Internal mechanical damage prediction in tomato compression using multiscale finite element models

The mechanical damage of exocarp, mesocarp and locular gel tissues of three and four locular tomatoes subjected to an external compressive force were predicted using multiscale finite element models. The simulation factors consisted of three loading positions and five external forces. Results showed that the locular gel tissue would have mechanical damage prior to the mesocarp and exocarp tissues as force was applied to the fruit. Internal structural characteristics of the tomato had an obvious effect on the mechanical damage behavior of the tissues. The deformed displacement of the tissues was highest for four locular tomatoes compressed at a position midway between adjacent cross walls (P2) and was lowest for four locular tomatoes compressed from a position at the cross wall (P3) at the same external force. The simulated data confirmed the experimental results and were able to predict the internal mechanical damage of tomatoes.     

Diffusion of carbon dioxide in tomato fruits during cold storage in modified atmosphere

Treatments with 20% CO₂ of tomato fruit produced a beneficial extension of storage life. The diffusion of CO₂ in tomato (Lycopersicon esculentum Mill) cv. Platense was measured chromatographically and the concentration profiles in the internal gaseous atmosphere of the fruit were determined for non-steady state conditions to establish minimum treatment times that can ensure adequate penetration of the gas.
The effective diffusivity of CO₂ in the tissue was determined by fitting concentration data, obtained from experiments with whole fruit without skin, to the non-steady state solution of the diffusion equation, assuming negligible external mass transfer resistance. The diffusivity was modelled using Maxwell-Eucken expressions, taking account of the heterogeneous structure of the tissue.
The resistance of the fruit skin was evaluated using whole fruits with the stem scar covered with paraffin and fitting experimental data to the solution in terms of mass Biot number; the specific resistance of the peel was some 200 times greater than that of the stem scar.     

Mechanical properties of tomato exocarp,mesocarp and locular gel tissues

In order to accurately predict the internal stress distribution and damage region of tomato fruit subjected to an external force using finite element method, the tomato fruit can be regarded as a multibody system which consists of exocarp, mesocarp and locular gel tissues. In the paper, these tissues’ mechanical properties of two tomato varieties were determined using different types of test. Results showed the tension failure stress and elastic modulus of exocarp tissue varied from 0.421 to 0.582 MPa and 4.601 to 9.59 MPa respectively; the compression failure stress and elastic modulus of mesocarp tissue varied from 0.122 to 0.229 MPa and 0.726 to 0.846 MPa respectively; the compression failure stress and elastic modulus of locular gel tissue varied from 0.012 to 0.016 MPa and 0.048 to 0.124 MPa respectively; the failure stress and elastic modulus values of outer layer tissue of tomato fruit were higher than those of inner layer tissue.     

Mechanical Models of Compression and Impact on Fresh Fruits

Well‐designed and well‐operated postharvest mechanical handling processes are vital if fresh fruits are to enter markets with minimal damage. The susceptibility of fruit to quality loss during handling is largely determined by mechanical contact and damage. This article reviews current understanding concerning the effect of impact and other mechanical contacts on fruits. It also discusses the major mechanical models that represent the interaction between fruits or a fruit and a surface. In total, 25 mechanical models associated with compression and impact behaviors of fresh fruits, mainly characterizing such behavior between 2 deformable spherical bodies and between a deformable spherical body and a rigid plate are reviewed. Finally, possible future research directions are discussed. The main challenge in fruit handling is to recognize and prevent microscopic damage to fruits, especially internal tissue/cell damage and microcracks resulting from multiple/repetitive impacts and compressions.     

