果实成熟软化与相关的酶学研究

果实采后仍然是活的有机体,其后熟软化是一个复杂的生理生化变化过程,其中细胞壁降解酶起着重要的调控作用。综述了与果实成熟软化相关的胞壁酶(多聚半乳糖醛酸酶、纤维素酶、果胶甲酯酶、β-半乳糖苷酶)在果实成熟衰老和软化过程中的作用和活性变化规律,为抑制果实采后软化、延长贮藏期提供理论依据。     

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。     

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。     

柿子后熟过程中生理代谢和品质变化及乙烯的催熟效果

牛心柿后熟过程中,果实呼吸强度和乙烯释放速率出现明显跃升现象,果实硬度、总酸度和维生素C含量下降,还原糖和总糖含量上升。果实的品质变化早于生理代谢变化。1000 10~(－6)乙烯处理明显促进果实后熟,可作为柿子产销中提高商品质量的一项技术措施。     

蕃茄短期高溫贮藏

很多果实收获后进行追熟,产生明显的着色、变香及软化等现象。这种一系列的追熟现象,认为是由于乙烯和其他激素使果实内产生代谢转换的结果。此外,追熟现象还受到外界环境的显著影响。调节     

鲜枣软化生理变化和关键影响因子的研究进展

果实的软化是一个非常复杂的发育调控过程,其间经历了一系列生理生化的变化。本文就鲜枣软化的研究进展进行了综述,包括与鲜枣软化过程相关的生理变化,即果皮和果肉颜色的变化、脱落酸和乙烯含量的变化、主要水解酶活性的变化、乙醇、LOX活性、AAO活性、PPO活性的变化和鲜枣软化过程中超微结构的变化,以及影响鲜枣软化过程的品种、成熟度和环境条件因素。     

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.     

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。     

1-MCP对猕猴桃包装贮藏生理的影响研究

猕猴桃属典型的呼吸跃变型果实,具有明显的生理后熟过程,采后如不及时处理极易软化腐烂,所以对猕猴桃贮藏生理的研究刻不容缓。本研究以皖翠、金魁、海沃德三个品种的猕猴桃为试材,通过定期的检测观察,研究了不同贮藏温度下,1-MCP对猕猴桃生理生化特性的影响,结果表明:1-MCP能降低贮藏期猕猴桃的呼吸作用,酸、VC含量、果实硬度变化较小,并提出了最佳贮藏模式,为商业流通和加工企业的猕猴桃包装贮藏提供了理论依据。     

运输振动对水果贮藏品质影响的研究进展

为探寻长途运输过程对采后水果贮藏品质造成影响的机理,本文主要对目前各类水果经模拟运输振动处理后品质变化的研究成果进行了综述。水果在人们日常膳食中的重要组成部分,本文通过分别阐述国内外水果贮运的发展现状,比较总结出国内目前农产品长途运输方式存在的欠缺。概述了水果振动损伤特性研究现状,并总结了模拟运输振动的方法及其影响因素。另外本文分别从果实的外观、营养、风味品质变化以及果实的后熟软化、呼吸乙烯速率变化以及抗氧化四个方面着重分析了运输振动对水果采后贮藏品质特性影响的研究进展,总结得出长途运输过程会导致果实发生形变、营养成分比例降低以及风味口感改变,还会加速果实的后熟软化以及呼吸乙烯释放速率,最后在此基础上提出了目前水果运输振动研究存在的不足和未来的研究方向。     

Cell Wall Changes and Partial Prevention of Fruit Softening in Prestorage Heat Treated ‘Anna’ Apples

Prestorage heat treatment (38°C for 4 days) retarded the softening of ‘Anna’ apple fruits during 0°C storage. Fruit softening of unheated apples during storage was accompanied by changes in pectic substances: a decrease in uronic acid content in the carbonate-soluble fraction and an increase in the water-soluble fraction. Heat treatment partially inhibited the degradation of uronic acids in the cell wall. The degree of pectin methylation in both heated and non-heated fruit decreased during storage. In heat treated apple fruit the content of galactose and arabinose in the cell wall decreased during storage; in non-heated fruit only galactose decreased. We suggest that the inhibition of solubilisation of the carbonate soluble pectin fraction is one of the main factors contributing to the firmness retention caused by heat treatment. The loss of both arabinose and galactose in heat treated fruits may also play an as yet undefined role in the effect of heat treatment on fruit softening.     

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     

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。     

Gamma-Radiation Affects Cell Wall Composition of Strawberries

Tissue softening limits the use of gamma irradiation for controlling postharvest microbial development on some produce. The carbohydrate composition of the cell wall of the strawberry (Fragaria ananassa Duch. cv. Chandler) fruit and of cell wall fractions was compared in untreated controls and in fruit irradiated at 4 kGy, a dose causing tissue softening. Cell wall polysaccharides were partially degraded, particularly cellulose and pectic substances. However, neutral sugars from the pectic and hemicellulose fractions were not affected by irradiation, in contrast with cell wall degradation during ripening.     

