CDTA-soluble Pectin Research Articles

Extraction of cell wall pectins and hemicellulose from agro-industrial wastes: A sustainable alternative source

The efficient repurposing of agro-industrial waste has significantly enhanced the utilization of food resources. This study aims to propose a methodology for extracting cell wall polysaccharides from residues of mango (Mangifera indica), passion fruit (Passiflora edulis), and cashew (Anacardium occidentale). Polysaccharide fractions were obtained through sequential extraction protocols involving water, cyclohexane-trans-1,2-diamine tetracetate (CDTA), sodium carbonate:CDTA, and potassium hydroxide. These fractions were categorized as water-soluble pectin (WSP), CDTA-soluble pectin (CSP), sodium carbonate-soluble pectin (SSP), and hemicellulose (HC), respectively. Each polysaccharide fraction was characterized by Nuclear Magnetic Resonance (NMR) spectroscopy and Gel Permeation Chromatography (GPC). Monosaccharide composition was determined using Gas Chromatography-Mass Spectrometry (GC–MS). NMR spectra of WSP, CSP, and SSP fractions exhibited characteristic pectin features, while the HC fraction primarily comprised hemicellulose. Consequently, the proposed methodology demonstrates potential as a standardized protocol for the extraction of pectin and hemicellulose from various food sources.

Improving enzyme accessibility in the aqueous enzymatic extraction process by microwave-induced porous cell walls to increase oil body and protein yields

Aqueous enzymatic extraction (AEE) is a green and sustainable extraction method. However, the intact cell wall hinders the accessibility of enzymes, severely limiting the efficiency and application of the AEE method. In this study, microwave-assisted aqueous enzymatic extraction (MAAEE) was used to degrade the peanut cell wall and improve the yield of oil and protein. Transmission electron microscopy, scanning electron microscopy, BET-specific surface area, Fourier transform infrared spectroscopy, X-ray diffraction, and chemical composition analysis were used to characterize the structure and chemical changes of the peanut cell wall. The results showed that microwave treatment could break the structure of the peanut cell wall, increase the porosity of raw materials, accelerate the efficiency of enzymatic hydrolysis, and promote the extraction of oil and protein. Compared with raw peanut powder (MC-0), microwaved peanut powder (MC-4) had a higher oil body yield (>44%) and protein release rate (>76%). At the microscopic level, cell wall rupture, oil accumulation, and cell contents scattered outside the cell were observed. The mean pore size, pore volume, and specific surface area increased by 54.1%, 149.4%, and 63.5%, respectively, while the crystallinity decreased by 4.4%. The content of hemicellulose and CDTA-soluble pectin (CSP) decreased by 18.6% and 32.9%, respectively. The degradation rates of cellulase and pectinase on cell wall components were significantly increased by 8.5%–43.2% (p < 0.05). In summary, microwave-induced porous cell walls could significantly improve enzyme accessibility, accelerate enzymatic hydrolysis efficiency, and promote oil and protein extraction.

Cold shock precooling improves the firmness of chili pepper during postharvest storage and the molecular mechanisms related to pectin.

This research was conducted to explore the influence of cold shock on the firmness, a quality marker in chili pepper during 0-21 d storage and determine mechanism by cold shock impacted pectin. Chili peppers were exposed to cold shock precooling (0±2°C water/ice mixture) for 0-, 30-, 90- and 150-min, respectively. Results showed that cold shock alleviated loss of firmness throughout storage. Firmness was positively associated with sodium carbonate-soluble pectin content (r=0.44), methylation degree of CDTA-soluble pectin (r=0.82) and water-soluble pectin (WSP, r=0.87), but negatively associated with WSP content (r=-0.76), and the activities of β-galactosidase (r=-0.72) and pectinlyase (r=-0.74). Cold shock for 90min was determined to be optimal. This study confirms the applicability of cold shock precooling to maintain firmness and thereby to extend the shelf life of chili pepper.