Difference in volatile composition between the pericarp tissue and inner tissue of tomato (Solanum lycopersicum) fruit

Numerous studies have reported the volatile profiles in the whole fruit or pericarp tissue of tomato (Solanum lycopersicum) fruit; however, information is limited on the volatile composition in the inner tissue and its contribution to tomato aroma. For this, the pericarps and inner tissues of “Moneymaker,” “UglyRipe,” and “FL 47” fruits were separated before volatile analysis. Result showed that the volatile profiles were quite similar between the pericarp and inner tissue, suggesting the inner tissues also have a contribution to overall aroma quality. Besides the difference in volatile profile among cultivars, a higher concentration of alcohols was observed in the inner tissues of tomato fruit in comparison with that in the pericarp, which was associated with higher levels of 3‐methylbutanal, 2‐methylbutanal, 3‐methylbutanol, and 2‐methylbutanol in the inner tissue. These results also imply that different sampling methods might impact tomato aroma quality, which needs further verification via sensory penal.

Practical applications

The information on the volatile profile in the inner tissue and its contribution to tomato aroma is still rudimentary. In this study, the pericarp and inner tissue were separated from three tomato cultivars of different genetic background, and the volatile compositions were analyzed with HS‐SPME‐GC‐MS. Result showed that the volatile compositions were quite similar between the pericarp and inner tissue, suggesting that the inner tissues also have a contribution to overall aroma quality. Besides, a higher concentration of alcohols was observed in the inner tissues of tomato fruit in comparison with that in the pericarp, which was associated with higher levels of 3‐methylbutanal, 2‐methylbutanal, 3‐methylbutanol, and 2‐methylbutanol in the inner tissue. This study will provide the researchers and consumers some useful information on volatile composition in the inner tissue, its contribution to tomato aroma, and the impact of different sampling methods on the volatile profile.     

Study of the suitability of HRMAS NMR for metabolic profiling of tomatoes: Application to tissue differentiation and fruit ripening

The feasibility of HRMAS NMR as an efficient technique for metabolic studies of tomato fruit and tomato tissues is described. A good-taste tomato variety from Almería (Spain) (commercial name Zayno) was chosen for this study. Fruits of three different ripening stages (green, turning and red) were selected, based on their external appearance. NMR data of whole fruits were obtained through ¹H HRMAS NMR spectra of tomato purée. Flesh, peel and seeds from mature red fruits were separately analysed. ¹H HRMAS NMR spectra showed resolutions similar to that of solution ¹H NMR with the advantages of minimal sample manipulation and possibility of analysing polar and non-polar compounds simultaneously. Seeds could be clearly distinguished by visual comparison of the spectra. Tryacylglycerols, in which linoleic (47%) and oleic (28%) acyl chains preponderate, were the major components of seeds. By contrast, signals of fructose, glucose, citric acid, and the amino acids GABA, glutamine and glutamate dominated the spectra of flesh, peel and tomato purée. Principal components analysis, performed on the covariance matrix, revealed a clear separation between peel and flesh. Apart form the presence of the cutin biopolymer, peel showed a specific accumulation of sugar and sugar moieties related to pectin degradation, as well as glycosylated metabolites. Chemometric analysis also allowed the metabolic trajectory from green to red mature stages to be visualised. However, sample heterogeneity in the analysis of the whole fruit proved to be an important issue. The source of such heterogeneity was assigned to the presence of tissues of different hardness in the small amount of sample used. The presence of two clusters of samples at the turning stage indicated that the levels of certain metabolites could diverge significantly in fruits with almost identical appearance.     

CREEP BEHAVIOUR OF TOMATO PERICARP TISSUE AS INFLUENCED BY AMBIENT TEMPERATURE RIPENING AND CHILLED STORAGE

The influence of normal ripening and chilling stress on viscoelastic properties of tomato pericarp tissue were investigated by measuring creep behaviour of tissue from fruit stored at 22C (nonchilled) or 5C (chilled) for 28 days, or at 5C for 16 days prior to transfer to 22C for an additional 12 days (prechilled). Creep compliance of tissue from all treatments subjected to a constant shear stress of 150 Pa for 5 min was best represented by a 6-element Burgers model containing two discrete Voigt-Kelvin units characterizing fast and slow rate viscoelastic properties. The magnitude of instantaneous elastic, viscoelastic and steady-state viscous compliances each increased steadily and contributed to the overall softening of nonchilled and prechilled tissues during ripening, but remained unchanged during chilling of tomato fruit. Increased fluidity of ripening tissues occurred at the expense of elasticity, consistent with a decrease in molecular weight-size distribution of structural elements contributing to respective viscoelastic properties. The physico-mechanical changes in prechilled tissue preceded those in nonchilled tissue by several days, and occurred at a faster rate. The 6-element Burgers model defining the creep behaviour of tomato pericarp tissue was interpreted with respect to general plant cell wall structure and biochemical changes known to occur during ripening of tomato fruits. Multiple mechanisms of softening were thereby consolidated into a single physico-mechanical model.     

