CO2对果蔬采后生理的作用

研究CO2对果蔬采后生理、成熟衰老机制和果蔬保鲜有重要作用.本文介绍了果蔬采后CO2的生理效应、果实成熟软化过程中细胞壁组分的变化、几种主要的细胞壁降解酶在果实成熟软化中的作用等方面,重点叙述了CO2对果蔬采后果胶酶作用的研究.     

影响桃果实质地的细胞壁降解酶的研究进展

介绍与桃果实质地变化相关的细胞壁降解酶(PG.PE,β-Gal,Cx,XET)在果实成熟过程中的作用.综合表明,桃果实采后的质地变化受多种酶的协同作用,不同酶在桃果实成熟软化的各阶段作用不同,而且各种酶活性变化在不同品种的果实中表现不同.     

硬溶质型桃果实成熟过程中细胞壁多糖降解特性及其相关酶研究

以硬溶质型桃‘晚湖景’为试材,研究细胞壁多糖降解以及细胞壁多糖降解相关酶对硬溶质型桃果实成熟软化的影响。结果表明:硬溶质型桃果实成熟过程中,CDTA-1果胶含量上升,两种Na2CO3溶性果胶含量在成熟末期减少率分别为22.5%和27.4%。KOH溶性果胶含量在整个成熟过程中变化不明显。果实CDTA、Na2CO3组分中果胶多糖主链的断裂、半纤维素和纤维素组分中阿拉伯糖和半乳糖的降解主要发生在成熟末期;β-半乳糖苷酶(β-Gal)与桃果实成熟软化启动密切相关,多聚半乳糖醛酸酶(PG)和纤维素酶(Cx)对桃果实成熟后期快速软化起重要作用。Na2CO3-1溶性果胶多糖的降解与硬溶质型果实采后软化密切相关,KOH-1、KOH-2半纤维素多糖的降解可能促进硬溶质型桃果实成熟软化进程,富含半乳糖醛酸的果胶多糖主链的断裂以及果胶、半纤维素、纤维素中阿拉伯糖、半乳糖等中性糖的降解都可能是果肉软化的重要因素,并有多种多糖降解酶参与其中。     

细胞壁对果实质地影响机制的研究进展

果实质地的改变严重影响采后果实的贮藏运输及其商品价值。而采后果实质地的改变通常认为是由于果实细胞初生壁和胞间层组织中的多糖降解,引起细胞壁超微结构改变所导致的。同时细胞壁多糖降解和多聚物化学键的改变,会进而引起细胞分离、软化、溶胀,改变细胞膨压,从而影响果实质地。多糖降解过程受到一系列细胞壁酶的协同作用,不同酶在果实质地变化的各阶段作用不同,而且各种酶活性变化在不同品种的果实中表现不同。本文主要对细胞壁多糖降解以及其相关酶对果实质地变化的影响进行了系统的分析与展望,总结了果实成熟软化中细胞壁的降解机理,为更好地进行果实贮藏、保鲜及加工提供理论依据。     

贮藏技术对采后水果细胞壁酶影响的研究进展

贮藏过程中采后水果的软化与其细胞壁酶的活性密切相关,细胞壁酶对细胞壁多糖组分的降解和细胞壁结构的破坏是引起水果过度软化导致品质降低的主要原因。有效的采后水果贮藏技术对调控果实相关胞壁酶的活性,延缓水果软化的同时延长其货架期具有重要作用。详细综述不同贮藏技术对水果细胞壁酶的影响,以期为采后水果贮藏技术的选择提供理论依据。     

氯吡苯脲浸泡处理延缓采后芒果成熟和软化的生理机制

以采后‘贵妃’芒果为试材,使用10 mg/L氯吡苯脲（forchlorfenuron,CPPU）溶液对果实浸泡处理10 min,晾干后在室温（25 ℃）条件下贮藏8 d,研究CPPU浸泡处理对芒果果实贮藏期间成熟与软化相关生理指标的影响。结果显示：CPPU浸泡处理明显抑制了芒果果实的呼吸作用并推迟了果肉色泽、硬度、可溶性固形物质量分数和可滴定酸质量分数的变化;CPPU浸泡处理有效抑制了果实1-氨基环丙烷-1-羧酸合成酶和1-氨基环丙烷-1-羧酸氧化酶活性,导致乙烯释放量降低;此外,CPPU浸泡处理显著抑制了果实多聚半乳糖醛酸酶、果胶甲酯酶、β-半乳糖苷酶等果胶水解酶活性变化,并较大程度抑制了果胶多糖的增溶与解聚作用,故而延缓了果实的软化进程。结论：CPPU浸泡处理能有效延缓采后芒果果实的成熟与软化,从而延长果实货架寿命。     

