Virtual Fruit Tissue Generation Based on Cell Growth Modelling

A cell-growth-based algorithm is presented based on the biomechanics of plant cells in tissues to help explain the typical differences in cellular architecture found between different pome fruit species, cultivars and tissues. The cell was considered as a closed thin-walled structure, maintained in tension by turgor pressure. The cell walls of adjacent cells were modelled as parallel and linearly elastic elements, which obeyed Hooke’s law. A Voronoi tessellation was used to generate the initial topology of the cells. Cell expansion then resulted from turgor pressure acting on the yielding cell wall material. To find the sequence positions of each vertex of the cell walls, and thus, the shape of the cells with time, a system of differential equations for the positions and velocities of each vertex were established and solved using a Runge–Kutta fourth and fifth order (ODE45) method. The model was used to generate realistic 2D fruit tissue structures composed of cells of random shapes and sizes, cell walls and intercellular spaces. Comparison was made with fruit tissue micrographs. The virtual tissues can be used for numerical simulation of heat and mass transfer phenomena or mechanical deformation during controlled atmosphere storage of fresh pome fruit.     

COMPRESSIVE STIFFNESS AND FRACTURE PROPERTIES OF APPLE AND POTATO PARENCHYMA

The compressive mechanical properties of fruit and vegetable parenchyma are related to the morphology of the material such as size, shape and orientation of cells and intercellular spaces, and cellular adhesion. Uni-axial compression tests on geometrical specimens of apple and potato flesh have shown that apple parenchyma is mechanically very anisotropic whereas potato shows no such behaviour. Apple flesh is highly orientated in the cortex into radially elongated cells and intercellular spaces. If the flesh is compressed along the rows of cells (radial) it generally fractures by a collapse of single layer of cells at right angles to the force. If the flesh is compressed at right angles to the rows of cells (tangential) it fails in shear. It is stiffer radially but tougher tangentially requiring greater deformation to fail. There is no orientation of such morphological structures in potato and hence the compressive properties are not dependent on the direction. It always fails in shear. Mature late season apples tend to be stiffer and tougher than early apples as they have smaller cells and thicker cell walls. Early season apples become mealy quickly and cracking occurs by cell separation due to the early breakdown of pectins in the weak intercellular lamellae. This makes them mechanically much weaker than late season apples where cell adhesion is strong and cracking occurs by cell rupture, a process requiring greater force and energy.     

Effect of ultrasound‐assisted osmotic dehydration on cell structure of sapotas

BACKGROUND: Drying is a traditional way of fruit preservation. Because of the high energy costs associated with air‐drying, osmotic dehydration is often applied as a pretreatment to reduce air‐drying time. Ultrasound is an emerging technology with several applications in food processing. The effect of ultrasound on fruit tissue depends on the tissue structure and composition, and ultrasound might be beneficial to improve air‐drying efficiency, with consequent reduction in process costs. In this study the effect of ultrasound and ultrasound‐assisted osmotic dehydration on sapota tissue structure was evaluated. RESULTS: Ultrasound induced cell disruption and breakdown of cells with high phenolic content (dense cells) and also induced elongation of parenchyma cells. Ultrasound application combined with high osmotic gradient enhanced water loss and solid gain because of the formation of microscopic channels. Ultrasound‐assisted osmotic dehydration induced gradual distortion of the shape of cells, cell breakdown and formation of microscopic channels. Micrographs of the fruit tissue showed that ultrasound preferentially affected dense cells. CONCLUSION: Ultrasonic pretreatment was able to preserve the tissue structure of the fruit when distilled water was used as liquid medium. The application of ultrasound‐assisted osmotic dehydration resulted in severe changes in the tissue structure of the fruit, with consequent increase in the effective water diffusivity, because of the formation of microscopic channels and cell rupture. Copyright © 2009 Society of Chemical Industry     

A MEMBRANE MODEL FOR ELASTIC DEFLECTION OF INDIVIDUAL PLANT CELL WALLS

Deformation of plant cells by a fine probe can provide a measure of cell wall stiffness which is responsible for many of the mechanical properties of the plant. An example system of potato tuber parenchyma cells is used, and cell wall deformation approximated as the axisymmetric deformation of a circular membrane made from a nonlinear-elastic material with a Mooney strain energy function. A system of differential equations describing the shape of the membrane is derived and solved. The effects of turgor and initial cell wall strain on the force required to produce a given deflection and on the shape of the deformed cell are examined. Values for the elastic constants of the wall material are proposed, guided by statistical data for cell size and stiffness obtained from micropenetration tests.     

