Comparison of cell wall metabolism in the pulp of three cultivars of ‘Nanfeng’ tangerine differing in mastication trait

BACKGROUND: Like sweet orange (Citrus sinensis), tangerine (Citrus reticulata) is another citrus crop grown widely throughout the world. However, whether it shares a common mechanism with sweet orange in forming a given mastication trait is still unclear. In this study, three ‘Nanfeng’ tangerine cultivars, ‘Yangxiao‐26’ (‘YX‐26’) with inferior mastication trait, elite ‘YX‐26’ with moderate mastication trait and ‘Miguang’ (‘MG’) with superior mastication trait, were selected to investigate the formation mechanism of mastication trait. RESULTS: ‘MG’ had the lowest contents of total pectin, protopectin and lignin and the highest gene expression levels of citrus polygalacturonase (PG) and pectin methylesterase (PME) at the end of fruit ripening, whereas ‘YX‐26’ had the lowest water‐soluble pectin (WSP) content, the highest lignin content and the lowest PG and PME expression levels. The contents of cellulose and hemicellulose were similar among the three tangerines. CONCLUSION: The fruit mastication trait of C. reticulata was determined by the proportions of WSP and protopectin as well as lignin content, not by cellulose and hemicellulose contents. Pectin content could be a major contribution to the feeling of mastication trait, while PG and PME exhibited an important role in forming a given mastication trait according to the present results as well as previous results for C. sinensis. Copyright © 2011 Society of Chemical Industry     

采前喷施水杨酸对红地球葡萄采后果实软化的影响

为探究采前喷施水杨酸(salicylic acid,SA)处理对红地球葡萄采后果实软化进程的影响,以红地球葡萄为材料,采前喷施1.0 mmol/L SA处理,采收预冷后在常温(22±1)℃贮藏,分析果实品质、原果胶(protopec-tin,PP)、纤维素、水溶性果胶(water soluble pectin,WSP)...     

Structural and chemical differences in the cell wall regions in relation to scale firmness of three onion (Allium cepa L.) selections at harvest and during storage

BACKGROUND: Firmness in vegetables is an important textural attribute affecting consumer attitudes toward freshness and quality. Firmness, structural carbohydrates, polygalacturonase (PG), and pectin methylesterase (PME) activity were measured in three onion (Allium cepa L.) lines at harvest and after 4, 8, and 12 weeks of storage. RESULTS: The high‐dry‐matter onion, MBL87‐WOPL, had the firmest bulbs at harvest and delayed softening during storage. MBL87‐WOPL had the thickest cell wall/middle lamella region, and highest levels of dry matter and total uronic acid. Furthermore, MBL87‐WOPL had the lowest levels of PG and PME activity during storage. Pegasus, a poor‐storing cultivar, had the softest bulbs at harvest, lowest levels of uronic acid, and thinnest cell wall/middle lamella. A good storing, moderately firm onion cultivar (MSU4535B) presented intermediate levels of firmness and total uronic acid content. Differences in uronic acid in water‐soluble pectin accounted for much of the difference in total uronic acid among lines. Cellulose concentrations were similar among all lines at harvest. In addition, cellulose concentrations decreased in all lines during storage. Transmission electron microscopy performed on bulbs at harvest and after 12 weeks of storage indicated that degradation of the middle lamella had occurred during storage, leading to cell separation. CONCLUSION: Our results suggest that differences in onion scale firmness at harvest may be due to differences in water‐soluble pectin uronic acid concentrations. Furthermore, the rate of bulb softening during storage at 6.6 °C was greater in onion lines with higher levels of PME and PG activity in storage. Copyright © 2008 Society of Chemical Industry     

茄子果实采后软化过程中细胞壁组分及其降解酶活性的变化

研究了细胞壁组分及其降解酶活性的变化与茄子果实采后软化的关系。结果表明,采后茄子果肉硬度随贮藏时间的延长而不断下降。贮藏期间果肉水溶性果胶(WSP)含量在贮藏前12天不断增加,之后快速下降,而共价结合型果胶(CSP)、半纤维素和纤维素等细胞壁组分含量持续减少。果肉果胶甲酯酶(PME)、多聚半乳糖醛酸酶(PG)和纤维素酶(CX)活性均呈先升高后下降趋势,分别在贮藏至第6、9、12天达到最大值;β-半乳糖苷酶(β-Gal)活性始终保持较高水平,且在整个贮藏期间活性变化不明显。相关性分析结果表明,CSP、半纤维素和纤维素的降解与采后茄子果实软化密切相关,PG和CX在茄子果实采后软化过程中起着重要的作用。     