Shelf-life prediction of fresh ginseng packaged with plastic films based on a kinetic model and multivariate accelerated shelf-life testing

The purpose of this study was to monitor changes in the quality of ginseng and predict its shelf-life. As the storage period of ginseng increased, some quality indicators, such as water-soluble pectin (WSP), CDTA-soluble pectin (CSP), cellulose, weight loss, and microbial growth increased, while others (Na2CO3-soluble pectin/NSP, hemicellulose, starch, and firmness) decreased. Principal component analysis (PCA) was performed using the quality attribute data and the principal component 1 (PC1) scores extracted from the PCA results were applied to the multivariate analysis. The reaction rate at different temperatures and the temperature dependence of the reaction rate were determined using kinetic and Arrhenius models, respectively. Among the kinetic models, zeroth-order models with cellulose and a PC1 score provided an adequate fit for reaction rate estimation. Hence, the prediction model was constructed by applying the cellulose and PC1 scores to the zeroth-order kinetic and Arrhenius models. The prediction model with PC1 score showed higher R2 values (0.877-0.919) than those of cellulose (0.797-0.863), indicating that multivariate analysis using PC1 score is more accurate for the shelf-life prediction of ginseng. The predicted shelf-life using the multivariate accelerated shelf-life test at 5, 20, and 35°C was 40, 16, and 7 days, respectively.

Dielectric barrier discharge plasma delayed the textural hardening of bamboo shoots by regulating cell wall metabolism

Postharvest bamboo shoots may undergo a hardening process even under low-temperature storage. Dielectric barrier discharge plasma (DBDP) is a promising non-thermal preservation technology, which reportedly delays senescence and improves the texture of plants. The influences of DBDP treatment on the changes of quality attributes, cell wall components, and cell wall modifying enzymes in Lei bamboo (Phyllostachys praecox) shoots were investigated. DBDP treatment improved the shelf life, texture, and energy level while decreasing the cell membrane permeability, malondialdehyde content, and hydrogen peroxide contents of bamboo shoots. DBDP treatment obtained a higher ratio of water-soluble pectin to CDTA-soluble pectin contents as well as lower levels of cellulose and hemicellulose contents by regulating the cell wall modifying enzymes, inhibiting the self-assembly of pectin gels and cellulose-xyloglucan networks. Scanning and transmission electron microscopy showed that DBDP treatment slightly destabilized the cell wall and inhibited secondary cell wall formation. The results showed that DBDP treatment inhibited the hardening process and maintained a better texture of bamboo shoots under low-temperature storage.

Reduced degradation of the cell wall polysaccharides maintains higher tissue integrity of papaya (Carica papaya L.) during chilling storage

Papaya (Carica papaya L.) fruit are vulnerable to chilling injury (CI), and the symptoms of CI develop more intensively when the fruit are stored at 6 ℃ rather than 1 ℃. This is considered to be abnormal CI behavior of papaya fruit, a phenomenon that is unclear but thought to be related to cell wall metabolism. Thus, this study examined the relationship between the development of CI and alterations of the cell wall metabolism in papaya fruit stored at 1 ºC and 6 ℃. The 1 ℃-storage maintained the integrity of the papaya exocarp and alleviated the development of CI and the loss of free moisture. Ultrastructural observations demonstrated that the middle lamellae were denser in papaya fruit stored at 1 ℃ than those in 6 ℃-storage, which alleviated the disintegration of cell wall at 1 ℃-storage. Compared with 6 ℃-storage, 1 ℃-storage inhibited the degradation of Na2CO3-soluble pectin, CDTA-soluble pectin, and cellulose. The 1 ℃-storage also delayed the solubilization of water-soluble pectin and the transformation of 24% KOH-soluble fraction to the 4% KOH-soluble fraction. Lower activities of cell wall-modifying enzymes, including pectin methylesterase, polygalacturonase, pectate lyase, β-galactosidase, xyloglucan endotransglycosylase, and cellulase, were observed in papaya fruit stored at 1 ℃. These results suggest that alleviating the degradation of cell wall polysaccharides maintains higher tissue integrity in papaya fruit during chilling storage.