Effects of water loss on apples in storage

Cox's apples were stored for up to 6 months in the presence or absence of anhydrous calcium chloride in an atmosphere containing 2% O₂ and < 1% CO₂ at 3.5°C, and effects on the physical properties of the fruit were assessed for up to 6 months. The desiccant was used to obtain an initial water loss of about 5% of fruit weight in the first 30 days of storage. In control fruit, turgor pressure appeared to be maintained during storage, and fruit volume increased as the air space in the fruit tissue increased. Initial weight loss lowered turgor pressure and prevented this increase. The force required to disrupt slices of apple in the Kramer shear cell was usually higher after initial weight loss, but resistance to the conventional penetrometer was little affected. Initial weight loss led to higher levels of soluble pectin and higher resistance to gaseous diffusion. In sensory tests the high weight-loss fruit was firmer, tougher and less mealy than control fruit.     

采后果品细胞膨压变化规律及其对质地调控的研究进展

细胞膨压是细胞内液体施加在细胞壁上的静水压力,具有维持果品品质的作用。目前,采后果品细胞膨压在贮藏期内的变化规律尚不明确,且细胞膨压与果品质地间的定量关系也未得到充分阐述。因此,本文综述了采后果品细胞膨压的变化规律,以及细胞膨压与果品质地之间的相关性的研究进展。同时,提出了在采后果皮表面和鲜切水果表面构建特殊浸润性涂层,来控制水分定向输送以调控膨压的研究思路。以期为研究贮藏环境因子对采后果品细胞膨压的影响规律提供理论依据,从而突破调节贮藏环境因子阻断细胞膨压损失的关键核心技术,实现果品质地的精确调控。     

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     

MICROSTRUCTURAL FAILURE MECHANISMS IN COOKED AND AGED CARROTS

In situ mechanical testing of hydrated carrot (Daucus carota) parenchymal tissue was performed in an Environmental Scanning Electron Microscope. Carrots were either aged or cooked for varying amounts of time in order to ascertain how these processes affect the mechanical response of the cellular microstructure to being sliced by a scalpel blade. In fresh tissues when the turgor pressure is high, the cells burst in the expected manner. Boiling the tissue reduced the ability of the cells to retain liquid, effecting a transition from closed-cell to open-cell behaviour and the cell walls were torn in tension, behind the blade. Ageing resulted in a drop in the turgor pressure and these materials failed in a manner similar to the fresh, raw tissue except they exhibited a transition in elastic modulus from a pliant to a brittle state when the cells were deformed sufficiently to increase the turgor pressure to the 'fresh' value.     

Voronoi图在蜡印冰纹仿真中的应用

 在绘制数字化的蜡印图案中,为模拟手工蜡印中冰纹自然龟裂的状态,提出一种基于Voronoi图的仿真方法。首先在蜡印图案上随机确定Voronoi 图的基点位置,生成标准Voronoi 图;然后选取位于图案中的Voronoi线段,以Voronoi边界交点作为起点,在原始Voronoi边界的传播方向上加入Perlin噪声,生成新的Voronoi边界;最后通过数目、噪声等控制系数使仿真冰纹接近自然开裂效果,得到最终的仿真蜡印图案。实验结果表明,所提算法模拟出的蜡印冰纹具有较好的连贯性和网络性,符合真实蜡印图案的冰纹特征。     