细胞壁组分及酶活性与清见果实囊衣绵韧的相关性

以清见杂柑为研究材料,进行定点和定期的跟踪测定,探究清见果实囊衣中果胶类物质、纤维素、半纤维素、木质素含量和果胶甲酯酶、多聚半乳糖醛酸酶、纤维素酶活性在花后120～300 d的动态变化情况,及其与清见果实囊衣绵韧程度的相关性。结果表明：囊衣胞壁物质含量在成熟后期均有下降,多聚半乳糖醛酸酶和纤维素酶活性在后期处于上升趋势,果胶甲酯酶则相反;较高水平的水溶性果胶和低水平的木质素、纤维素、半纤维素有利于清见果实良好化渣性的形成;从花后210～300 d,细胞壁中多聚半乳糖醛酸酶、纤维素酶活性高低是决定囊衣质地绵韧程度的关键因子。     

Effect of edible coatings on enzymes,cell-membrane integrity,and cell-wall constituents in relation to brittleness and firmness of Huanghua pears (Pyrus pyrifolia Nakai,cv. Huanghua) during storage

To investigate the effects of edible coatings, such as shellac and Semperfresh™ (sucrose-polyester based coating) on the brittleness and firmness of Huanghua pears (Pyrus pyrifolia Nakai, cv. Huanghua), the changes in the cell-membrane permeability and cell-wall constituents, such as total pectin (TP), Na₂CO₃-soluble pectin (NSP), CDTA-soluble pectin (CSP), water-soluble pectin (WSP), hemicellulose and cellulose were periodically measured, for up to 60 days of cold storage (4 °C) after harvesting. The activities of peroxidase (POD), pectinesterase (PE), polygalacturonase (PG), and cellulose were also assayed. The data suggested that high POD activity and low activity of cell-wall-degrading enzymes, such as PE, PG, and cellulase in the coated pears were associated with a high integrity of the cell membrane and few changes in the cell-wall constituents, which contributed to high levels of brittleness and firmness in the pears during storage; further, the shellac coating provided a better effect than Semperfresh coating.     

Texture improvement of fermented minced pepper under vacuum impregnation with pectin methylesterase and CaCl2 during fermentation

Fermented minced pepper (FMP) usually suffers from the deterioration of texture quality during fermentation, which can affect sensory and consumer acceptance. In this study, vacuum impregnation (VI) with CaCl₂, pectin methylesterase (PME) and CaCl₂ and PME (PME + CaCl₂ + VI) were compared to improve the texture quality of FMP. FMP treated with PME + CaCl₂ + VI showed the relatively intact cells structure after fermentation. In that case, its firmness maintained high level, while water-soluble pectin (WSP) content was minimum after fermentation. Meanwhile, the molar ratio of most monosaccharides of WSP in PME + CaCl₂ + VI treated FMP decreased, while rhamnose (Rha) molar ratio significantly (p < 0.05) increased after fermentation. The high Rha content represents the stability of rhamnogalacturonan-I linear skeleton of WSP. The negative effect on molecular weight of WSP was delayed by PME + CaCl₂ + VI treatment, and its peak area and value increased after fermentation. Atomic force microscope images indicated that PME + CaCl₂ + VI treatment could retain the long chain and branch structures, and inhibit the degradation of WSP net-like structure at some extent. Hence, PME + CaCl₂ + VI treatment was effective to improve the texture of FMP and inhibit the solubilisation of WSP via the formation of cross-linked pectin chains between Ca²⁺ and demethylesterified pectin.     

Pectic polysaccharides during ripening of mango (Mangifera indica L)

The content of pectin decreased from 2.0 to 0.7% fresh weight (FW) and there was a concomitant increase in free galacturonic acid from 36 to 168 mg% FW during ripening of mango. Ion exchange chromatography on DEAE/cellulose resolved the pectic fraction into seven distinct peaks, with all of them showing a drastic decrease in pectin content and molecular weight as fruit ripening progressed, which indicated significant depolymerisation in vivo. Fraction I appeared to be an arabinogalactan‐type polymer, while fractions II and III were heterogalacturonans containing more than 60% galacturonic acid. Hydrolases implicated in pectin depolymerisation were polygalacturonase (PG), pectin methyl esterase (PME), galactanase, arabinanase and β ‐galactosidase. They all showed a climacteric peak in activity during ripening, except for PME which showed a continuous decrease in activity after an initial increase. These results are discussed in the light of fruit softening during ripening. Copyright © 2003 Society of Chemical Industry     