1-methylcyclopropene treatment improves chilling tolerance by regulating IAA biosynthesis, auxin signaling transduction and cell wall degradation in peach fruit

Chilling injury (CI) is a major issue in peach fruit during cold storage, which can be alleviated by 1-methylcyclopropene (1-MCP) treatment. Previous works have focused on ethylene regualtion. Recently, auxin signals were found to play vital roles in both 1-MCP-regulated fruit ripening and cold resistance. However, the information regarding the relationship between auxin metabolism and 1-MCP-induced cold tolerance was still limited, especially in cold-sensitive fruit. To investigate the underlying mechanisms, we performed transcriptome analysis and found that 1-MCP treatment significantly regulated several metabolic pathways, including auxin signaling, cell wall pectin degradation, and indole pyruvate metabolism. This regulation contribute to the development of cold resistance by maintaining cell wall structural integrity through delaying the increase of water-soluble pectin (WSP) and the decrease of CDTA-soluble pectin (CSP) and sodium carbonate-soluble pectin (NSP). Accordingly, 1-MCP treatment reduced the activities of polygalacturonase (PG), pectin methylesterase (PME) and pectin lyase (PEL), and down-regulated the expressions of PpPG1, PpPG2, PpPME1, PpPME2, PpPEL1 and PpPEL2. Moreover, the treatment decreased indole-3-acetic acid (IAA) biosynthesis via the indole pyruvate pathway, which led to the attenuation of the auxin signaling pathway through down-regulation of auxin response factors (PpARF1), auxin-responsive genes (PpAUX/IAA1, PpSAUR1 and PpGH3–1), and auxin receptor proteins (PpTIR1) expressions. Our results suggested 1-MCP treatment improved chilling tolerance by regulating IAA biosynthesis, auxin signaling transduction and cell wall degradation, and provided new insight into the mechanisms of 1-MCP-induced cold resistance in postharvest peach fruit.

Effect of the pectin contents and nanostructure on the stem straightness of two Paeonia lactiflora cultivars.

Herbaceous peony (Paeonia lactiflora Pall.) is an ancient ornamental crop and, in recent decades, an emerging popular cut flower. Straight stems are a vital criterion for cut herbaceous peony selection, while many cultivars bend as the plant develops. Pectin helps maintain the mechanical strength of the cell wall. However, little is known about its role in the stem bending of herbaceous peony. Two herbaceous peony cultivars with contrasting stem morphologies ('Dong Fang Shao Nv', upright; 'Lan Tian Piao Xiang', bending gradually) at five developmental stages were used as materials to investigate the effects of pectin content and nanostructure on straightness using the carbazole colorimetric method and atomic force microscopy observations. The contents of water-soluble pectin (WSP), CDTA-soluble pectin (CSP), and sodium carbonate-soluble pectin (SSP) differed significantly between the two cultivars, and the contents and angle of the flower and branch showed correlations. For the pectin nanostructure, WSP showed agglomerates and long chains, with a higher proportion of broad agglomerates at the later stages of the bending cultivar than the upright cultivar. CSP showed branched chains, and the proportion of broad chains was higher in the upright cultivar at later stages, while CSP shape changed from agglomerates to chains in the bending cultivar. SSP mainly consisted of short linear main chains, and side chains in the upright stem were stacked, and the bent cultivar had more broad and short chains. It can be concluded that the contents, nanometric shape, and size of the three kinds of pectin are highly likely to affect herbaceous peony stem straightness. This study provides a theoretical basis for the role of pectin in the production and breeding of herbaceous peony cut flowers.

Transcriptome analysis reveals key metabolic pathways and gene expression involving in cell wall polysaccharides-disassembling and postharvest fruit softening in custard apple (Annona squamosa L.)