Effect of turgor pressure on the cutting energy of stored potato tissue

 Potato tissue samples with varying cell turgor pressures were prepared by soaking them in mannitol solutions (0 M to 0.9 M). Increased concentration of mannitol in the soaking solutions decreased the cell turgor pressure in potato tissues, providing samples with varying degrees of turgidity or plasmolysis. The firmness of potato tissues with different turgor pressures was periodically examined over a 12-week period using cutting tests. The occurrence of incipient plasmolysis was evident after soaking in 0.7 M mannitol solution as supported either by microscopic observations or cutting energy values. The cell turgor pressure of unsoaked tissue decreased during the first 2 weeks, increased between 2 and 4 weeks and finally decreased again up to 12 weeks. The cutting energy of unsoaked tissue showed an inverse trend between 2 and 8 weeks, demonstrating the ability of this mechanical parameter to detect the increase of cell wall stiffness as a function of storage time. Received: 8 June 1999     

磷用量对烤烟烟叶发育和结构的影响

１９９２～１９９３年河南宝丰就磷用量对烤烟烟叶发育和叶片结构的影响进行了连续两年的观察研究，结果发现：在一定用量范围内，增施磷肥有促进叶肉细胞分裂，延迟胞间隙分化扩展，促进栅栏组织细胞伸长的作用。磷用量在５６．２５ｋｇ／ｈｍ２以内，增施磷肥既有提高定长叶的叶厚及棚栏组织厚度的作用，又有增加栅栏组织细胞密度，减小胞间隙面积（％）的作用，效果都很明显。磷用量５６．２５～３３７．５０ｋｇ／ｈｍ２，增施磷肥可明显提高定长叶的叶厚及栅栏组织厚度，但对棚栏组织细胞密度及胞间隙面积（％）的影响很小。磷用量超过３３７．５０ｋｇ／ｈｍ２，增施磷肥定长叶的叶厚、栅栏组织厚度及栅栏组织细胞密度降低，胞间隙面积（％）增加。定长叶栅栏组织厚度与叶厚的比值相当稳定，与磷用量的关系不大。     

Microscale modeling of water transport in fruit tissue

A model was developed to describe water transport in fruit tissue, taking into account the microstructural architecture of the cell assemblies in the tissue, which leads to a better understanding of the underlying phenomena causing water loss. Pear (Pyrus communis L. cv. Conference) was chosen as a model system. The fruit tissue architecture was generated by means of a cell growth model. The transport of water in the intercellular space, the cell wall network and cytoplasm was predicted using transport laws using the chemical potential as the driving force for water exchange between different microstructural compartments. The model equations were solved on the pear cortex tissue geometry (referred here after as geometry) using the finite element method. The different water transport properties of the microstructural components were obtained experimentally or from literature. The effective water conductivity of pear cortex tissue was calculated based on the microscale simulations. The values corresponded well with measured values of tissue water transport parameters. The model helped to explain the relative importance of the different microstructural features (intercellular space, cell wall, membrane and cytoplasm) for water transport. The cell membrane was shown to have the largest effect on the apparent macroscopic water conductivity.     

INVESTIGATION OF THE MECHANICS OF SINGLE TOMATO FRUIT CELLS

The mechanical behavior of single tomato fruit cells has been characterized using high strain‐rate microcompression testing. Single cells isolated by gentle washing from inner pericarp tissue were compressed to a wide range of deformations at a speed of 1500 µm/s, and then released. The cells were larger than any tested previously by microcompression, and had very low initial turgor. Force‐deformation data were modeled to find cell wall material properties, assuming water loss during compression could be neglected because of fast compression. Repeat compression‐release experiments were conducted to discover when cell deformation was no longer recoverable upon release. Cells from three commercially grown tomatoes were elastic to deformations of just over 11%. The elastic moduli of the cell walls were found by modeling to be 30 to 80 MPa, significantly lower than suspension‐cultured cell walls. The cell walls yielded at about 2% wall strain. High‐speed compression testing is a powerful tool for studying low turgor cells, such as those found during ripening.     

