lignins were converted in a supercritical fluid consisting of carbon dioxide/acetone/water (300–370 °C, 100 bar) to a phenolic oil consisting of oligomeric fragments and monomeric aromatic compounds with a total yield of 10–12% based on lignin. These yields are similar to the state-of-the-art technologies such as base-catalysed thermal processes applied for lignin Depolymerisation. Addition of formic acid increases the yield of monomeric aromatic species by stabilizing aromatic radicals. Supercritical Depolymerisation of wheat straw and hardwood lignin yielded monomeric compounds in different compositions with a maximum yield of 2.0% for syringic acid and 3.6% for syringol, respectively. The results of the present study showed that under the applied conditions competition occurred between lignin Depolymerisation and recondensation of fragments.
-
Lignin Depolymerisation in supercritical carbon dioxide/acetone/water fluid for the production of aromatic chemicals.
Bioresource Technology, 2011Co-Authors: Richard J A Gosselink, Wouter Teunissen, Ed De Jong, Goran Gellerstedt, Elinor L Scott, Johan P M SandersAbstract:Valorisation of lignin plays a key role in further development of lignocellulosic biorefinery processes the production of biofuels and bio-based materials. In the present study, organosolv hardwood and wheat straw lignins were converted in a supercritical fluid consisting of carbon dioxide/acetone/water (300–370 °C, 100 bar) to a phenolic oil consisting of oligomeric fragments and monomeric aromatic compounds with a total yield of 10–12% based on lignin. These yields are similar to the state-of-the-art technologies such as base-catalysed thermal processes applied for lignin Depolymerisation. Addition of formic acid increases the yield of monomeric aromatic species by stabilizing aromatic radicals. Supercritical Depolymerisation of wheat straw and hardwood lignin yielded monomeric compounds in different compositions with a maximum yield of 2.0% for syringic acid and 3.6% for syringol, respectively. The results of the present study showed that under the applied conditions competition occurred between lignin Depolymerisation and recondensation of fragments.
Richard J A Gosselink - One of the best experts on this subject based on the ideXlab platform.
-
lignin Depolymerisation in supercritical carbon dioxide acetone water fluid for the production of aromatic chemicals
Bioresource Technology, 2012Co-Authors: Richard J A Gosselink, Wouter Teunissen, Ed De Jong, Goran Gellerstedt, Elinor L Scott, Johan P M SandersAbstract:Valorisation of lignin plays a key role in further development of lignocellulosic biorefinery processes the production of biofuels and bio-based materials. In the present study, organosolv hardwood and wheat straw lignins were converted in a supercritical fluid consisting of carbon dioxide/acetone/water (300–370 °C, 100 bar) to a phenolic oil consisting of oligomeric fragments and monomeric aromatic compounds with a total yield of 10–12% based on lignin. These yields are similar to the state-of-the-art technologies such as base-catalysed thermal processes applied for lignin Depolymerisation. Addition of formic acid increases the yield of monomeric aromatic species by stabilizing aromatic radicals. Supercritical Depolymerisation of wheat straw and hardwood lignin yielded monomeric compounds in different compositions with a maximum yield of 2.0% for syringic acid and 3.6% for syringol, respectively. The results of the present study showed that under the applied conditions competition occurred between lignin Depolymerisation and recondensation of fragments.
-
Lignin Depolymerisation in supercritical carbon dioxide/acetone/water fluid for the production of aromatic chemicals.
Bioresource Technology, 2011Co-Authors: Richard J A Gosselink, Wouter Teunissen, Ed De Jong, Goran Gellerstedt, Elinor L Scott, Johan P M SandersAbstract:Valorisation of lignin plays a key role in further development of lignocellulosic biorefinery processes the production of biofuels and bio-based materials. In the present study, organosolv hardwood and wheat straw lignins were converted in a supercritical fluid consisting of carbon dioxide/acetone/water (300–370 °C, 100 bar) to a phenolic oil consisting of oligomeric fragments and monomeric aromatic compounds with a total yield of 10–12% based on lignin. These yields are similar to the state-of-the-art technologies such as base-catalysed thermal processes applied for lignin Depolymerisation. Addition of formic acid increases the yield of monomeric aromatic species by stabilizing aromatic radicals. Supercritical Depolymerisation of wheat straw and hardwood lignin yielded monomeric compounds in different compositions with a maximum yield of 2.0% for syringic acid and 3.6% for syringol, respectively. The results of the present study showed that under the applied conditions competition occurred between lignin Depolymerisation and recondensation of fragments.