This study aimed to investigate the effect of custard apple cell wall polysaccharides-disassembling on postharvest fruit softening and to explore its key metabolic pathways and gene expression. Custard apple fruit was stored at 15 ± 0.5 °C for 12 days, it was found that the decreased significantly in fruit firmness, contents of Na2CO3-soluble pectin, hemicellulose and cellulose, and the increased significantly in water-soluble pectin and CDTA-soluble pectin. The activities of cell wall-degrading relevant enzymes in fruit were improved significantly during storage, including cellulase, polygalacturonase, pectin methyl esterase, neutral xylanase, β-galactosidase, and β-D-glucosidase. The RNA sequencing results revealed 41,545 nonredundant unigenes and 7571 differentially expressed genes (DEGs) in custard apple fruit samples. Functional annotation and DEGs data revealed cell wall degradation potentially involved in starch and sucrose metabolism, amino sugar and nucleotide sugar metabolism, galactose metabolism, pentose and glucuronate interconversions. Specifically, two EG and six β-Glc genes controlled the cellulose decomposition, and one β-xyl and one GATU genes involved in the degradation of hemicellulose, and two PME, one Pel, and four PG genes were the major regulators of pectin disassembling. These results provide a molecular foundation for explaining fruit softening and extending shelf life of custard apple.

Botrytis cinerea mediated cell wall degradation accelerates spike stalk browning in Munage grape.

Munage grape (Vitis vinifera L. cv. Munage.) is a unique cultivar in southern Xinjiang, China. Spike stalk browning in this species has becomes more common in recent years, negatively impacting the shelf life, and causing severe economic losses during storage. This study investigated the changes in metabolisms of cell wall by Botrytis cinerea infection in association with spike stalk browning. Morphological and physiological observations showed that preharvest B. cinerea infection accelerates the spike stalk browning during storage in Munage grapes by promoting cell wall degradation. Accordingly, the cell structures in infected spike stalk showed severe collapse, while the cell structures in uninfected spike stalk remained relatively complete. Furthermore, the contents of CDTA-soluble pectin (CSP), Na2 CO3 -soluble pectin (NSP), cellulose, and hemicellulose were reduced, while the water-soluble pectin (WSP) content was increased during infection. In addition, the activities of polygalacturonase (PG), pectin methylesterase (PME), beta-galactosidase (β-Gal), and cellulase (Cx) were highly promoted by B. cinerea. Correspondingly, the expression levels of VvPG were markedly upregulated after inoculation and played a major role in cell wall degradation. Additionally, the spike stalk inoculated by B. cinerea showed higher activities of PPO and POD, and content of total phenolics. These results contribute to elucidating the relationship between cell wall degradation induced by B. cinerea during spike stalk browning and provide a basis for future research on improving the ability of the host cell wall to resist degrading enzymes. PRACTICAL APPLICATIONS: Botrytis cinerea is the main fungal pathogen causing the gray mold of grapes. It usually enters the tissue early in crop development, has a long incubation period, and rapidly infects the tissue when the environment is favorable and the host physiology changes. Gray mold has been reported as one of the major postharvest diseases of grapes. However, there are relatively few reports on the pathways through which B. cinerea causes the browning of grape stalks. Controlling browning caused by B. cinerea may require clarification of the physiological and molecular mechanisms by which browning occurs. The elucidation of the role of B. cinerea in causing browning of grape stalks through the cell wall degradation pathway will help to provide scientific basis for further controlling browning, maintaining freshness of stalks, developing biological agents to prevent browning, improving grape quality, and extending storage period.