A Simple Technique to Improve the Firmness of Cooked Potato Tissue

Potato tissue samples with varying cell turgor pressures were prepared by soaking in mannitol solutions (0 to 0·5 M ). Increased concentration of mannitol in the soaking solutions decreased the cell turgor pressure in potato tissues providing samples with varying degrees of turgidity or plasmolysis. Firmness changes in potato tissues of differing turgor pressure during cooking were examined using a Zwick universal testing machine and also by chewing tests. A modified device attached to a Zwick machine facilitated complete immersion of a potato disc in circulating boiling water, providing rapid and reproducible heat transfer in the tissue during firmness measurements. Tissue firmness expressed as the force required to cause 10% strain in the sample varied in potato discs treated with differing mannitol solutions. Potato discs soaked in 0 to 0·3 M mannitol solutions were more turgid at 20°C than other samples and showed higher tissue firmness. However, when discs of potato were heated in the range of 20–90°C, samples treated with 0·4 and 0·5 M mannitol solutions showed some increase in tissue firmness while all other samples exhibited a rapid decline. Bite-force measurements on potato discs also indicated a rapid loss of tissue firmness in turgid samples. Potato tissues when cooked after soaking in 0·4 or 0·5 M mannitol solution showed more intact and inflated cells than other samples. © 1997 SCI     

A new approach for the preservation of apple tissue by using a combined method of xenon hydrate formation and freezing

Freezing usually causes cell and tissue damage in frozen fruits. This study attempted to use a combined method of xenon hydrate formation and freezing (CXF) for the preservation of apple parenchyma tissue and to compare it with the freezing alone process (FAP). CXF included two steps. The first step was to initiate a certain amount of xenon hydrate by introducing the apple parenchyma tissue to the xenon gas at 1.0 MPa and 1 °C for 0, 1, 2, 3, 4, 5, 6 and 7 d. It was found that the amount of xenon hydrate in apple parenchyma tissue increased with storage time and 2 d was optimum to obtain the certain amount of xenon hydrate. In the second step, the sample with optimum xenon hydrate formation was frozen at − 20 °C. The results showed that CXF was more effective in maintaining firmness, turgor pressure, and cell membrane integrity of the apple parenchyma tissue than FAP. A typical restricted diffusion phenomenon which indicates that water molecules are maintained in the apple parenchyma cells was found in the CXF samples, while the FAP samples showed an unrestricted diffusion phenomenon. In addition, firmness, turgor pressure, cell membrane integrity, and restricted diffusion phenomenon of the CXF samples were similar to those of the fresh samples. The CXF could preserve the apple parenchyma tissue because of the bulk water inside the cells and the water surrounding the cells which transformed to ice crystals is limited. Thus, cell and tissue damage due to the formation of ice crystals was reduced. The obtained results indicated that the CXF is effective for the preservation of the apple parenchyma tissue.Industrial relevanceThere has been an attempt to improve the quality of frozen fruit by using innovative techniques, in opposition to simply freezing. This present work proposed xenon hydrate formation for the reduction of bulk water before freezing in order to reduce freezing damage due to a large amount of ice crystal formation. The combined method of xenon hydrate formation and freezing has been proved to be able to reduce cell membrane damage usually occurring in frozen fruit. Thus this new technique has potential to be used for improving the quality of frozen fruit. The xenon hydrate formation is considered as an innovative technique for the preservation of fruit, which is expected to be useful for the frozen food industry.     

采前氯吡苯脲处理对采后‘秦美’猕猴桃细胞超微结构的影响

研究‘秦美’猕猴桃盛花期后28?d用0、10、20?mg/L氯吡苯脲（N-(2-chloro-4-pyridyl)-N’-phenylurea,CPPU）蘸果处理对采后冷藏期猕猴桃果实细胞超微结构的影响。结果表明：CPPU处理加速了猕猴桃果实细胞壁及内部结构的降解,且CPPU质量浓度越大,受损程度越大;10?mg/L?CPPU处理加速了猕猴桃果实淀粉颗粒及胞间质的降解,促使细胞壁弯曲变形及细胞间隙出现,造成猕猴桃果实硬度迅速下降;而20?mg/L?CPPU处理使猕猴桃果实细胞壁严重变形,线粒体严重空泡化,内部结构消失,淀粉颗粒完全降解,细胞间的黏合力丧失。据此认为,CPPU处理加快了猕猴桃果实在贮藏过程中细胞壁、线粒体及淀粉颗粒的降解速度,损坏了细胞器及膜系统的完整性,从而使猕猴桃果实硬度及耐藏性下降,贮藏寿命缩短,品质下降。因此,猕猴桃生产中不建议使用CPPU处理。     

