Chelator-soluble Pectin Research Articles

Changes in pericarp morphology, physiology and cell wall composition account for flesh firmness during the ripening of blackberry (Rubus spp.) fruit

Fruit flesh firmness plays a critical role in controlling blackberry (Rubus spp.) postharvest shelf life. This work aimed to identify the underlying characteristics in pericarp morphology, cell wall hydrolase activity and cell wall composition that account for flesh firmness in soft-fruited ‘Boysen’ and firm-fruited ‘Arapaho’ cultivars that have a similar ripening time of 39 days after flowering (DAF). The fruit firmness of both fruits decreased noticeably at the onset of color change, and this decrease hastened from 33 DAF to ripening despite considerable differences in their temporal changes. The evaluation of pericarp cellular morphology revealed that the disassembly of the cell wall in both fruits was likely initiated at 33 DAF, followed by extreme degradation at 39 DAF. Cell wall hydrolase activity assays indicated that increases in polygalacturonase (PG) and cellulase activity also dramatically occurred in the late softening stages of both fruits. Notably, appreciably higher levels of cellulase, and significant increases in pectin methylesterase (PME), α-L-arabinofuranosidase (α-L-Af) and xyloglucan endotransglycosylase (XET) were only detected in the late ripening stages of ‘Boysen’. In terms of cell wall components, the levels of cell wall material (CWM), cellulose and hemicellulose declined similarly during ripening in both fruits. Comparatively, lower levels of CWM, chelator soluble pectin (CSP), sodium carbonate soluble pectin (SSP), and hemicellulose as well as higher levels of water soluble pectin (WSP) were found in ‘Boysen’ than those in ‘Arapaho’ during maturation and ripening. Overall, the loss of fruit firmness during ripening in blackberry fruit is correlated closely with biochemical changes in cell wall fractions that involve hydrolytic processes, resulting in the breakdown of cell-wall polymers. The low firmness of ‘Boysen’, as determined by cell wall degradation, could be of particular relevance to the function of cell wall degrading enzymes and to the more drastic degradation of cell wall components than that in the firm cv. ‘Arapaho’.

New evidence on pectin-related instantaneous pressure softening mechanism of asparagus lettuce under high pressure processing.

Evidence on mechanism of instantaneous pressure softening of asparagus lettuce under high pressure processing was explored with respect to pectin methylesterase activity, degree of methylation of pectin, degree of methylation patterns of pectin fractions, and pectin distribution in cell wall matrix. Instantaneous pressure softening was observed at 300 MPa, while texture recovery was obtained at 500 MPa. Pectin methylesterase activity was not significantly affected at 100 and 300 MPa, but dramatically activated at 500 MPa (p < 0.05). Correspondingly, the degree of methylation of pectin decreased as pressure rose. Results of in situ immuno-dot blotting and immunolabeling based on specific bindings of antipectin antibodies showed a significant reduction of chelator-soluble pectin at 300 MPa, in contrast to a remarkable increase at 500 MPa. High pressure processing-induced demethoxylation was further verified by the enhanced fluorescence intensity of LM19 (an antihomogalacturonan antibody specifically binds to nonmethoxylated pectin) immunolabeled pectin, which was mainly located in tricellular junctions at 300 MPa, but covered the full cell surface at 500 MPa. In conclusion, instantaneous pressure softening of asparagus lettuce is strongly associated with loss of chelator-soluble pectin at 300 MPa.

Distribution of arabinogalactan proteins and pectins in the cells of apple (Malus × domestica) fruit during post-harvest storage.