采收期对京白梨果实细胞壁代谢及货架品质的影响

研究了不同采收期京白梨果实后熟软化过程中细胞壁代谢和货架品质的变化。结果表明,采期Ⅰ和采期Ⅱ果实硬度大,叶绿素含量高,可溶性固形物含量低,呼吸速率不稳定,软化进程缓慢。采期Ⅱ的果实细胞壁代谢与采期Ⅲ、采期Ⅳ和采期Ⅴ存在显著差异,表明果实成熟度不够。采期Ⅴ果实无明显呼吸跃变峰,细胞壁酶活性高,果实软化后易衰老,货架期短,表明该期果实已经完熟。而采期Ⅲ和采期Ⅳ(盛花后135 d~142 d)的果实呼吸、细胞壁代谢、品质变化正常,具有适宜的采收成熟度。     

糖代谢对甜瓜果实后熟软化的影响

为研究糖代谢及其基因表达与甜瓜果实后熟软化的关系,将甜瓜果实分别在20、2℃下直接贮藏、1-MCP处理后在20℃下贮藏,测定果实后熟软化过程中硬度、呼吸速率、乙烯释放量、淀粉和可溶性糖含量及相关酶活性,并对其关键酶基因(AM、SPS、SS和AI)进行实时荧光定量PCR分析。结果显示,甜瓜果实采后淀粉快速降解,在此过程中,果实硬度也迅速下降,淀粉酶(amylase, AM)是果实软化初期的关键酶。在果实后熟软化过程中,蔗糖、果糖和葡萄糖含量均有所下降,蔗糖代谢也参与了甜瓜果实后熟软化。此外,低温和1-MCP处理对甜瓜果实糖代谢、淀粉代谢过程中酶活性与相关基因表达均有抑制作用。     

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。     

果胶降解与采后果实质地变化研究进展

果胶是高等植物细胞壁的重要组成成分,对于维持细胞结构起着重要作用。果胶与果实成熟软化过程中质地变化密切相关。本文综述了果胶的一般化学结构、结构模型、采后果实果胶的含量与组分变化、中性糖组成与多聚物纳米结构的变化,总结了采后不同质地变化类型果实的果胶降解模式,为深入认识果胶代谢在不同质地变化类型果实中的作用提供参考。     

The linkage between cell wall metabolism and fruit softening: looking to the future

The softening that accompanies ripening of commercially important fruits exacerbates damage incurred during shipping and handling and increases pathogen susceptibility. Thus, postharvest biologists have studied fruit softening to identify ways to manage ripening and optimise fruit quality. Studies, generally based on the premise that cell wall polysaccharide breakdown causes ripening‐associated softening, have not provided the insights needed to genetically engineer, or selectively breed for, fruits whose softening can be adequately controlled. Herein it is argued that a more holistic view of fruit softening is required. Polysaccharide metabolism is undoubtedly important, but understanding this requires a full appreciation of wall structure and how wall components interact to provide strength. Consideration must be given to wall assembly as well as to wall disassembly. Furthermore, the apoplast must be considered as a developmentally and biochemically distinct, dynamic ‘compartment’, not just the location of the cell wall structural matrix. New analytical approaches for enhancing the ability to understand wall structure and metabolism are discussed. Fruit cells regulate their turgor pressure as well as cell wall integrity as they ripen, and it is proposed that future studies of fruit softening should include attempts to understand the bases of cell‐ and tissue‐level turgor regulation if the goal of optimising softening control is to be reached. Finally, recent studies show that cell wall breakdown provides sugar substrates that fuel other important cellular pathways and processes. These connections must be explored so that optimisation of softening does not lead to decreases in other aspects of fruit quality. Copyright © 2007 Society of Chemical Industry     

Fruit ripening phenomena--an overview

Fruits constitute a commercially important and nutritionally indispensable food commodity. Being a part of a balanced diet, fruits play a vital role in human nutrition by supplying the necessary growth regulating factors essential for maintaining normal health. Fruits are widely distributed in nature. One of the limiting factors that influence their economic value is the relatively short ripening period and reduced post-harvest life. Fruit ripening is a highly coordinated, genetically programmed, and an irreversible phenomenon involving a series of physiological, biochemical, and organoleptic changes, that finally leads to the development of a soft edible ripe fruit with desirable quality attributes. Excessive textural softening during ripening leads to adverse effects/spoilage upon storage. Carbohydrates play a major role in the ripening process, by way of depolymerization leading to decreased molecular size with concomitant increase in the levels of ripening inducing specific enzymes, whose target differ from fruit to fruit. The major classes of cell wall polysaccharides that undergo modifications during ripening are starch, pectins, cellulose, and hemicelluloses. Pectins are the common and major components of primary cell wall and middle lamella, contributing to the texture and quality of fruits. Their degradation during ripening seems to be responsible for tissue softening of a number of fruits. Structurally pectins are a diverse group of heteropolysaccharides containing partially methylated D-galacturonic acid residues with side chain appendages of several neutral polysaccharides. The degree of polymerization/esterification and the proportion of neutral sugar residues/side chains are the principal factors contributing to their (micro-) heterogeneity. Pectin degrading enzymes such as polygalacturonase, pectin methyl esterase, lyase, and rhamnogalacturonase are the most implicated in fruit-tissue softening. Recent advances in molecular biology have provided a better understanding of the biochemistry of fruit ripening as well as providing a hand for genetic manipulation of the entire ripening process. It is desirable that significant breakthroughs in such related areas will come forth in the near future, leading to considerable societal benefits.     

