FAILURE MECHANISMS OF TOMATO PERICARP TISSUE SUGGESTED BY LARGE AND SMALL DEFORMATION TESTS

Failure mechanisms of tomato pericarp tissue were investigated by measuring puncture and viscoelastic properties of tissue from fruit stored at 22C (nonchilled) or 5C (chilled) for 28 days, or at 5C for 15 days prior to transfer to 22C for an additional 13 days (prechilled) to facilitate ripening. The puncture properties of tissue remained unchanged during 28 days of chilling. However, tissue shear strength and rigidity increased with chilling, as demonstrated by increases in storage and loss moduli, and decreases in oscillatory strain and the loss tangent. Puncture failure force, failure firmness and storage and loss moduli of nonchilled and prechilled tissues decreased to low, constant levels by 12 and 9 days, respectively. Simultaneously, pseudoplastic and failure strains and oscillatory strain each increased. These data suggest that the loss of tissue compressive strengths and transition in the dominant mode of failure from cell relaxation and rupture to cell debonding occurred at a faster rate during ripening of prechilled (i.e., chill-injured) compared to nonchilled fruit.     

INFLUENCE OF THE SKIN ON PUNCTURE PROPERTIES OF CHILLED AND NONCHILLED TOMATO FRUIT

The puncture properties (firmness, toughness) of tomato skin and its influence on the overall puncture properties of mature-green fruit during ambient temperature (22C) ripening or chilled (5C) storage were estimated from the difference between whole fruit puncture force-deformation behaviour and that measured with the skin removed. Although the firmness of the skin of nonchilled fruit did not change significantly (p > 0.05) over 28 days of ripening, its contribution to overall puncture firmness increased from about 25 to 70%. Both skin toughness and its contribution to overall puncture toughness doubled within the first week of ripening of nonchilled fruit. The firmness of chilled fruit skin decreased (p > 0.05) only after 16 days of storage, but its contribution to overall puncture firmness remained constant at 25–30%. Both the toughness of the skin of chilled fruit and its contribution to overall puncture toughness remained constant during storage. Possible artifacts in the measurement of puncture properties of chilled fruit are discussed. The results are consistent with a toughening of tomato skin during early stages of ripening of nonchilled fruit that somewhat compensates for a rapid reduction in pericarp tissue integrity, and with an increase in firmness or rigidity of tomato skin and underlying tissue(s) during chilled storage of fruit.     

Chilling-Associated Softening of Tomato Fruit is Related to Increased Pectinmethylesterase Activity

Mature-green tomatoes chilled 15 days (5°C; RH >85%) were softer than nonchilled during subsequent ripening (22°C) by both whole fruit and pericarp tissue puncture (p<0.05), but not by flat-plate compression. No differences in total polygalactnronase (PG) or PG isozyme activity were evident although total activity was greater in nonchilled after 10 days ripening. Softening of nonchilled fruit correlated (p<0.05) with extracted PGI activity, while chilling-associated softening correlated (p<0.05) with higher initial extracted pectinmethylesterase (PME) activity. Extracted peroxidase remained constant throughout ripening but was greater (p<0.05) in pre-chilled fruit consistent with chill-induced membrane dysfunction. Transmission electron microscopy showed the middle lamella from pre-chilled tomatoes was swollen and less defined. Loss of turgor from translocation of water to the PME-modified cell wall was suggested to be responsible for softening as a consequence of chilling.     

EFFECT OF WAX APPLICATION ON THE QUALITY,LYCOPENE CONTENT AND CHILLING INJURY OF TOMATO FRUIT

ABSTRACT

Waxed and nonwaxed mature green tomato fruits were stored at 12C (nonchilled) or 5C (chilled) for 5, 10, 15 and 20 days before being transferred to 22C for 3, 6, 9 and 12 days, were evaluated for weight loss, chemical composition, skin color, chilling injury (CI) index and pigment content. Waxed fruits showed a delay in weight loss, color development and ripening. The sensitivity of tomato fruit to CI was reduced in waxed fruits, which showed a delay in the appearance of symptoms. A delay in chlorophyll degradation and lycopene synthesis was observed as a result of the use of wax and low temperature. Waxing of tomato fruits allowed their storage at temperatures below critical reducing CI sensitivity and maintaining quality giving more time for marketing.