Texture variation in apricot: Intra-fruit heterogeneity, impact of thinning and relation with the texture after cooking

The rapid texture loss of apricot fruit during storage and transformation is a limiting factor for its commercialisation and use. Apricot flesh exhibits different tissue zones which differ in texture. To better understand texture in apricot fruit, we have studied (i) the intra-fruit heterogeneity of texture measured by puncture test (tissue firmness) (ii) the effect of thinning on whole fruit firmness (global firmness), measured by compression, and on tissue firmness and (iii) the evolution of texture upon steam cooking, on apricots of contrasted texture. Nine tissue zones were defined in fresh apricot fruits in order to study differences in texture from the peduncle to the pistil zones and from the external to the internal tissue. In the nine apricot varieties used, tissue firmness decreased gradually from the external to the internal tissue. However, from the peduncle to the pistil zone, the variation of texture seemed to be variety-dependent. Overall the textures measured for the nine tissue zones were highly correlated, indicative of the major differentiation between soft and firm fruits. However distinct heterogeneity patterns could be observed on axes 2 and 3 of a principal component analysis carried out on the textures of the nine zones. The effect of thinning on fruit firmness appeared variety-dependent. Tissue firmness of the raw apricots assessed by penetrometry explained about two-thirds of the variability of firmness of cooked apricots, versus only 40% for the compression test. High correlations between texture after cooking and prior to cooking were found for four (external equatorial, external pistil, median equatorial and median pistil) out of the nine tissue zones.     

Effect of Number of Locules,Loading Position,and Compression Speed on the Mechanical Behaviors of Tomato Fruits

The mechanical properties of three or four half-ripe locular tomato fruits were characterized by compression testing at 0.5, 1.5, 2.5, 3.5 mm s^?1 to a final deformation of 4% using three loading positions. There was no significant dependence of any of the mechanical parameters on the loading position for these relatively low deformations. However, their dependence on the number of locules and compression speed was highly significant. It is clear that internal structural characteristics and the speed of compression need to be considered in investigations of tomato fruit mechanical behavior.     

The effect of compressibility,loading position and probe shape on the rupture probability of tomato fruits

In this study, factors affecting the rupture probability of tomato fruits were investigated. The experiments were carried out at five compressibility levels (4%, 8%, 12%, 16% and 20%), four loading positions and two probe shapes. The fruit size, shape and mass did not have a significant effect on the rupture probability. The compressibility was the most important independent variable affecting the rupture probability of tomato fruits in the model. The rupture probability of quadrilocular tomato fruit loaded from the cross-wall tissue was the highest, and the odds of being ruptured was 14.5 times higher for quadrilocular tomato fruit loaded from the cross-wall tissue compared to the locular tissue. The curved probe was much more sensitive than the plate probe for rupturing of tomato fruits during the compression tests. It is clear that these investigated factors need to be considered carefully in design and control of tomato harvesting equipment.     

Recent Advance in Aromatic Volatile Research in Tomato Fruit: The Metabolisms and Regulations

Aroma, an essential characteristic of tomato fruit, plays an important role in determining the perception and acceptability of tomato products by consumers. During tomato fruit ripening, associated with color changes from green to red involving the conversion of chloroplasts to chromoplasts are changes of aromatic volatile profiles. Although the biosynthetic pathways for some aromatic volatiles have been established in tomato fruit recently, our knowledge of regulatory mechanisms is still rudimentary. On the other hand, many internal and external factors modify volatile metabolism in tomato fruit. This review first summarizes the current knowledge of expression patterns and biosynthetic pathways of aromatic volatiles in tomato fruit along with the role of ethylene in their biosynthesis. The impact of internal and pre- and postharvest external factors on volatile composition is then discussed. This review will provide critical information for research on tomato aromatic volatiles and their manipulation.     