Changes in the arrangement of cell wall components determine cell wall properties (integrity, stiffness), thereby affecting the macro-scale properties of fruits, which are important for consumers and industry. Arabinogalactan proteins (AGPs) are ubiquitous components of the plant cell, in which they have various functions. Currently, AGPs are considered to be one of the less well-known, enigmatic proteoglycans, a consequence of their heterogeneous structure and unclear mechanism of activity. An immunocytochemical study was conducted to elucidate the distribution of AGPs and pectic polysaccharides contained in apple (Malus × domestica) fruit during senescence. De-esterified homogalacturonan (LM19), methyl-esterified homogalacturonan (LM20), processed arabinan (LM16) and three AGP epitopes (JIM13, JIM15, MAC207) were identified in the fruit at three stages: fresh fruit, and fruit at 1 and 3 months of post-harvest storage. Microscopy revealed spatio-temporal changes in the localization of all examined epitopes. Changes of fruit cell wall assembly and its degradation were confirmed by determination of the galacturonic acid content in the WSP (water soluble pectins), CSP (chelator soluble pectins) and DASP (dilute alkali soluble pectins) fractions. The results revealed dependencies between AGPs, arabinan and homogalacturonan distribution in apple fruit, which are correlated with changes in microstructure during senescence. We propose that AGPs are involved in establishment of the cell wall - plasma membrane continuum.

Evaluation of pectin nanostructure by atomic force microscopy in blanched carrot

Low-temperature blanching (LTB) is a very attractive method for preserving the texture of fresh vegetables; however, the molecular basis of this treatment remains to be elucidated. The mechanism of textural change in carrots by LTB was investigated. Carrot samples were treated using three kinds of blanching: high-temperature blanching (HTB), LTB, and LTB followed by HTB. Fresh and treated samples were evaluated conventionally for firmness, galacturonic acid content, and the activity of pectin methylesterase. In addition, Raman microscopy was also used to describe the pectin distributions in the samples. However, the Raman maps did not show obvious differences among the samples, but they coincided with the results of galacturonic acid content. Furthermore, the nanostructures of water-soluble pectin (WSP), chelator-soluble pectin (CSP), and diluted alkali-soluble pectin (DASP) fractions were observed by atomic force microscopy. The median length of CSP molecules was shortened from 44.76 nm to 12.57 nm by HTB. On the other hand, LTB induced elongation of CSP molecules (median length: 58.12 nm) and maintaining ability of DASP to form a regular network on mica.

Effects of Calcium Concentration in Potato Tuber Cells on the Formation of Cross-Links between Pectin Molecules by Ca2+

The formation of cross-links between pectin molecules via Ca2+ in the potato tuber cell wall is a determinant factor on processing properties of potato and the quality of its products such as French fries. Thus, in this study, potato tubers varying significantly in their calcium concentrations were analyzed to investigate whether an increased absorption of calcium by a potato tuber led to an increase in the calcium concentration in the cell wall and how the calcium concentration in the cell wall influenced on the formation of cross-links between pectin molecules via Ca2+. Correlation analysis revealed that calcium absorbed by a potato tuber was bound to the cell wall as a water insoluble form 99 days after planting or later. Furthermore, with an increase in the calcium concentration in the cell wall, the content of chelator soluble pectin increased throughout tuber bulking and maturation stages. However, the degree of methylation was not a limiting factor in the formation of cross-links between pectin chains via Ca2+. Atomic force microscopy images of parenchyma cell walls prepared from mature potato tubers indicated an increase in the amount of calcium cross-linked pectin molecules with an increase in the calcium concentration in the cell wall. The present study demonstrated that the calcium concentration of the cell wall of potato tubers significantly affected the formation of cross-linkages between pectin molecules and, consequently, contributed to an enhanced formation of pectin-calcium networks in the cell wall.

Boron Supply Enhances Aluminum Tolerance in Root Border Cells of Pea (Pisum sativum) by Interacting with Cell Wall Pectins.

Aluminum (Al) toxicity is the primary factor limiting crop growth in acidic soils. Boron (B) alleviates Al toxicity in plants, which is mainly considered to be due to the formation of Rhamnogalacturonan II-B (RGII-B) complexes, which helps to stabilize the cytoskeleton. It is unclear yet whether this is due to the increasing of net negative charges and/or further mechanisms. Kinetics of Al accumulation and adsorption were investigated using entire cells, cell wall and pectin of root border cells (RBCs) of pea (Pisum sativum), to reveal the mechanism of B in interacting with alkali-soluble and chelator-soluble pectin for an increased Al tolerance in RBCs. The results show that B could rescue RBCs from Al-induced cell death by accumulating more Al in the cell wall, predominately in alkali-soluble pectin. Boron also promotes Al3+ adsorption and inhibits Al3+ desorption from alkali-soluble pectin. Thus, more Al3+ is immobilized within the alkali-soluble pectin fraction and less in the chelator-soluble pectin, rendering Al3+ less mobile. Boron induces an increase of RG-II (KDO,2-keto-3-deoxyoctonic acid) content for forming more borate-RGII complexes, and the decrease of pectin methyl-esterification, thus creates more negative charges to immobilize Al3+ in cell wall pectin. The study provides evidence that abundant B supply enhances the immobilization of Al in alkali-soluble pectin, thus most likely reducing the entry of Al3+ into the symplast from the surroundings.