PRACTICAL APPLICATIONS

Nowadays, local tomato producers use wax on fruits as an everyday practice to carry postharvest fungicides and to improve brightness. They store tomato fruits at nonchilling temperature (12C) because lower temperatures would cause chilling injury and irregular ripening. In this way, it is interesting that waxing tomato fruits allow reducing their storage temperature, protecting them from chilling injury and maintaining their quality and correct color change and ripening; thereby producers and sellers have more days to position their fruits with no extra cost.     

TOMATO PERICARP TISSUE RESONANCE AND ITS USE IN TEXTURE EVALUATION

The use of resonance properties, measured by dynamic oscillation using a constant stress rheometer, as textural parameters for excised pericarp tissue of tomato ( Lycopersicon esculentum Mill cv Trust) fruit during 21 days of ambient temperature ripening was assessed relative to the large-deformation behavior measured by flat-plate compression. The resonance frequency (f_r) of excised tissue discs decreased significantly (P < 0.05) over the first 9–12 days, and then approached a relatively low and constant value with subsequent ripening. A significant (P < 0.05) increase in associated resonance strain amplitude (y_max) became apparent after the first 9–12 days of tomato fruit ripening. Ripening-associated changes in bioyield and failure strengths, toughness, and apparent elastic and failure deformability moduli derived from flat-plate compression tests were similar to those observed for tissue f_r. Results were consistent with a change in the dominant mode of tissue failure from cell relaxation and rupture to debonding after 9–12 days of fruit ripening. A significant (P < 0.05) semilogarithmic relationship was observed between f_r, but not y_max, and compression parameters, allowing for reasonable prediction of large-deformation behavior on the basis of measurement of only f_r. The results demonstrate that resonance frequency may provide a useful parameter in the evaluation of tomato pericarp tissue texture.     

PRECONDITION OF 'D' ANJOU' PEARS FOR EARLY MARKETING BY ETHYLENE TREATMENT

'D' Anjou' pears (Pyrus communis, L.) harvested at an optimum maturity with the flesh firmness (FF) of 66.7N required 8 weeks of chilling at- 1C in order to initiate normal ripening in an ethylene-free environment at room temperature. If harvested fruit were not exposed to chilling or chilled at- 1C for less than 8 weeks, they could be preconditioned with 100 ppm ethylene for 3 days at 20C to initiate normal ripening. Fruit preconditioned with ethylene were capable of softening normally, reducing extractable juice, decreasing titratable acidity, and showing the climacteric rise of ethylene production during ripening at 20C when treated fruit had been further held at -1C in air for 14 days. The properly ripened fruit developed an acceptable dessert quality. When ‘d'Anjou’fruits had been stored at -1C in air for 8 weeks or longer, they could also be preconditioned without ethylene for 3 days at 20C to enhance ripening capacity. The nonethylene preconditioned fruit were capable of ripening normally following 14 days in simulated transit at -1C and upon arrival in retail markets at room temperature.     

Structural changes,chemical composition and antioxidant activity of cherry tomato fruits (cv. Micro‐Tom) stored under optimal and chilling conditions

BACKGROUND: Cherry tomato fruits cv. Micro‐Tom, a model plant for tomato genetics, were analysed in order to determine the main structural and chemical changes under optimal and chilling storage conditions. The comparison of Micro‐Tom to standard tomato cultivars will give an insight into suitability of this dwarf cultivar as a model for studying the influence of low‐temperature conditions on tomato fruits. RESULTS: During chilling, fruit tissue was progressively destroyed due to the collapse of the deep layers of the pericarp. Chilling lowered the typical tomato kinetics of ripening in sugars (glucose, fructose, sucrose), organic acids (tartaric, malic, citric, ascorbic and succinic) and the antioxidants phenol and lycopene, while carotenoid synthesis seemed to be blocked. Glutathione level was elevated and the activity of ROS scavenging enzymes was altered. Essentially, Micro‐Tom fruits showed a quality evolution that was similar to that described for standard tomato cultivars. CONCLUSION: The cherry tomato cultivar Micro‐Tom could be used as a model for studying the influence of low temperature on biochemical and structural changes taking place during chilling injury conditions. Copyright © 2009 Society of Chemical Industry     