Kristoffer Tømmeraas - One of the best experts on this subject based on the ideXlab platform.
-
Thermal degradation and stability of sodium hyaluronate in solid state
Carbohydrate Polymers, 2014Co-Authors: Mikael Bjerg Caspersen, Johannes P. Roubroeks, Ruidong Zhao, Qun Liu, Jens Fogh, Shan Huang, Kristoffer TømmeraasAbstract:The kinetics and mechanism of Depolymerisation of solid sodium hyaluronate at elevated temperatures and various pH have been investigated. Depolymerisation was found to be governed by random chain scission. The activation energy at neutral pH was found to be 127 kJ/mol. The solid polymer was most stable at neutral pH. Results suggest the Depolymerisation mechanism in solid- and solution state to be the same. Correlation of log intrinsic viscosity to log weight-average molecular weight was investigated to ensure high quality data for polymer size. Based on more than sixty hyaluronate samples spanning from 0.4 to 2.3 MDa, it was concluded that a second order polynomial regression gives a better fit than the linear regression offered by classical Mark-Houwink-Kuhn- Sakurada description. This finding was supported by literature data and could be expanded to other simple, well behaving linear polymers, such as polystyrene and polyethylene. ?? 2014 Elsevier Ltd. All rights reserved.
Stephan Drusch - One of the best experts on this subject based on the ideXlab platform.
-
thermal degradation of citrus pectin in low moisture environment investigation of backbone Depolymerisation
Food Hydrocolloids, 2020Co-Authors: Ulrike Einhornstoll, Hanna Kastner, Alexandra Fatouros, Andrea Krahmer, Lothar W Kroh, Stephan DruschAbstract:Abstract Thermal degradation of modified pectin samples with varying molecular structure during storage was recently studied at 60 °C and 80% relative humidity (rh) for 28 days. Demethoxylation and Depolymerisation were identified as main degradation reactions. The present paper aims on improving the understanding of the different Depolymerisation reactions and their interplay with demethoxylation during storage. Therefore, thermal degradaton of acidic and alkaline demethoxylated pectins was studied at a further reduced rh of 40%. The alterations were examined in detail via molecular parameters and were reflected by Differential scanning calorimetry and attenuated total reflectance Fourier-transformation infrared spectroscopy. The impact of thermal degradation on pectin particle structure was studied via particle surface area and microscopy. At low relative humidity (rh) demethoxylation and Depolymerisation were reduced, and the formation of brown reaction products, resulting from further decomposition of intermediate uronides and neutral sugars, was restricted. By comparing thermal degradation at different humidity, eliminative decarboxylation was identified as the main Depolymerisation reaction. Reduction of rh affected also the alteration of pectin material properties, particle surface reduction was less pronounced. Molecular alterations were stronger in case of acidic demethoxylated samples, and alterations of material properties were higher in case of alkaline demethoxylated samples.
-
Thermal degradation of citrus pectin in low-moisture environment – Investigation of backbone Depolymerisation
Food Hydrocolloids, 2020Co-Authors: Ulrike Einhorn-stoll, Hanna Kastner, Alexandra Fatouros, Andrea Krahmer, Lothar W Kroh, Stephan DruschAbstract:Abstract Thermal degradation of modified pectin samples with varying molecular structure during storage was recently studied at 60 °C and 80% relative humidity (rh) for 28 days. Demethoxylation and Depolymerisation were identified as main degradation reactions. The present paper aims on improving the understanding of the different Depolymerisation reactions and their interplay with demethoxylation during storage. Therefore, thermal degradaton of acidic and alkaline demethoxylated pectins was studied at a further reduced rh of 40%. The alterations were examined in detail via molecular parameters and were reflected by Differential scanning calorimetry and attenuated total reflectance Fourier-transformation infrared spectroscopy. The impact of thermal degradation on pectin particle structure was studied via particle surface area and microscopy. At low relative humidity (rh) demethoxylation and Depolymerisation were reduced, and the formation of brown reaction products, resulting from further decomposition of intermediate uronides and neutral sugars, was restricted. By comparing thermal degradation at different humidity, eliminative decarboxylation was identified as the main Depolymerisation reaction. Reduction of rh affected also the alteration of pectin material properties, particle surface reduction was less pronounced. Molecular alterations were stronger in case of acidic demethoxylated samples, and alterations of material properties were higher in case of alkaline demethoxylated samples.