Influence of cultivar,storage and cooking on the mechanical properties of winter squash (Cucurbita maxima)

Texture profile analysis and rupture tests were carried out on raw and cooked tissues of ‘Delica’, ‘CF 2’ and ‘CF 4’ buttercup squash cultivars and ‘Red Warren’ pumpkin during storage. The raw tissues of ‘CF 2’ were the firmest, exhibiting high tissue strength (high failure force) combined with less rigidity, ie lower modulus of deformability (MOD) and higher compressibility (high strain and deformation at failure). ‘Red Warren’ had the least firm tissues combined with high rigidity and low compressibility. The firmness of ‘Delica’ and ‘CF 4’ tissues was intermediate. The texture parameters such as MOD, failure force, hardness, gumminess and chewiness measured on raw and cooked tissues of the four cultivars showed no significant differences up to 2 months of storage but then decreased (P < 0.05) between 2 and 3 months of storage. The size of the cells and thickness of the parenchyma cell walls among ‘Delica’, ‘CF 2’ and ‘CF 4’ were similar. The greater size of ‘Red Warren’ parenchyma cells, larger intercellular spaces and thinner cell walls appear to account for its lower tissue strength compared with the other cultivars. Copyright © 2004 Society of Chemical Industry     

New insights into the dynamics of vacuum impregnation of plant tissues and its metabolic consequences

The complex and highly interconnected intercellular air spaces of plant tissues occupied by gas or native liquid has offered the possibility for impregnation with a wide range of compounds. In food processing, the development of vacuum impregnation has allowed a controlled way to introduce these compounds to the tissue structure aiming at modifying structural, nutritional, and/or functional properties as well as improving the processability of fruits and vegetables. In the last 10 years, more than 100 research articles have been published on the topic and significant insights had been gained including improved understanding of mechanisms for mass transfer as well as the development of new, fascinating industrial applications. In the recent years, our knowledge on these aspects has increased by bringing new exploration technologies for studying the impregnation of porous materials and plant cell physiology approaches to bear on the topic. The aim of this paper is to highlight some of these exciting advances. © 2014 Society of Chemical Industry     

The morphological changes produced in cauliflower stems during pickling, and their relationship to texture parameters

Summary. The changes in morphology and texture which occur during the pickling of cauliflower have been studied using the electron microscope and Instron Universal testing rig.
It has been shown that the marked changes in the texture parameters, hardness, elasticity and cohesion, during the initial 24 hr in brine, correlate with plasmolysis of the tissue and re-organization of cell wall materials. At the end of the 1st week in brine, with the disruption of the protoplast, the only intact organelles were the spherosomes. the cell walls became extremely thin in the pit field regions, and it was to these areas that the spherosomes tended to migrate. the disruption of the spherosomes, during the 4th week in brine, with the possible release of hydrolytic enzymes may have contributed to the further weakening of the cell wall.
The use of electron histochemical stains has permitted the demonstration of the gradual degradation of pectic substances, resulting in enlarged intercellular spaces and a decrease in tissue cohesion. By staining neutral polysaccharides, it has been shown that the cell wall materials are not degraded to a marked extent and hence would add little to the sugars available for bacterial fermentation.
The increase in crispness, said to arise from freshening and acidification, is not just a simple recovery in turgor pressure, since the protoplast plasmalemma quickly loses its semi-permeable characteristics and is later destroyed. However, an enhancement of elasticity and tissue cohesion has been demonstrated by using freshening solutions containing 2500 ppm calcium.     

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.