DEFECTS AND PEELABILITY OF PROCESSING TOMATOES

Peeling is one of the first operations in the manufacture of whole peeled and diced tomatoes, and the peelability of processing tomatoes is significantly affected by the presence of various tomato defects, in particular yellow eye and blossom‐end rot. Tomato maturity also impacts both the percentage of peeled fruit and yield. Immature fruits are typically undercolored and small in size. Sunburned regions on the tomato surface are difficult to peel as well. In this study, we determined the impact of 24 selected tomato defects on tomato peelability and yield of whole peeled tomatoes. There are potential advantages to sorting to remove selected tomato defects early in the process.     

DELINEATION OF PUNCTURE FORCES FOR EXOCARP AND MESOCARP TISSUES IN CUCUMBER FRUIT 1

A puncture test was used to differentiate exocarp (skin) and mesocarp tissues of fresh cucumbers for resistance to penetration. Optimum instrumental test conditions were a punch size of 3.15 mm diameter and crosshead speed of 5 cm/min. The force required to penetrate the exocarp of whole fruit was determined and was deemed to represent a composite of the exocarp and the underlying tissue. By placing 7 mm thick, longitudinal slices skin down on a die plate, failure forces representing the mesocarp and exocarp tissues were determined in fruit ranging from 2.5–5.5 cm diameter. Exocarp force measurements were not influenced by slice thicknesses greater than 1 mm. Mesocarp measurements were lower with thicker slices, and required uniformity of thickness to maximize precision. The exocarp was found to represent about 60% of the composite force required to penetrate whole cucumbers, regardless of fruit size. Toughness of both exocarp and mesocarp increased with fruit size. The relative contributions of exocarp to penetration of seven other fruits varied from 58 to 88%.     

Advances in Machine Vision Applications for Automatic Inspection and Quality Evaluation of Fruits and Vegetables

Artificial vision systems are powerful tools for the automatic inspection of fruits and vegetables. Typical target applications of such systems include grading, quality estimation from external parameters or internal features, monitoring of fruit processes during storage or evaluation of experimental treatments. The capabilities of an artificial vision system go beyond the limited human capacity to evaluate long-term processes objectively or to appreciate events that take place outside the visible electromagnetic spectrum. Use of the ultraviolet or near-infrared spectra makes it possible to explore defects or features that the human eye is unable to see. Hyperspectral systems provide information about individual components or damage that can be perceived only at particular wavelengths and can be used as a tool to develop new computer vision systems adapted to particular objectives. In-line grading systems allow huge amounts of fruit or vegetables to be inspected individually and provide statistics about the batch. In general, artificial systems not only substitute human inspection but also improve on its capabilities. This work presents the latest developments in the application of this technology to the inspection of the internal and external quality of fruits and vegetables.     

Matrix‐Matching as an Improvement Strategy for the Detection of Pesticide Residues

More than 90% of the pesticides residues in apples are located in the peel. We developed a gas chromatography/ion trap tandem mass spectrometry method for investigating all detectable residues in the peel of 3 apple varieties. Sample preparation is based on the use of the Quick Easy Cheap Effective Rugged and Safe method on the whole fruit, the flesh, and the peel. Pesticide residues were quantified with solvent‐matched and matrix‐matched standards, by spiking apple sample extracts. Matrix effects dependent on the type of extract (fruit, flesh, or peel) and the apple variety were detected. The best data processing methods involved normalizing matrix effect rates by matrix‐matched internal/external calibration. Boscalid, captan, chlorpyrifos, fludioxonil, and pyraclostrobin were the most frequently detected pesticides. However, their concentrations in the whole fruit were below European maximum residue levels. Despite negative matrix effects, the residues in peel were detected at concentrations up to 10 times higher than those in whole fruits. Consequently, other pesticide residues present at concentrations below the limit of quantification in the whole fruit were detected in the peel.     