Dietary fiber and cell wall polysaccharides from plum (Prunus domestica L.) fruit, juice and pomace: Comparison of composition and functional properties for three plum varieties

The aim of the present work was to characterize the pectins present in plum fruit, juice, and pomace for three plum varieties, “Promis,” “Najbolja,” and “Dąbrowicka” (all belonging to the species Prunus domestica L.). The content of dietary fiber in the pomace was 5 to 9 times higher than that in the fruit. In turn, the content of soluble fibers and readily soluble pectins (water and chelator soluble pectins) was markedly lower as compared to the fruit, and their hydrodynamic volume was decreased, especially in the case of water soluble pectins. As a result, the hydration capacity of AIS from the pomace was half of that of AIS from the fruit, but its levels were still high enough for it to be used as an ingredient in food products (WBC>5.5g/g). Thus, plum pomace could be an efficient source of functional fibers.

Hot Air Treatment Improved the Chilling Resistance of Loquat Fruit under Cold Storage

Absract Hot air treatment at 38C for 36 h significantly improved the chilling resistance of loquat during 4C storage for 28 days, appeared as higher extractable juice, lower firmness, internal browning and decay development. This treatment reduced hydrogen peroxide level by improving superoxide dismutase, ascorbate peroxidase, glutathione reductase and catalase activities, then maintained higher unsaturated/saturated fatty acid ratio and lower permeability of membrane at the end of storage. It also reduced phenylalanine ammonia lyase, peroxidase and polyphenol oxidase activities, and total phenolic content to control internal browning and lignin synthesis; the enhanced antioxidant enzyme activities also contribute to control them. Meanwhile, heat-treated fruits showed significantly higher levels of water- and chelator-soluble pectins and lower Na2CO3-soluble pectin than controls at the later of storage. It was suggested that the improved chilling resistance by heat treatment maybe mainly due to the enhanced scavenging capacity of oxygen species and solubilization of cell wall polysaccharides. Practical Applications Loquat fruit is very perishable because of microbial decay and mechanical damage after harvest. Low-temperature storage is an effective method to control pathogenic decay and preserve quality. However, loquat fruit are chilling-sensitive, and chilling injury limits the storage period and shelf-life. This work investigated the effects of hot air treatment on the chilling resistance of loquat fruit. It was found that heat treatment at 38C for 36 h can enhance the chilling resistance, reduce the chilling symptoms and maintain higher quality after storage at 4C for 28 days. The information obtained from this study suggested that this heat treatment may be a suitable method for the commercial application on loquat fruits.

High‐temperature conditioning induces chilling tolerance in mandarin fruit: a cell wall approach

High-temperature conditioning (3 days at 37 °C and 95% relative humidity), which protects 'Fortune' mandarins from chilling injury (CI), manifested as pitting in the outer part of the peel (flavedo), was applied prior to cold storage (2 °C) in order to investigate the involvement of cell wall composition in the chilling tolerance of mandarins. Both low-temperature storage and high-temperature conditioning barely modified the alcohol-insoluble substance (AIS) content or the degree of pectin esterification in the flavedo. Water-soluble pectins (WSP) were higher in heat-conditioned than in non-conditioned fruits at the onset of CI. In addition, the heat-conditioning treatment was able to increase chelator-soluble pectins (CSP) after short cold storage periods. Covalently bound polyuronides in alkali-soluble pectins (ASP) increased only in fruits with high incidence of CI. Cellulose and hemicellulose increased at 2 °C in both conditioned and non-conditioned fruits, indicating that these polysaccharides may be altered by low temperature but are not related to chilling-induced damage. High-temperature conditioning may reduce chilling-induced flavedo pitting in 'Fortune' mandarin fruit by maintaining normal levels of WSP and increasing putative sites for calcium bridge formation within the cell wall, but not by inducing changes in other matrix cell wall components.