双组份SO2-ClO2保鲜剂对红提葡萄采后软化相关酶的影响

为探讨双组份SO2-ClO2保鲜剂抑制葡萄果实成熟软化的关键酶,以新疆红提葡萄为试材,研究双组份SO2-ClO2保鲜剂对葡萄果实中果胶和软化酶系的影响,并对果实内软化相关酶的变化进行比较分析,结果表明双组份SO2-ClO2可抑制果实内原果胶（TP）水解,减缓可溶性果胶（WSP）的增加,延缓果实硬度的降低;同时抑制果胶甲酯酶（PME）、多聚半乳糖醛酸酶（PG）、果胶裂解酶（PL）、纤维素酶（Cx）和β-半乳糖苷酶（β-Gal）等几种细胞壁软化相关酶的活性,从而可延缓果胶和纤维素的降解,较好保持葡萄果实的硬度。      

Unravelling process-induced pectin changes in the tomato cell wall: An integrated approach

The activity of the pectin-modifying enzymes pectin-methylesterase (PME) and polygalacturonase (PG) in tomato fruit was tailored by processing. Tomatoes were either not pretreated, high-temperature blanched (inactivation of both PME and PG), or high-pressure pretreated (selective inactivation of PG). Subsequently, two types of mechanical disruption, blending or high-pressure homogenisation, were applied to create tomato tissue particle suspensions with varying degrees of tissue disintegration. Process-induced pectin changes and their role in cell-cell adhesion were investigated through in situ pectin visualisation using anti-pectin antibodies. Microscopic results were supported with a (limited) physicochemical analysis of fractionated walls and isolated polymers. It was revealed that in intact tomato fruit pectin de-esterification is endogenously regulated by physical restriction of PME activity in the cell wall matrix. In disintegrated tomato tissue on the other hand, intensive de-esterification of pectin by the activity of PME occurred throughout the entire cell wall. PG was selectively inactivated (i.e. in high-pressure pretreated tomatoes), with de-esterification of pectin by PME, which resulted in a high level of Ca²⁺-cross-linked pectin and a strong intercellular adhesion. In non-pretreated tomato suspensions on the other hand, combined PME and PG activity presumably led to pectin depolymerisation and, hence, reduced intercellular adhesion. However, because of the high amount of Ca²⁺-cross-linked pectin in these samples, cell-cell adhesion was still stronger than in the high-temperature blanched tomatoes, in which the absence of PME activity during suspension preparation implied few Ca²⁺-cross-linked pectic polymers and extensive cell separation upon tissue disruption.     

SOFTENING AND BIOCHEMICAL CHANGES OF SAPOTE MAMEY FRUIT (POUTERIA SAPOTA) AT DIFFERENT DEVELOPMENT AND RIPENING STAGES

We investigated some of the physicochemical and biochemical factors associated with flesh softening of sapote mamey fruit during development and ripening. The activities of pectinmethylesterase (PME), polygalacturonase (PG) and β‐galactosidase (β‐GAL) enzymes were measured in fruits harvested at different development stages, and postharvest in two production seasons. The textural changes were most noticeable at the preclimacteric stage in ripening fruit. The water‐soluble pectin (WSP) increased at a different rate than firmness decreased. No correlation between PG or PME activity and changes in firmness was observed in ripening fruits, though a low correlation was seen between β‐GAL activity and softening in climacteric stage. Greatest loss of firmness occurred in climacteric stage. Fruit pulp softening was not dependent on a single enzyme activity.     

Impact of exogenous salicylic acid treatment on the cell wall metabolism and ripening process in postharvest tomato fruit stored at ambient temperature

Tomato is a climacteric fruit susceptible to rapid softening and ripening after harvest. In this study, the changes of physicochemical characters, cell wall-degrading enzymes, cell wall compositions and ethylene production of ‘Hisar Arun’ and ‘BSS-488’ tomato fruits were investigated under the influence of salicylic acid treatment. Salicylic acid treatment effectively delayed firmness decline and increase in PLW, TSS and lycopene content. The treated fruits maintained the integrity of cell wall composition by delay in increase in activities of cell wall-degrading enzymes (pectin methylesterase, polygalacturonase and cellulose) and cell wall components (cellulose, hemicellulose, lignin and pectin) decline. Moreover, salicylic acid treatments significantly suppress expression level of ethylene-producing genes (ACO1 and ACS2) and inhibited ethylene production during storage. Overall, the salicylic acid-induced delay in the ripening process occurs via the strong inhibition of ethylene biosynthesis, lowered cell wall-degrading enzyme activities and slowed cell wall degradation.     