Modeling of Coupled Water Transport and Large Deformation During Dehydration of Apple Tissue

Water loss of fruit during storage has a large impact on fruit quality and shelf life and is essential to fruit drying. Dehydration of fruit tissues is often accompanied by large deformations. One-dimensional water transport and large deformation of cylindrical samples of apple tissue during dehydration were modeled by coupled mass transfer and mechanics and validated by calibrated X-ray CT measurements. Uni-axial compression–relaxation tests were carried out to determine the nonlinear viscoelastic properties of apple tissue. The Mooney–Rivlin and Yeoh hyperelastic potentials with three parameters were effective to reproduce the nonlinear behavior during the loading region. Maxwell model was successful to quantify the viscoelastic behavior of the tissue during stress relaxation. The nonlinear models were superior to linear elastic and viscoelastic models to predict deformation and water loss. The sensitivity of different model parameters using the nonlinear viscoelastic model using Yeoh hyperelastic potentials was studied. The model predictions proved to be more sensitive to water transport parameters than to the mechanical parameters. The large effect of relative humidity and temperature on the deformation of apple tissue was confirmed by this study. The validated model can be employed to better understand postharvest storage and drying processes of apple fruit and thus improve product quality in the cold chain.     

果色和成熟度对樱桃番茄（Solanum lycopersicum var. cerasiforme）果实挥发物分布的影响

为探究果色和成熟度对樱桃番茄果实挥发物的影响,用顶空固相微萃取-气相色谱-质谱联用法测定育种自交系材料金珠（橙）、黑樱桃1（紫）、1号（粉）、红珍珠（红）在绿熟期、转色期和红熟期的挥发物。分析发现,橙色番茄挥发物明显高于红色和粉色番茄。橙色番茄在绿熟期,紫色番茄在转色期和红熟期挥发物最高,而粉色番茄挥发物始终最低。气味强度由挥发物质量浓度和嗅觉阈值决定。3-甲基-丁醛、(E,E)-2,4-庚二烯醛、1-戊烯-3-酮、己醛、苯甲醛和(Z)-3-己烯-1-醇对番茄气味贡献较大。红色、橙色和紫色番茄分别在绿熟期、转色期和成熟期气味最浓。随着果实成熟,挥发物质量浓度持续增加,气味更加浓郁。果色和成熟度对挥发物有显著影响。     

ASSESSMENT OF RIPENESS/DAMAGE IN BANANA (MUSA PARADISIACAL) BY ACOUSTIC RESONANCE SPECTROSCOPY

Acoustic resonance spectroscopy was used to assess ripeness of bananas at various stages of maturity. Two distinctly different varieties of bananas were selected for the study. Bananas were also bruised, and an acoustic response spectrum was taken before and after bruising. A dynamic impact force was applied to the base over which the fruit was kept horizontally with the help of a coupling agent. The output response was picked up by a hydrophone coupled, in turn to the base to the top (vertically opposite) of the fruit coupled. The signal was analyzed using Fast Fourier Transform. Response resonance frequencies decreased while damping ratio increased as the fruit ripened. Bruising of fruits resulted in decreased resonance frequency due to tissue damage. The values of resonance frequency and damping ratio could be correlated to the color changes due to ripeness of fruits as a result of either increased rates of respiration or external damage of tissue from mechanical or temperature abuse.     

沙枣果不同脱涩方法比较

采用35%乙醇溶液涂抹、蒸制、冷冻3种方法处理,对沙枣果的脱涩方法进行研究。测定时将沙枣果分成整果粉、果肉粉、皮粉和果核粉4个不同部位的样品,分别对未经处理和经过脱涩处理的整果中4个部位样品的单宁含量进行测定。结果表明：不同部位沙枣单宁含量不同,果肉粉中单宁含量最高,为8.670g/kg;其次是整果粉和皮粉分别为8.145、6.832g/kg;果核粉中单宁含量最低,为3.940g/kg;并且35%乙醇溶液涂抹对沙枣果的脱涩效果优于蒸制和冷冻两种处理。