Potential mechanisms associated with strawberry fruit firmness increases mediated by elevated pCO2

Postharvest treatment of strawberry fruit with an elevated pCO2 induces transient increases in the fruit firmness. The mechanism responsible for this firmness increase is not clearly understood. This study addressed the physiological responses of strawberry fruit to CO2 treatment to understand the factors to induce firmness increase. High CO2 treatment induced modification of pectic polymers, the decrease of water-soluble pectins (WSP) and increase of chelator-soluble pectins (CSP), which are the major factors for firmness increase. The shift of WSP to CSP is related with calcium binding to WSP. The calcium binding to wall polymers was induced without changes of PME activity and methoxy content of WSP and CSP. Our results suggested that fruit firmness increase of strawberry by postharvest CO2 treatment occurred primarily through pectin polymerization mediated by calcium.

GENETIC BACKGROUND OF QUALITY AND CELL WALL CHANGES IN FRESH-CUT MELONS

Fresh-cut melon is a growing and convenient segment ot melon products. Melon cultivars were not bred specifically for fresh-cut processing, and the genetic bases for fresh-cut quality are unknown. We examined the link between fresh-cut quality, cell wall changes, and genetics in three near-isogenic lines (NILs) of melon (Cucumis melo L.) and in a 'Piel de Sapo' (PS) cultivar during a 9-day storage period at 4°C. The three NILs differed in initial firmness and differences persisted throughout storage of fresh-cut melon. Juice efflux was negatively correlated with flesh firmness. The climacteric NIL SC3-5-1 was softer and had higher juice efflux than the remaining NILs of the parental line PS. Fresh-cut prepared from NILs SC7-2 and SC10-2 were firmer and generally released less juice than SC3-5-1 and PS. Chelator-soluble pectins of SC3-5-1 exhibited a marked molecular size downshift during a 6-day storage period in SC3-5-1, but no significant differences in molecular size distribution were observed in the other NILs. Apparently two different quantitative trait loci (QTL) with pleiotropic effect were affecting flesh firmness and juice efflux. One QTL located in the linkage group (LG) III increased pectin depolymerisation, which was probably associated with climacteric behavior. Another two QTLs in LG VII and X were associated with initial firmness levels.

Effect of 1-MCP and High $pCO_2$ Treatment on the Firmness and Pectin Changes in Peach(Prunus persica) Fruit During Shelf-life

In order to understand the effects of a single or combined trea tments of 1-MCP(1μL/L) and CO 2(100%) on the firmness of melting type peach fruit(cv. Chunjungdo), fruit were harvested at commercial maturity and examined physiological changes including flesh firmness during 10 days of shelf-life. Firmness loss of fruit was delayed by both single and combined treatments of 1-MCP and CO 2. The treatment of 1-MCP was more effective than CO2 treatment but no additive effective on firmness retention was found in the combined treatment. The upsurge of ethylene evolution occurred 5 days of shelf-life in air treated control but ethylene evolution gradually increased in fruit treated by 1-MCP and 1-MCP+CO2. The suppression of ethylene evolution seemed stronger in CO2 treatment. The respiration of fruit significantly inhibited up to 10 days except control where climacteric increase of respiration was found at 10 days of she lf-life. A molecular shift of pectic polymers(an increase of chelator soluble pectins and decrease of water soluble pectins) was induced by both 1-MCP and CO2 treatments. An increase of water soluble pectins was coincident with firmness loss. The delay of firmness loss seemed to be associated with the migration of calcium to wall matrix, especially pectins, resulting in the increase of wall bound calcium. The polygalacturonase activity was significantly reduced by 1-MCP alone 1 day after t reatment and increased to similar level of activity 5 days after treatment compared to other treatment except air treated control whereas pectin methylesterase activity seemed not to be affected by both 1-MCP and CO 2 treatments. Thus, the molecular shift of pectic polymers appeared not to be related with pectin methylesterase. Further study is required to clarify the softening mechanism associated with molecular shift of pectic polymers and the inter- or intra-cellular movement of calcium ions induced by postharvest treatments of 1-MCP and CO2.

