【作者】 杨宏顺；

【导师】 李云飞；

【作者基本信息】 上海交通大学 ， 制冷及低温工程， 2005， 博士

【摘要】 最大限度地延长果蔬的保鲜期并尽量减少质量损失是果蔬保鲜的主要目标。贮藏技术可延长果蔬的供应期,尤其是水果,目前主要是季节性生产,贮藏技术可以造成返季节供应,既满足消费者的需要,又能保证果农获得较高的利润。人工气调（CA）贮藏一般是通过充氮降氧,并利用果蔬呼吸产生CO₂或充入CO₂造成一定的O₂/CO₂/N₂条件,抑制果蔬的呼吸速率来保藏果蔬。在应用时,一般常配合低温和一定的相对湿度。而自发气调（MA）贮藏利用具有一定透气性的薄膜袋密闭包装果蔬,利用果蔬呼吸改变包装袋内气体成分以抑制果蔬呼吸速率,贮藏中果蔬的呼吸速率和薄膜袋的透气性之间维持动态平衡来维持袋内的气体浓度。定量而有效的评价果蔬质量等级非常重要,贮藏期间果蔬的失水造成的表皮皱缩会严重影响产品的质量等级。研究并制定果蔬表皮粗糙度的定量测定方法及分析评价体系,对客观评价果蔬的商品质量有重要意义。果胶在果蔬细胞壁中起到骨架作用,果胶与半纤维素、纤维素等形成交联结构,共同维持细胞骨架的形态。果蔬的品质特性特别是质构等指标与果胶的结构状态和含量密切相关,而贮藏中果胶的结构和含量变化都有果胶酶的参与,通过研究果胶酶活性的变化和规律可揭示果胶结构与含量的变化,进而可分析与干预果蔬的质构变化。研究果蔬中果胶的结构、含量等变化以及果胶酶活性的变化可深入了解果蔬贮藏中品质变化的一般规律。并可用于和改进气调冷藏条件。本课题研究了果蔬的外在和内部结构变化与品质的关系,首先研究了果蔬表皮在贮藏中表面粗糙度的变化和定量测定,然后研究果胶的超微结构,分析与果胶含量及质地特性间的关系。并对果蔬在气调冷藏下的品质变化动力学进行了初步研究。课题分以下四部分:首先,果蔬表面的失水情况是评价采后果蔬质量的重要指标。提出用原子力显微镜AFM定量测定表皮的粗糙度来表示表面的皱缩程度。用算术平均粗糙度Ra和平方根粗糙度Rq表示。分别研究了MA冷藏下蘑菇（Agaricus bisporus （Lange） Imbach）和CA冷藏下”锦绣”黄桃（Prunus persicu L. Batsch.）的表皮情况。对MA冷藏的蘑菇,贮藏前的算术平均粗糙度为（34.033±5.116） nm,经过2 d贮藏,在2℃,25℃和动态温度自发气调贮藏下其算术平均粗糙度值分别为（40.139±3.359） nm, （65.356±8.253） nm和（43.670±9.280） nm。平方根粗糙度值与算术平均粗糙度值有相似变化趋势,两者均随贮藏时间和温度增加而增大。对CA冷藏下黄桃表皮粗糙度值, CA组与大气冷藏对照组的Ra和Rq值均随贮藏时间延长而增加, CA组的粗糙度值比大气冷藏组的要小,黄桃表皮粗糙度值变化趋势与蘑菇的相似。蘑菇表皮的三维图像直观地表示出水分的蒸发过程,变化趋势符合粗糙度值的变化,特别是贮藏早期阶段（0～2 d）。由粗糙度分析的结果可以区别不同贮藏条件;黄桃中粗糙度值随时间逐渐增加,并且CA组的增加较对照组慢。结果表明原子力显微镜测定的粗糙度指标可有效表示采后蘑菇和黄桃的表面失水情况。其次,利用AFM技术分析果蔬气调冷藏中水溶性果胶（Water-soluble pectin, WSP）和碱溶性果胶（Sodium carbonate-soluble pectin, SSP）的变化情况,特别是果胶链宽、链长和分枝分布情况,分析果胶的结构模型及结构变化的可能方式。对碱溶性果胶,选择2℃下五组人工气调冷藏条件:CA1: 2% O₂+5% CO₂;CA2: 5% O₂ +10% CO₂;CA3: 2% O₂+10% CO₂;CA4: 5% O₂+5% CO₂以及RA:大气冷藏组;对水溶性果胶,选择CA1, CA2和RA组,分析O₂和CO₂浓度对贮藏中桃肉的果胶微观结构的影响。原子力显微镜可观察聚集体和分支的微观结构,时间选择初始,贮藏第15天和第45天。SSP和WSP分子及聚集体在贮藏中逐渐分离,低O₂和高CO₂浓度可抑制SSP和WSP分子的降解。统计结果显示几乎所有AFM观察到的SSP果胶链的宽度都是四个基本单元宽度（11.719 nm, 15.625 nm, 19.531 nm和17.578 nm）的组合,而WSP果胶链宽度基本单元为: 11.719 nm, 15.625 nm, 19.531 nm和35.156 nm。结果表明基本单元之间的平行交联或缠绕结构是黄桃中SSP和WSP分子结构的基本信息。再次,利用TA-XT plus物性仪测定气调冷藏中黄桃的质地变化,并测定了黄桃中果胶酶活性的变化,建立气调冷藏中酶的动力学方程,分析果胶酶活性变化与果实质地特性的关系;研究了2℃下不同气调冷藏条件对黄桃中多聚半乳糖醛酸酶（PG）活性和质地的影响。气体成分选择2% O₂ + 5% CO₂, 5% O₂ + 10% CO₂, 2% O₂ + 10% CO₂, 5% O₂ + 5% CO₂,和大气环境（RA）。以PG前体激活成PG和PG失活成PG转化物为基础,建立气调贮藏下PG酶的动力学数学模型。试验结果表明气调贮藏组的PG激活和失活的反应速率小于大气对照组。这与降低温度对反应速率的影响类似,推测气调对果蔬贮藏中酶活的影响类似于降温作用。贮藏后期硬度值的降低与果胶的分解有关,可能是由于果胶链断裂引起,而与微观上果胶AFM图像结果相对应,测定了气调和大气冷藏下WSP、Chelate-soluble pectin（CSP）和SSP的含量变化,CSP含量与果蔬的质地特性正相关,表明CSP是维持黄桃硬度的重要组成部分。果胶酶活性的变化与硬度及微观结构变化的关系仍需进一步研究。最后,研究气调冷藏条件对果蔬品质货架期的影响。以嫩茎花椰菜为原料,研究了人工气调冷藏对贮藏中维生素C、叶绿素a、叶绿素b、好果率和硬度的影响。通过检测叶绿素和维生素C的变化,试验确定了花椰菜气调贮藏中主要成份的降解为一级反应动力学;根据Arrhenius方程,确定了不同气调贮藏条件下花椰菜主要成份的表观活化能。在两种温度2℃和8℃,两种气体组分3% O₂,2% CO₂,95% N₂和6% O₂,6% CO₂,88% N₂组合条件下贮藏试验,结果表明,在2℃,气体成分为O₂ 3%,CO₂ 2%,N₂ 95%效果较好,贮藏28天后有效商品价值率在84%左右。温度对贮藏的影响大于气调的作用,延长贮藏期的关键是抑制花蕾开放和黄化。全文主要以黄桃为例,选择蘑菇和花椰菜作为某些指标的验证。在微观结构方面,通过研究贮藏中果蔬表皮粗糙度和果肉中果胶的结构变化。同时分析质地和果胶酶活性等宏观品质和生理特性的变化,为从微观结构方面解释和分析果蔬贮藏中生理和品质变化提供理论指导。更多还原

【Abstract】 Extending the shelf-life and maintaining the quality are major goals for the storage of fruits and vegetables （F & V）. Storage technology can prolong the market time for F & V, especially for fruits, since the supply of fruits mainly depends on special seasons of their harvests. Using storage technology off-season supply can be realized, which not only satisfies the market, but also greatly benefits the farmers.The principle of controlled atmosphere （CA） for the F & V storage is to artificially modify the atmosphere in the package and then to inhibit the metabolism of F & V, generally through ventilating the N₂ and utilizing the respiration of F & V to generate the CO₂. It is often companied with low temperature and a certain relative humidity when apply CA storage. The principle of modified atmosphere （MA） storage is to use films with a certain gas penetrability to pack the F & V, utilizing