Salicylic acid treatment delays apricot (Prunus armeniaca L.) fruit softening by inhibiting ethylene biosynthesis and cell wall degradation

Apricots softening senescence is a complex metabolic network, and these metabolic pathways coordinate with each other to make aging irreversible. To identify and implement treatments to delay ripening senescence in apricots, the effects of salicylic acid (SA) treatment on ethylene biosynthesis and cell wall degradation were investigated during 35 days of storage at 4 °C and 90%-95% relative humidity. In contrast with control, SA treatment suppressed ethylene production due to inhibited ACC synthase (ACS) and ACC oxidase (ACO) activities and reduced 1-aminocyclopropane-1-carboxylic acid (ACC) content. Furthermore, the decreases in fruit firmness, contents of CDTA-soluble pectin (CSP), Na2CO3-soluble pectin (NSP), hemicellulose as well as cellulose, and the increase in water-soluble pectin (WSP) of the apricots could be delayed by SA treatment. Enzyme activities of cellulase (EC 3.2.1.4), β-glucosidase (EC 3.2.1.21), polygalacturonase (PG; EC 3.2.1.15), pectin methylesterase (PME; EC 3.1.1.11) as well as PaPG1 and PaPME1 gene expressions were suppressed strongly by SA treatment and these two genes were closely correlated with fruit softening. In addition, transmission electron microscopy (TEM) images demonstrated that the softening process of SA-treated apricots could be delayed efficiently and preventing structural breakdown. These results suggest that cell wall degrading enzyme activities are regulated by ethylene, and SA treatment mitigated apricots softening by inhibiting ethylene biosynthesis and decreasing cell degrading enzyme activities.

Physicochemical and structural properties of three pectin fractions from muskmelon (Cucumis melo) and their correlation with juice cloud stability

Pectin is one of the crucial endogenous components in cloudy juice and easily affects cloud stability due to its stabilizing property. To obtain improved cloud stability, the physicochemical and structural characteristics of pectin fractions from muskmelon and their correlation with juice cloud stability were investigated. In this study, a water-soluble pectin fraction, a trans-cyclohexane-1,2-diaminetetraacetic acid (CDTA)-soluble pectin fraction, and a sodium carbonate-soluble pectin fraction were sequentially extracted from the whole muskmelon fruits. All pectin fractions were classified as low-methoxy pectin and contained 3.06–8.26% protein. Measurements of the monosaccharide compositions and microstructure showed that CDTA-soluble pectin and water-soluble pectin consisted of aggregates of linear homogalacturonan, whereas sodium carbonate-soluble pectin was more highly branched. Analysis of Fourier transform infrared and nuclear magnetic resonance spectroscopy revealed observable differences between the chemical structures of the three pectin fractions. Thermogravimetric analysis indicated sodium carbonate-soluble pectin had the highest thermal stability than other pectin. Of all pectin fractions, CDTA-soluble pectin had the highest molecular weight, which resulted in the highest apparent viscosity. Moreover, the principal component analysis showed that CDTA-soluble pectin played an important role in cloud stability. This study will provide valuable information for the melon juice industry with regard to the utilization of pectin to improve cloud stability.

The Mechanism of Extraction of Peanut Protein and Oil Bodies by Enzymatic Hydrolysis of the Cell Wall.

Degradation of the peanut cell wall is a critical step in the aqueous enzymatic extraction process to extract proteins and oil bodies. Viscozyme® L, a compound cell wall degrading enzyme, has been applied as an alternative to protease in the process of aqueous enzymatic extraction, but the mechanism of cell wall enzymolysis remains unclear. The present study aims to investigate the changes in cellulose, hemicellulose, and pectin content of the peanut cell wall hydrolyzed by Viscozyme® L. The degree to which the main components of the peanut cell wall, such as trans-1, 2-cyclohexanediamine-N,N,N',N'-acetic acid-soluble pectin (CDTA-soluble pectin), Na2CO3-soluble pectin, cellulose, and hemicellulose, are degraded is closely related to the extraction of oil bodies and peanut protein at different solid-liquid ratio of powered peanut seed in distilled water, enzyme concentration, enzyme hydrolysis temperature, and enzyme hydrolysis time. The key sites of Viscozyme® L activity on cell wall polysaccharides were explored by comparing the changes in chemical bonds under different extraction conditions using Fourier-transform infrared spectroscopy (FT-IR) absorption bands and principal component analysis (PCA). Viscozyme® L acted on the C-O stretching, C-C stretching, and CH2 symmetrical bending of cellulose, the C-O stretching and O-C-O asymmetrical bending of hemicellulose, and the C-O stretching and C-C stretching of pectin.