Co-products of black-currant and apple juice production: Hydration properties and polysaccharide composition

The sugar composition in cell walls of apple and black currant pomaces was investigated with or without solvent extraction. Extraction of polyphenols by solvents changed the sugar composition of cell walls by increasing the alcohol insoluble solids (AIS) contents and increasing glucose content. Water binding capacity was increased by the ethanol extractions, but decreased again after acetone treatments. The enzyme treatments used for juice extraction increased the swelling capacity but decreased the water binding capacity, probably by loosening the cell wall structure. They resulted in decreased degrees of methylation. Pectin extractability of black currant pomaces differed between the commercial pomace (higher Water Soluble Pectins fraction and Chelator Soluble Pectins fraction), and the experimental pomaces (higher Diluted Alkali Soluble Pectins fraction).

Enzymatic activity and substrate specificity of recombinant tomato β-galactosidases 4 and 5

The open reading frames of tomato beta-galactosidase (TBG) 4 and 5 cDNAs were expressed in yeast, and the enzymes properties and substrate specificities were investigated. The two enzymes had peak activities between pH 4-4.5 and 37-45 degrees C. TBG4 specifically hydrolyzed beta-(1-->4) and 4-linked galactooligosaccharides. TBG5 had a strong preference to hydrolyze beta-(1-->3) and beta-(1-->6)-linked galactooligosaccharides. Exo-beta-galactanase activity of the TBG enzymes was measured by determining the release of galactosyl residues from native tomato cell wall fractions throughout fruit development and ripening. Both TBGs released galactose from all of the fractions and stages tested. TBG4 activity was highest using chelator soluble pectin and alkali soluble pectin at the turning stage of ripening. Using aminopyrene trisulfonate labeled substrates, TBG4 was the only enzyme with strong exo-beta-(1-->4)-galactanase activity on 5 mer or greater galactans. TBG4 and TBG5 were both able to degrade galactosylated rhamnogalacturonan. Neither enzyme was able to degrade galactosylated xyloglucan.

Cell wall metabolism during durian fruit dehiscence

Changes in cell wall composition and enzyme activities were studied during durian fruit dehiscence. Water-soluble pectin concentrations remained constant for 2 days in both the husk and the dehiscence zone (DZ), and then increased in the DZ toward the end of storage. Chelator-soluble pectin was higher in the DZ at harvest and throughout storage. This pectin fraction increased steadily in both tissues. Na 2CO 3-soluble pectin content was about the same in the husk and the DZ, but slightly decreased during the dehiscence process. Hemicellulose (1 and 4 M KOH-soluble fractions) slowly decreased in the husk and the DZ during storage. The molecular size distribution of the three pectin fractions shifted from a larger molecular size to a smaller size, during durian dehiscence. The DZ was found to contain smaller pectin molecules than the husk. There was no change in molecular size in the 1 M KOH fraction and only a minor change toward the smaller molecular size in the 4 M KOH fraction during the later period of durian dehiscence. Pectin methyl esterase activity, both in the husk and in the DZ, was the same at the beginning of storage. However, differences were observed by the time storage had ended. Polygalacturonase activity slowly increased in both tissues during 8 days of storage, with the activity always being higher in the DZ than in the husk, especially at late dehiscence. β-1,4-Endoglucanase activity increased more in the DZ than in the husk during the dehiscence process. β-Galactosidase activity increased during the first half of fruit ripening, and then declined. The results suggested that the durian dehiscence process mainly involved degradation of chelator-soluble pectin by polygalacturonase.

Non‐enzymatic Depolymerization of Carrot Pectin: Toward a Better Understanding of Carrot Texture During Thermal Processing