the respiration to change the gas composition in order to inhibit the respiration of F & V itself, and to maintain the balance between the respiration and the penetrability of the films.F & V play an important role in produce trade. It is very important to quantitatively and validly evaluate their qualities. Roughness increase of pericarp from water loss during storage would decrease the marketing value. It is meaningful to research and work out the quantitative determination method and evaluation system of pericarp roughness for impersonally evaluating the marketing value of F & V.Pectin plays a skeleton role in cell walls of F & V, together with semicellulose, cellulose and others to formulate the inter-conjunction structures and maintain the cell shapes. The quality properties, especially texture, have relation with the structures and contents of pectins, and pectinase is very important for changes of pectin structures and contents during storage. Changes of pectin structures and contents can be revealed through the changes of activity of pectinase. Through such changes we can further analyze and manipulate the texture of F & V. Then the general rule of quality changes can be interpreted and used to improve the controlled atmosphere conditions.The main research part can be divided into four parts as follows:The first part is about the visualization and quantitative roughness analysis of fruit skin by atomic force microscopy （AFM） under storage. Skin status of produce is vital in determining fruit quality. Sensory evaluation is often applied to denote this characteristic. A new method, atomic force microscopy （AFM）, was proposed to denote the changes of skin status. Arithmetic roughness （Ra） and root mean square roughness （Rq） of‘Jinxiu’yellow peach （Prunus persicu L. Batsch.） under CA storgage and mushroom （Agaricus bisporus （Lange） Imbach） urder MA storage were analyzed by AFM. For mushroom, the initial value of Ra was （30.035±1.839） nm, while those of 2℃, 25℃and dynamic temperature on the 2 nd day were （40.139±3.359） nm, （54.393±13.534） nm and （41.197±6.555） nm, respectively. This tendency is similar for Ra and Rq. Both values of roughness increased with increasing temperatures during duration of storage. The three-dimensional profile of the pileus epicutis could signify the process of water evaporation intuitionally. The tendency was in accordance with the roughness results, especially for the earlier stage of the storage （0～2 d）. The outcome of roughness analysis could signify the differences of storage conditions. It showed that the roughness measured by atomic force microscopy effectively reflected the moisture loss degree of the mushroom pileus epicutis during post-harvest storage; For yellow peach, the Ra and Rq values increased with storage time in both CA and regular air （RA） storage, and the values of CA group were smaller than that of RA group. There is a linear correlation between Ra and Rq. The three-dimensional profiles of the skins （both mushroom and yellow peach） could also be gained by AFM. The results of yellow peaches indicate that the roughness values increase with the storage time, and the roughness of CA group increases more slowly than that of RA group.The second part is about ultrastructural changes of peach pectin by AFM during CA storage, including water-soluble pectin（WSP） and carbonate-soluble pectin（SSP）. The width, length and branch of the pectin chains were studied. The structural model and the degradation of pectin were also speculated. For SSP, yellow peaches （Prunus persicu L. Batsch.） were stored under controlled atmospheres （CA） of 2% O₂ plus 5%CO₂, 5% O₂ plus 10% CO₂, 2% O₂ plus 10% CO₂, 5% O₂ plus 5% CO₂, and normal atmosphere at 2℃, to