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.     

海藻酸钠/纳米TiO2复合涂膜对采后番木瓜果实软化及细胞壁降解影响

为探究海藻酸钠/纳米TiO₂(sodium alginate/nano-TiO₂,SA/TiO₂)复合涂膜处理抑制采后番木瓜果实软化的作用机理,以“日升10号”番木瓜为试材,采用SA/TiO₂复合涂膜处理,研究采后番木瓜果实硬度、细胞壁组分含量和细胞壁水解酶活性的变化规律。结果表明,SA/TiO₂复合涂膜处理能有效地抑制采后番木瓜果实中多聚半乳糖醛酸酶(polygalacturonase,PG)、果胶甲酯酶(pectin methylesterase,PME)、纤维素酶(cellulase,Cx)和β-半乳糖苷酶(β-D-galaetosidase,β-Gal)活性,减缓原果胶和纤维素的水解,减少可溶性果胶的增加,从而保持较完整的细胞壁结构,维持果实硬度。因此认为,SA/TiO₂复合涂膜处理可延缓采后番木瓜果实的软化进程,提高果实耐贮性。     

Fruit softening correlates with enzymatic activities and compositional changes in fruit cell wall during growing in Lycium barbarum L.

The present study aims to examine fruit cell wall-associated fruit softening in Lycium barbarum L. by the microstructure of the fruit cells and the changes in the contents of cell wall components, molecular weights of cell wall polysaccharides and the activities of related cell wall degrading enzymes at different development stages of L. barbarum L. fruit. Fruit firmness significantly declined during ripening, with the greatest reduction between the 28 and 35 days stages. The decrease in firmness correlated with an extensively deformed microstructure in the parenchyma tissues and positively correlated with reductions in the contents of fruit cell wall materials and molecular weight in cell wall polysaccharide. Cellulase, α-galactosidase, polygalactosidase and pectin methylesterase showed higher activities during 28 days; whereas, the activities of β-galactosidase were higher during 35 days. These results indicate that cell wall-related processes are a key feature of early softening in L. barbarum L.     

Early post-veraison growth in grapes: evidence for a two-step mode of berry enlargement

An account is provided of berry softening plus cell wall loosening in flesh and skin tissues, that relates to changes in berry turgor and sugar accumulation around veraison in Golden Muscat ( Vitis vinifera × V. labrusca ). The onset of change in berry deformability was taken as a demarcation between pre-veraison and post-veraison growth phases. Our results confirmed that post-veraison berry enlargement was preceded by berry softening and sugar accumulation. Berry 'turgor' (as inferred from the rate of juice exudation from punctured fruit) increased abruptly and concurrently with berry softening and sugar accumulation, but dropped steadily with subsequent berry expansion. Elasticity of skin tissues decreased abruptly during early phases of expansion, while berry deformability increased. We suggest that cell wall loosening in flesh tissues precedes cell wall loosening in skin tissues, and that this loosening sequence results in a two step sequence where berry softening is later followed by berry expansion.     

NO处理对采后莲雾果实絮状绵软进程的影响

探明NO处理对采后莲雾果实成熟衰老过程中絮状绵软进程的影响。以台湾‘黑珍珠’莲雾果实为材料,用不同用量（5、10、20 μL/L）外源NO熏蒸处理莲雾果实,以0 μL/L NO熏蒸处理作对照,研究其对采后莲雾果实生理及品质、细胞壁代谢及木质素代谢的影响。结果表明：与对照相比,不同用量外源NO熏蒸处理能够显著抑制莲雾果实贮藏过程中絮状绵软指数及质量损失率的上升,保持果实硬度,延缓果实纤维素含量的下降,10 μL/L NO显著降低了多聚半乳糖醛酸酶（PG）、果胶甲酯酶（PME）、β-半乳糖苷酶（β-Gal）活性。同时,不同用量外源NO熏蒸处理能够延缓果实木质素含量的上升,10 μL/L NO显著降低了苯丙氨酸解氨酶（PAL）、过氧化物酶（POD）、4-香豆酸辅酶A连接酶（4-CL）活性。相关性分析表明,絮状绵软指数与质量损失率、果肉硬度、纤维素含量和木质素含量之间均存在显著相关性,且与原果胶含量呈极显著负相关,与可溶性果胶含量呈极显著正相关。NO处理能够抑制细胞壁类物质降解酶活性,延缓采后莲雾果实絮状绵软进程,延长果实贮藏期,其中以10 μL/L NO处理效果最好。