ABSTRACT Pretreated carrot discs were thermally processed (90 °C to 110 °C) in closed containers and the resulting textural characteristics were analyzed. The pretreatment conditions used include conventional high‐temperature blanching (90 °C, 4 min), low‐temperature blanching (LTB = 60 °C, 40 min), LTB combined with 0.5% calcium chloride soaking, LTB combined with 2% sodium chloride soaking, high pressure pretreatment (HP = 400 MPa, 60 °C, 15 min), HP combined with 0.5% calcium chloride soaking, and control (non‐pretreated sample). Alcohol insoluble residues (AIR) from the pretreated carrot discs were characterized in terms of degree of methoxylation (DM). The AIR samples were further subjected to fractionation into water‐soluble pectin (WSP), chelator‐soluble pectin (CSP), and sodium carbonate‐soluble pectin (NSP). Heat depolymerization patterns and β‐elimination kinetics were investigated on the different pectin fractions. Thermal texture degradation was strongly influenced by the pretreatment condition used and the processing temperature during subsequent thermal treatment. Pretreatment conditions that showed a significant reduction in DM exhibited decreased WSP content, reduced β‐elimination, and consequently superior textural characteristics. β‐elimination was markedly pronounced in the highly methoxylated WSP fractions. CSP and NSP fractions were insensitive to β‐elimination. A strong correlation (r&gt; 0.95) between thermal texture loss of carrots and β‐elimination kinetics exists. Overall, the benefits of controlled pectinmethylesterase activity in carrot processing were pointed out.

Biochemical and immunohistochemical analysis of pectic polysaccharides in the cell walls of Arabidopsis mutant QUASIMODO 1 suspension-cultured cells: implications for cell adhesion

Mutation in the Arabidopsis thaliana QUASIMODO 1 gene (QUA1), which encodes a putative glycosyltransferase, reduces cell wall pectin content and cell adhesion. Suspension-cultured calli were generated from roots of wild-type (wt) and qua1-1 A. thaliana plants. The altered cell adhesion phenotype of the qua1-1 plant was also found with its suspension-cultured calli. Cell walls of both wt and qua1-1 calli were analysed by chemical, enzymatic and immunohistochemical techniques in order to assess the role of pectic polysaccharides in the mutant phenotype. Compared with the wt, qua1-1 calli cell walls contained more arabinose (23.6 versus 21.6 mol%), rhamnose (3.1 versus 2.7 mol%), and fucose (1.4 versus 1.2 mol%) and less uronic acid (24.2 versus 27.6 mol%), and they were less methyl-esterified (DM: 22.9% versus 30.3%). When sequential pectin extraction of calli cell walls was performed, qua1-1 water-soluble and chelator-soluble extracts contained more arabinose and less uronic acid than wt. Water-soluble pectins were less methyl-esterified in qua1-1 than in wt. Chelator-soluble pectins were more acetyl-esterified in qua1-1. Differences in the cell wall chemistry of wt and mutant calli were supported by a reduction in JIM7 labelling (methyl-esterified homogalacturonan) of the whole wall in small cells and particularly by a reduced labelling with 2F4 (calcium-associated homogalacturonan) in the middle lamella at tricellular junctions of large qua1-1 cells. Differences in the oligosaccharide profile obtained after endopolygalacturonase degradation of alkali extracts from qua1-1 and wt calli indicated variations in the structure of covalently bonded homogalacturonan. About 29% more extracellular polymers rich in pectins were recovered from the calli culture medium of qua1-1 compared with wt. These results show that perturbation of QUASIMODO 1-1 gene expression in calli resulted in alterations of homogalacturonan content and cell wall location. The consequences of these structural variations are discussed with regard to plant cell adhesion.

Deterioration of beit alpha and slicing cucumbers ( Cucumis sativus L.) during storage in ethylene or air: Responses to suppression of ethylene perception and parallels to natural senescence