Effects of nitric oxide fumigation treatment on retarding cell wall degradation and delaying softening of winter jujube (Ziziphus jujuba Mill. cv. Dongzao) fruit during storage

Winter jujube (Ziziphus jujuba Mill. cv. Dongzao) fruit were fumigated with 20 μL L−1 of nitric oxide (NO) for 3 h and then stored at 0 ± 1 ºC with 90–95 % relative humidity for 75 d. The effects of NO fumigation on changes in fruit firmness, activities of cell wall degrading enzymes, the compositions of the cell walls, as well as the cell wall ultrastructure in the winter jujube fruit were investigated during storage. The results showed that the decline in fruit firmness, contents of CDTA-soluble pectin (CSP), Na2CO3-soluble pectin (SSP), hemicellulose, and cellulose, as well as the increase in water-soluble pectin (WSP) of the winter jujube fruit could be delayed by NO treatment relative to the control. NO treatment also suppressed the activities of pectin methylesterase (PME; EC 3.1.1.11), polygalacturonase (PG; EC 3.2.1.15), β-galactosidase (β-Gal; EC 3.2.1.23) and cellulase (EC 3.2.1.4) during storage. Furthermore, ultrastructural observations revealed that NO treatment delayed the disruption of cell wall structure of the winter jujube fruit. These results indicated that retarding the disassembly of cell walls polysaccharides via inhibition of an array of cell wall degrading enzymes activities, which in turn would help maintain the intactness of the cell walls, might be one possible mechanism by which NO treatment can help prevent softening of the winter jujube fruit.

Increased firmness and modified cell wall composition by ethylene were reversed by the ethylene inhibitor 1-methylcyclopropene (1-MCP) in the non-climacteric olives harvested at dark green stage – Possible implementation of ethylene for olive quality

This study aimed to investigate the firmness retention by ethylene treatment in olive fruit, as observed earlier. Ethylene concentrations up to 1000 μL L−1 were applied to dark green ‘Konservolia’ olives harvested shortly before the green maturation and exposed to 20 °C for up to 9 d. Surprisingly, the results indicated a tendency to fruit firmness increases in concentration-dependent manner in a non-climacteric fruit. The highest concentration increased the firmness within 12 h by approximately 1.35-fold, but transiently for approximately up to 5 d; all ethylene inhibitors tested, either of synthesis (ethoxyvinyl glycine or AVG), or perception (1 -methyl-cyclopropene or 1-MCP, and silver nitrate) prevented the firmness increase. Texture was evaluated by firmness and changes in lignin, cellulose (CL), total pectins (TPC), water soluble pectins (WSP) and total non-cellulosic sugars (total sugars) concentrations, and in pectin esterification degree (DE) in the alcohol insoluble residue (AIR) of ‘Konservolia’ fruit pericarp during 1.5-d, 5-d and 10-d treatments with 1000 μL L-1 ethylene at 20 °C. Pectins in AIR were also extracted sequentially with cyclohexane-trans-1,2-diaminetetra-acetate (CDTA), Na2CO3, 1 M and 4 M KOH. The results showed that on day 1.5, the increased firmness was consistent with increased CL (crystalline formation, as observed by microscopy), total sugars and DE levels, but reduced WSP, whereas softening reversed the changes and lowered TPC and CDTA-soluble pectins in all fruit on day 10. However, on day 5 ethylene-treated olives exhibited a transitional phase during softening, characterized by retention of high TPC concentration and energy demand, as indicated by elevated respiration rates. The inhibitor 1-MCP, applied before ethylene, did inhibit the responses to ethylene treatment. Ethylene firming effect and the respective cell wall changes in olives are demonstrated for first time. The experiments could be used for research on perception and transcription responses to ethylene in olive, a non-climacteric fruit. In practice, high ethylene concentrations could also be beneficial for firmness increase and/or short storage of dark green olives.