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.     

苹果采后软化过程中糖类物质代谢的研究进展

苹果果实的后熟软化是一个复杂的生理过程,受多种因子调节。本文综述了细胞壁多糖在软化过程中的代谢变化和它对果实后熟软化生理的重要调节作用;可溶性糖和淀粉的代谢变化不仅对于果实风味品质的形成有重要作用,更是维持果实细胞膨压的重要因素,可能是果实软化的另一个关键因素。     

Mango ripening – Role of carbohydrases in tissue softening

A range of cell wall degrading enzymes, both glycanases and glycosidases, was identified in ripe mango (Mangifera indica cv. Alphonso) fruits. Reduction in the mannose content of the hydrolyzed polymeric fractions of ripe mango revealed the possible involvement of an endomannanase and α-mannosidase, the two major enzymes, in mango fruit softening and ripening phenomena. α-Mannosidase was resolved into isoforms I and II by chromatographic methods and their kinetic and inhibition properties were studied.     

Isolation,purification and characterisation of polygalacturonase from ripened banana (Musa acuminata cv. Kadali)

Bananas are the most important fruit crop in the world. Short shelf life of the fruit is the major limiting factor in international trade, and this is due to the softening of the pulp during ripening. Fruit softening is an important aspect of ripening process in fleshy fruits and is caused by the cumulative action of a group of cell wall‐modifying enzymes. Polygalacturonase (PG) is the key enzyme involved in the fruit softening process in banana, and this study reports the isolation, purification and characterisation of polygalacturonase enzyme from ripened fruits of a delayed ripened banana cultivar found specifically in Kerala (Musa acuminata cv. Kadali). PG was purified by ammonium sulphate fractionation followed by DEAE cellulose ion exchange chromatography and gel filtration using Sephadex G 100. The purified protein showed two subunits on SDS‐PAGE and a single band on native PAGE. Enzyme showed maximum activity at pH 3.5 and 40 °C. Fe³⁺ enhanced the activity more, while Mg²⁺ and Ca²⁺ slightly stimulated the activity of purified enzyme. Km value for substrate polygalacturonic acid was 0.06%.     

EFFECT OF GAMMA IRRADIATION ON SOFTENING CHANGES AND ENZYME ACTIVITIES DURING RIPENING OF PAPAYA FRUIT

The aim of this work was to study the role of cell wall and ethylene related enzymes to papaya fruit firmness. Irradiation treatment was used as an imposed stress to cause changes in firmness. Physiologically mature papaya fruits were irradiated (500 Gy) and allowed to ripen at 22C and 90% RH. Polygalacturo‐nase (PG), pectinmethylesterase (PME), βgalactosidase, cellulose and 1‐aminocyclopropane‐1‐carboxylate oxidase (ACC‐oxidase) activities were followed during ripening and correlated to changes in firmness, skin and pulp color, respiration and ethylene production. The firmness of irradiated fruits was retained at least 2 days longer than in normal fruits and also had a slower rate of softening. Total soluble solids (d?Brix), cellulase activity and ethylene production were not altered by irradiation treatment. The activity patterns of PG, PME and β‐galactosidase were related to pulp softening and affected by irradiation. ACC‐oxidase activity was influenced by irradiation treatment, but its changes were not temporally related to those in firmness. It was concluded that irradiation had no direct effect on firmness but it acted by altering the ripening induced synthesis of cell wall enzymes, mainly PME.     

Polygalacturonase (PG) gene expression in <Emphasis Type="Italic">Musa acuminata</Emphasis> cultivars from Kerala

Banana cannot be preserved for a long time after harvesting due to a short shelf life. Fruit softening is associated with textural changes due to disassembly of the primary cell wall and modification of the structure and composition of various polysaccharides. Cell wall degradation is caused by the action of various cell wall hydrolase enzymes. Polygalacturonase (PG) is the key enzyme involved in this process. The ripening period is different in cultivars maintained under domesticated cultivation in Kerala. PG activity was profiled in eight Musa acuminata cultivars from Kerala and expression analysis of the PG gene was accomplished using semi-quantitative RT-PCR. Maximum PG activity was observed in Palayankodan and minimum activity was observed in Kadali. Gene expression analysis showed variation between ethylene treated fruits and controls in Palayankodan, whereas the expression patterns in Kadali were similar. The fruit softening process is cultivar specific.     

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