Characterising polysaccharides in cherimoya (Annona cherimola Mill.) purée and their enzymatic liquefaction

Polysaccharides isolated in the alcohol-insoluble residues (AIR) from cherimoya (Annona cherimola Mill.) were characterised for contents of soluble pectin, cellulose, hemicellulose and lignin, and the distribution of neutral sugars and uronides in water-soluble pectin (WSP) and water-insoluble AIR (WAIR) fractions. For WSP, the predominant neutral sugar was arabinose and, for WAIR, cellulosic glucose and xylose. Two enzyme preparations were tested for their capacity to release neutral sugars and uronides from WAIR. The optimal incubation temperature (45 °C) and the most effective preparation—rich in pectinase, cellulase and xylanase activities—were selected according to a central composite rotatable design (CCRD). Enzyme was also applied to native cherimoya purée according to another CCRD, varying the enzyme concentration and incubation time. Native purée exhibited strong shear-thinning behaviour with high, extrapolated, yield stress. During enzymatic treatment, behaviour was less shear thinning, and yield stress, consistency index and Bostwick consistency tended to decrease, giving rise to purées of different rheological properties.     

湿冷贮藏对冬枣软化水解酶活性影响的研究

软化是冬枣贮藏中存在的主要问题之一,研究了湿冷贮藏对冬枣不溶性果胶含量和果胶甲酯酶(PME)活性、可溶性果胶含量和多聚半乳糖醛酸酶(PG)活性、纤维素含量和纤维素酶(Cx-cellulases)活性、淀粉含量和淀粉酶活性的影响。结果表明:湿冷贮藏可以延缓冬枣不溶性果胶含量、淀粉含量、PG活性的下降速度,降低可溶性果胶含量、PME活性、Cx-cellulases活性、淀粉酶活性的上升速度,而纤维素含量则表现为先慢后快的增长规律。     

Diverse metabolism of cell wall components of melting and non‐melting peach genotypes during ripening after harvest or cold storage

The mode of change in a range of physiological, physicochemical and biochemical parameters during fruit ripening between distinct peach genotypes (Prunus persica L. Batsch) after cold storage for up to 4 weeks was determined. The nectarine cultivar ‘Caldesi 2000’ was selected as a genotype with melting flesh (MF) characteristic (fruits characterized by extensive flesh softening during ripening) and the cultivar ‘Andross’ as a genotype with non‐melting flesh (NMF) characteristic (fruits characterized by limited flesh softening during ripening). Flesh firmness, ethylene production, physicochemical and biochemical properties of the cell wall were determined and significant differences between the fruits of the two genotypes were recorded. Fruits of the NMF genotype were characterized by higher tissue retention and ethylene production during their ripening, higher content of uronic acids, as well as higher capacity for calcium binding in the water‐insoluble pectin fraction compared with fruits of the MF genotype. Additionally, the ripening of MF‐type fruits was characterized by higher losses of neutral sugars, especially those of arabinose and galactose than the NMF‐type fruits and these losses were more intense after extended cold storage periods. In fruits of the NMF genotype the decreased activity of pectin methyl esterase (PME) combined with higher levels of calcium in the water‐insoluble pectin fraction possibly provided less substrate for polygalacturonase (exo‐, endo‐PG) activity and less solubility of cell wall pectin compared with fruits of the MF genotype. Overall, the data indicate the existence of a wide range of diverse metabolic pathways during fruit ripening of fresh fruits with MF and NMF characteristics. Copyright © 2005 Society of Chemical Industry     

60Co-γ辐照对冷藏蓝莓果实软化相关指标的影响

为探讨辐照对蓝莓果实硬度的影响机制,本研究围绕不同辐照剂量对冷藏蓝莓腐烂率、失重率、果实硬度、细胞壁物质、细胞壁多糖含量以及细胞壁水解酶活性的影响展开系统的研究。结果发现较低剂量的辐照处理（0.5 kGy）对蓝莓冷藏保鲜的效果不显著,较高剂量的辐照剂量（3.0 kGy）加速了冷藏后期蓝莓果实的软化进程,2.5 kGy辐照处理能够降低冷藏期间蓝莓果实中PE（果胶甲酯酶）、PG（多聚半乳糖醛酸酶）、Cx（纤维素酶）三种水解酶的活性,抑制WSP（水溶性果胶）含量升高和ESP（离子型果胶）、SCSP（共价型果胶）、4KSF（连接松散半纤维素）、24KSF（连接紧密半纤维素）含量的下降,从而降低果胶不溶性向可溶性的转变和保证半纤维素的连接作用,最终有效延缓冷藏蓝莓果实软化进程。     