Relationship between texture and cell-wall components of safou (&lt;i&gt;Dacryodes edulis&lt;/i&gt; (G. Don) H.J. Lam) fruits at different storage conditions

Objective: The objective of this study was to determine the relationship between texture and cell wall component of safou (Dacryodes edulis (G Don) HJ Lam) at different storage conditions during the safou softening.Methodology and results: Using a General Linear Model (GLM), statgraphic software plus v. 5. 0 and XLstat 2007software, the relationship between texture and cell wall component of safou at different storage conditions was evaluated. At different stages of ripeness, safou were picked and stored in different conditions including: cultivar, picking mode, packaging mode and temperature. For each condition, texture, water loss, alcoholinsoluble CDTA- soluble pectins and neutral sugar level and methoxylation degree were measured.The results showed that the temperature and method of storage and theirs interaction influenced significantly the texture of the safou during storage. Softening and dehydration through transpiration are the two processes that changed the safou texture at high temperature (28°C and 36°C). The cultivar and the maturity stage also influenced significantly the texture. The correlation between texture and cell-wall component including alcohol insoluble solids, CDTA soluble pectin extracts, rhamnose and arabinose were very high. MIA (Materiel Insoluble in Alcohol) content increased and galacturonic acid content of CDTA Soluble Pectin extracts decreased, depending on the maturity level of safou: the degradation of homogalacturonans of pectins during the safou softening.Conclusion and application of results: the degradation of homogalacturonans of safou pectins had an impact on their texture. Therefore, for their postharvest shelf life, safou must be stored at low temperature (18°C) with or without packing.Keywords: Safou, texture, pectins, softening, Dacryodes edulis

Boron Deficiency in Trifoliate Orange Induces Changes in Pectin Composition and Architecture of Components in Root Cell Walls.

Boron (B) is a micronutrient indispensable for citrus and B deficiency causes a considerable loss of productivity and quality in China. However, studies on pectin composition and architecture of cell wall components in trifoliate orange roots under B deficiency condition are not sufficient. In this study, we investigated the alteration in pectin characteristics and the architecture of cell wall components in trifoliate orange [Poncirus trifoliata (L.) Raf.] roots under B starvation. The results showed that B-deficient roots resulted in a significant enlargement of root tips and an obvious decrease in cell wall B and uronic acid content in Na2CO3-soluble pectin compared with B-adequate roots. Meanwhile, they showed a decrease of 2-keto-3-deoxyoctanoic acid in CDTA-soluble and Na2CO3-soluble pectin in cell walls, while the degree of methylation (DM) of CDTA-soluble pectin was significantly increased under B deficiency. Transmission electron microscope (TEM) micrographs of B deficient plants showed a distinct thickening of the cell walls, with the thickness 1.82 times greater than that of control plant roots. The results from Fourier-transform infrared spectroscopy (FTIR) showed that B deficiency changed the mode of hydrogen bonding between protein and carbohydrates (cellulose and hemicellulose). The FTIR spectra exhibited a destroyed protein structure and accumulation of wax and cellulose in the cell walls under B starvation. The 13C nuclear magnetic resonance (13C-NMR) spectra showed that B starvation changed the organic carbon structure of cell walls, and enhanced the contents of amino acid, cellulose, phenols, and lignin in the cell wall. The results reveal that the swelling and weakened structural integrity of cell walls, which induced by alteration on the network of pectin and cell wall components and structure in B-deficient roots, could be a major cause of occurrence of the rapid interruption of growth and significantly enlarged root tips in trifoliate orange roots under B-insufficient condition.