‘Manar’ beit alpha and ‘Thunder’ and ‘Sweet Marketmore’ fresh-market slicing cucumber ( Cucumis sativus L.) fruit were harvested at an immature stage of development (commercial maturity) and subsequently exposed to either air or 1.0 μl l −1 1-methylcyclopropene (1-MCP) prior to storage in air or 10 μl l −1 ethylene at 15 °C. Fruit exposed to 10 μl l −1 ethylene exhibited rapid and acute cellular breakdown reminiscent of other members of the Cucurbitaceae exposed to ethylene. Symptoms were evident following as few as 4 d of ethylene exposure and included fruit softening, mesocarp watersoaking, epidermal sloughing and limited loss of epidermal green color. As one index of cellular deterioration, exposure of ‘Manar’ cucumber to ethylene induced a rapid and significant decline (40%) in total cell wall uronic acid (UA) content compared with losses of about 5–6% in fruit treated with 1-MCP prior to ethylene exposure or in fruit receiving only 1-MCP. Molecular mass downshifts in both water and chelator-soluble pectins (CSP) were markedly accelerated in fruit receiving only ethylene, becoming evident after only 4 d of exposure. In contrast, control fruit receiving neither 1-MCP nor ethylene showed greatly reduced rates of uronic acid loss and pectin depolymerization, with significant declines in molecular mass not being noted until after 16 d of storage at 15 °C. Prior treatment of cucumber fruit with 1-MCP delayed fruit deterioration and pectin depolymerization. Pectin depolymerization was also suppressed in 1-MCP-treated fruit receiving continuous ethylene exposure throughout storage and was substantially lower than rates of depolymerization noted for control fruit. Inhibition of ethylene responsiveness in the fresh-market slicing cucumbers ‘Thunder’ and ‘Sweet Marketmore’ revealed marked differences in cultivar response to the ethylene antagonist. During storage without supplemental ethylene, prior exposure to 1-MCP resulted in significant retention of firmness and surface color in ‘Sweet Marketmore’. In contrast, 1-MCP had minimal effects on these attributes in ‘Thunder’, largely due to higher firmness and color retention of the control fruit in general. Parallels between ethylene-induced deterioration and natural senescence of cucumber fruit are discussed.

A comparative study on wall degrading enzymes, pectin modifications and softening during ripening of selected tropical fruits

Cell wall modifying capacity and enzyme composition of rapid and slow-softening tropical fruits during ripening were investigated with respect to that of tomato, noted to contain significant endo-polygalacturonases (endo-PG; EC 3.2.1.15) activities. Besides PG, other enzymes selected to represent their pectin and/or hemicellulose modifying potentials were pectin methylesterase (EC 3.2.1.11), β-galactosidase (EC 3.2.1.23), and (1→4)-β-glucanase (EC 3.2.1.4). Time for 50% firmness loss was about 1.5 days for Beaumont guava ( Psidium guajava L.), 3 days for tomato ( Lycopersicon esculentum Mill.), Mas banana ( Musa acuminata, AA group) and Eksotika papaya ( Carica papaya L.), 4.5 days for Harumanis mango ( Mangifera indica L.), and 20 and 24 days for B10 carambola ( Averrhoa carambola L.) and Kampuchea guava, respectively. Capacity to markedly modify cell walls as reflected by capability to impact increased pectin solubility and depolymerization of chelator-soluble pectin, and which varied markedly with the fruit types, may not necessarily be correlated with softening rate, neither was it dependent on the presence of any significant endo-PG activities. Extensive pectin modifications occurred in ripening tomato, mango and papaya. Beaumont guava and Mas banana, though softened rapidly, experienced much limited pectin degradation, seemingly unable to match the modifications that occur in the slow-softening carambola and Kampuchea guava. All fruits tested, except tomato, contained significant exo-PG (EC 3.2.1.67) activities, thus explaining that endo-PG might not be the determining factor of differential softening. All other enzymes, viz. pectin methylesterase, (1→4)-β-glucanase, and in particular, β-galactosidase seemed relevant and might contribute significantly to the observed variations in softening rate amongst the fruits.

Detection of Vacuum Infusion of Pectinmethylesterase in Strawberry by Activity Staining

ABSTRACT: Strawberry halves were infused with Valencia orange pectinmethylesterase (PME) under vacuum for 15 min at room temperature. Fruits were blotted onto pectin paper and stained for activity. Activity of PME‐infused fruit was about twice (0.36 unit/mL or 0.86 unit/mg protein) that of noninfused control (0.19 unit/mL) or water‐infused control (0.16 unit/mL). Instron firmness values were not significantly different (P± 0.05) between noninfused and PME‐infused fruit. Firmness of PME‐infused fruit was about twice that of water‐infused control. Water‐soluble pectin, chelator soluble pectin, alkaline soluble pectin, and total pectin ranged from 8.24 to 8.70, 3.24 to 4.56, 3.77 to 5.39, and 17.86 to 26.16 mg/100 mg alcohol insoluble solid (AIS), respectively, for all treatments.