氯吡苯脲处理对莲子细胞壁多糖降解特性的影响

为探究氯吡苯脲（1-(2-chloropyridin-4-yl)-3-phenylurea,CPPU）处理对莲子采后细胞壁多糖降解特性的影响,以‘太空莲36号’莲蓬为试材,以清水浸泡为对照,以5 mg/L CPPU对莲蓬进行处理。结果表明：CPPU处理可有效维持莲蓬及莲子较好的表型,保持莲子脆嫩口感;CPPU处理的莲子含有更高的共价结合果胶含量和更完整的纤维素多糖碳链结构;CPPU处理可有效抑制果胶甲酯酶、多聚半乳糖醛酸酶等果胶降解酶和外切葡聚糖酶、β-葡萄糖苷酶、内切葡聚糖酶等纤维素降解酶的活力,从而延缓共价结合果胶降解及水溶性果胶、离子结合果胶积累,并保持莲子纤维素和半纤维素含量;同时,CPPU处理保持了莲子细胞壁结构和纤维素微纤丝的形态,并抑制了细胞的质壁分离。因此,CPPU处理有利于抑制莲子细胞壁多糖的降解,更好地维持细胞完整性,保持莲子的口感,从而延缓其采后衰老。本实验为鲜莲蓬和莲子的采后保鲜提供理论依据和技术支持。     

VALENCIA ORANGE PECTINMETHYLESTERASE MODIFIED PECTIN CHARACTERIZED BY FOURIER TRANSFORM INFRARED SPECTROSCOPY, CHARGE FRACTIONATION AND GELLING

Pectin was de‐esterified by Valencia orange pectinmethylesterase (PME), fractioned by ion exchange chromatography (IEC) and pooled fractions were characterized for the degree of esterification (%DE) using Fourier transform infrared spectroscopy (FT‐IR), molecular weight (MW) using high‐performance size exclusion chromatography (HPSEC) multi‐angle laser light scattering and calcium gelling properties using texture profile analysis. The experimental %DE of 67.5% was close to the predicted %DE of 67%. The %DE of the pooled pectin fractions decreased slightly with greater elution volume, from 69.3 to 64.0%. The average MW of unfractionated, modified pectin was 268,100. Earlier eluting fractions from IEC had higher MW values near 240,000 than later eluting fractions with MW values near 120,000. PME modified pectin and pectin fractions gelled in the presence of calcium but unmodified pectin did not gel. The hardness and other textural properties of the calcium‐mediated pectin gels were not different among fractions.     

Pectin methyl esterase treatment on high‐methoxy pectin for making fruit jam with reduced sugar content

BACKGROUND: Pectin methyl esterase (PME) has been postulated to catalyse the transacylation reaction between pectin molecules. The present study aimed to prove the occurrence of this reaction. The feasibility of applying PME‐catalysed transacylation between high‐methoxy pectin molecules in making fruit jam with reduced sugar content was also investigated. RESULTS: PME treatment increased the turbidity and particle size in pectin solution and the molecular weight of pectin, while it decreased the number of methoxy ester linkages and the intensity of the CH₃ absorption peak in the Fourier transform infrared spectrum without changes in the number of total ester linkages in pectin molecules. These findings support the occurrence of PME‐catalysed transacylation between pectin molecules. Higher values of hardness, gumminess and chewiness were found in a jam containing PME‐treated citrus pectin (10 g L^?1) and sugar (350 g L^?1) as compared with either a jam containing untreated citrus pectin (10 g L^?1) and sugar (350 g L^?1) or strawberry jam containing pectin (10 g L^?1) from the fruit and sugar (650 g L^?1). CONCLUSION: The demand for sugar in jam making can be greatly reduced by the use of PME‐treated high‐methoxy pectin. Copyright © 2012 Society of Chemical Industry     

Tomato Product Quality from Transgenic Fruits with Reduced Pectin Methylesterase

Juice from transgenic tomato (Lycopersicon esculentum cv Rutgers) fruits with reduced levels of pectin methylesterase (PME) activity due to the expression of a PME antisense gene exhibited improvement in quality. The percentage increase in juice from transgenic fruits over that of juice from wild type Rutgers ranged between 5.1–5.3 for total solids, 3.8–6.1 for soluble solids, 70–80 for efflux viscosity, 180–220 for serum viscosity and about 50 for precipitate weight ratio. Time of harvest had no effect on quality of juice. Ketchup prepared from transgenic fruit juice had a lower Bostwick value, reduced serum separation and high serum viscosity compared to ketchup from parental Rutgers.