Changes of reactive oxygen species and scavenging enzymes of persimmon fruit treated with CO2 deastringency and the effect of hydroxyl radicals on breakdown of cell wall polysaccharides in vitro

Few studies have examined the non-enzymatic disassembly of cell walls in persimmon fruits. The objective of the study was to investigate the changes in the levels of reactive oxygen species and in the activity of antioxidative enzymes and, to evaluate the effect of OH on the in vitro breakdown of cell wall polysaccharides of persimmon fruit at different ripening stages. After harvest, persimmon (Diospyros kaki, ‘Mopan’) fruits were treated with 95% CO2 at room temperature, and the results showed that fruit firmness rapidly decreased and the respiratory and ethylene release rates increased. At the same time, hydroxyl radicals (OH) and O2− rapidly accumulated, and the activities of related antioxidant enzymes such as dismutase peroxidase, catalase and peroxidase superoxide, also changed. The effects of OH induced by the Fenton reaction on the cell wall materials in vitro were investigated; the water soluble pectin and CDTA-soluble pectin contents increased, and Na2CO3-soluble pectin content decreased. Due to the increasing levels of reactive oxygen species, especially OH, during persimmon fruit softening, and the in vitro effect of OH on the scission of cell wall polysaccharides, we postulated that OH may be involved in persimmon fruit softening.

Effect of β-aminobutyric acid on cell wall modification and senescence in sweet cherry during storage at 20 °C

The effects of postharvest β-aminobutyric acid (BABA) treatment on fruit firmness, pectin degrading enzymes, cell wall constituents and microstructural alterations of pericarp in sweet cherry fruit were investigated. BABA significantly delayed the decline of fruit firmness and inhibited the increase of membrane permeability and the accumulation of malondialdehyde in cherries. The BABA-treated fruit exhibited significantly higher contents of water-soluble pectin, CDTA-soluble pectin, Na2CO3-soluble pectin, total pectin, cellulose and hemicellulose than the control during storage. Activities of pectin degrading enzymes including polygalacturonase and pectinmethylesterase were markedly reduced by BABA treatment. Observations by scanning electron microscopy showed BABA maintained smooth cuticle and integrated structure of subepidermal cell in sweet cherry. These results suggest that the delay in fruit senescence by BABA may be due to depressed membrane permeability and malondialdehyde content, reduced activities of polygalacturonase and pectinmethylesterase, enhanced cell wall polysaccharides content, and integrated subepidermal cell structure in sweet cherry.

Modification of pectin and hemicellulose polysaccharides in relation to aril breakdown of harvested longan fruit.

To investigate the modification of cell wall polysaccharides in relation to aril breakdown in harvested longan fruit, three pectin fractions (WSP, water soluble pectin; CSP, CDTA-soluble pectin; ASP, alkali soluble pectin) and one hemicellulose fraction (4 M KOH-SHC, 4 M KOH-soluble hemicellulose) were extracted, and their contents, monosaccharide compositions and molecular weights were evaluated. As aril breakdown intensified, CSP content increased while ASP and 4 M KOH-SHC contents decreased, suggesting the solubilization and conversion of cell wall components. Furthermore, the molar percentage of arabinose (Ara), as the main component of the side-chains, decreased largely in CSP and ASP while that of rhamnose (Rha), as branch point for the attachment of neutral sugar side chains, increased during aril breakdown. Analysis of (Ara + Gal)/Rha ratio showed that the depolymerization of CSP and ASP happened predominantly in side-chains formed of Ara residues. For 4 M KOH-SHC, more backbones were depolymerized during aril breakdown. Moreover, it was found that the molecular weights of CSP, ASP and 4 M KOH-SHC polysaccharides tended to decrease as aril breakdown intensified. These results suggest that both enhanced depolymerization and structural modifications of polysaccharides in the CSP, ASP and 4 M KOH-SHC fractions might be responsible for aril breakdown of harvested longan fruit.