investigate the effects of different concentrations of O₂ and CO₂ on the structure of single SSP molecule; for WSP, CA of 2% O₂ plus 5%CO₂, 5% O₂ plus 10% CO₂ and normal atmosphere at 2℃were chosen. The microstructure changes including aggregates and branches were studied by atomic force microscopy （AFM） at initial,on the 15th and 45th day. The microstructures of molecules and polymers （both SSP and WSP） showed that aggregates separated gradually with the storage time. The degradation took place in the linear backbones as well as in side chains. The degradation of SSP and WSP molecules was inhibited by lower O₂ and higher CO₂. Almost all of the SSP chains were composed of four basic units with width of 11.719 nm, 15.625 nm, 19.531 nm and 17.578 nm, while it was 11.719 nm, 15.625 nm, 19.531 nm and 35.156 nm for WSP molecules. The pectin chains can be visualized and calculated exactly by AFM. It indicated that parallel linkage or intertwist between the basic units was fundamental information for both SSP and WSP molecules.The third part is about the texture properties and the pectinase activity of yellow peach under CA storage, the storage conditions were the same as the above for SSP. Kinetic model of polygalacturonase （PG） activity of peaches during CA storage were investigated. Mathematic model was proposed to describe the PG activity based on the formation from inactive predecessor and denaturation into inactive form. The experimental results show that the controlled atmosphere storage groups have lower reaction rate of PG formation and denaturation among different storage groups. The effect of CA on storage may be like that of decreased temperatures. The decrease of the firmness in later stage of storage has relation with the degradation of pectin. This might be result from the breakage of the linkage between pectin chains; the results comply well with the AFM images of pectins. The contents of WSP, chelate-soluble pectin（CSP） and SSP from the peach flesh have been assayed during the storage.There is a linear correlation between the CSP and firmness, it shows that CSP might be essential for maintaining the firmness of peaches. The relationships among the pectinase activity, the firmness and microstructure changes need to be further studied. The fourth part is to investigate the effect of CA conditions on the quality （including ascorbic acid, chlorophyll （a and b）, firmness etc.） and shelf-life of broccoli. The degradations of chlorophyll and ascorbic acid of broccoli under controlled atmosphere storage had been tested and it was found that the degradations followed the first order reaction kinetics. The apparent activation energies of chlorophyll and ascorbic acid of broccoli were also determined, basing on the Arrhenius’s law. The effects of storage temperatures at 2℃and 8℃, and gas compositions of 3% O₂, 2% CO₂, 95% N₂ and 6% O₂, 6% CO₂, 88% N₂,on the broccoli quality were measured. The results showed that the combination of temperature at 2℃, and the gas composition of 3% O₂, 2% CO₂, 95% N₂ was optimal. The broccoli can keep fresh over 28 days with sound ratio over 84%. The function of the storage temperature was found to outweigh the gas composition. The key to extend the shelf-life of broccoli is to inhibit the bud to effloresce and become yellow.Main experimental materials were yellow peaches, companied by mushroom and broccoli to validate some indexes. Quality and physiology properties （texture and PG activity etc.） of postharvest produces were investigated from macro scales, and the roughness of skin and structure of pectin chains from micro scales, which could be used to provide theoretical direction for physiology and quality properties of postharvest produce.更多还原