ROLE OF CALCIUM AND CHELATING AGENTS IN REGULATING THE DEGRADATION OF TOMATO FRUIT TISSUE BY POLYGALACTURONASE

The effects of calcium ions and the chelating agents EDTA and citrate on the ability of partially-purified polygalacturonase (PG) from ripe tomato fruit to degrade polygalacturonate, preparations of isolated middle lamellae and cell walls (ML-CW), and outer pericarp tissue from tomatoes were examined. The inhibition of degradation by calcium ions was counteracted by the presence of EDTA or citrate, and these chelating agents also reduced the resistance to attack by PG on ML-CW and tomato pericarp tissue. Degradation by PG of ML-CW and pericarp tissue from all ripeness stages was stimulated by chelating agents. Susceptibility of fruit tissue containing the non-ripening (nor) gene to degradation by PG was similar to that shown by normal mature green fruit tissue. With increasing maturity of the mutant fruit, resistance to degradation declined, but not as rapidly as with normally ripening fruit. It appears that calcium associated with the ML-CW and its removal regulate the rate and extent of degradation by PG during normal tomato fruit ripening.     

Alleviation of chilling injury in postharvest tomato fruit by preconditioning with ultraviolet irradiation

BACKGROUND: Tomato fruit is usually stored at low temperatures for delayed ripening and extended shelf life. However, tomato fruit is susceptible to chilling injury when exposed to low temperatures. In this study, the potential effects of preconditioning with UV‐C or UV‐B irradiation on chilling injury of postharvest tomato fruit were investigated. RESULTS: Mature–green tomato fruit were exposed to 4 kJ m^?2 UV‐C or 20 kJ m^?2 UV‐B irradiation and stored for 20 days at 2 °C and subsequently 10 days at 20 °C. UV irradiation was effective in reducing chilling injury index and delaying ethylene peak. Furthermore, UV irradiation preserved storage quality as manifested by reduced weight loss, better retention of firmness, and higher contents of total soluble solids, soluble protein and soluble sugar during subsequent storage at 20 °C. UV‐C irradiation significantly delayed the development of the red colour after 10 days of storage at 20 °C. On the other hand, UV irradiation decreased total phenolics content and antioxidant capacity, suggesting possibly reduced stress response to low temperature resulted from enhanced physiological adaptation by UV preconditioning. CONCLUSION: Our results suggest that preconditioning with UV‐C or UV‐B irradiation in appropriate doses had a positive effect on alleviating chilling injury in postharvest tomato fruit. Copyright © 2012 Society of Chemical Industry     

CHILLING INJURY IN GREEN BANANA FRUIT: CHANGES IN PEROXIDASE ISOZYMES IN SOLUBLE AND PARTICULATE POOLS

Green banana fruit manifested severe chilling injury after 5–7 days storage at 5°C and 80% relative humidity. (Severe chilling injury is described here as a failure of the fruit to ripen on removal to conditions conducive to normal ripening.) The recoverable "wall bound" peroxidase fraction exhibited a sharp decline during this initial period of stress. Subsequent storage of severely chilled fruit at. 5°C resulted in a gradual increase in the "soluble" peroxidase pool and a rise in "wall bound" peroxidase to levels comparable to normal green fruit. After 30 days storage of fruit at 5°C the "soluble" and "wall bound" fractions of peroxidase peaked and declined rapidly in the latter pool. The increase in peroxidase of cold stressed fruit involved qualitative changes in isozyme species that differed from those isozymes which emerge during normal fruit ripening. It is suggested that the initial decrease in "wall bound" peroxidase results in a loss in capability of the tissue to adapt to low temperature stress. The belated increase in peroxidase activity may be associated with a typical "cold hardening" response which develops only after an irreversible or "plastic strain" damage has occurred     

Modelling of rheological characteristics of various spaghetti types

Spaghetti enriched with resistant starch was produced to increase the dietary fibre intake of consumers. In the product base it was compared to bran and control spaghetti regarding to viscoelastic properties. Viscoelastic properties were tested by relaxation and creep tests by using TA-XT2i texture analyser. The viscoelastic properties gave structural information. Relaxation and creep data were analysed by generalized Maxwell (two- and three-termed), Peleg & Normand, Burgers and Peleg models, respectively. For relaxation three-termed Maxwell and for creep behaviour Burgers model represented viscoelastic behaviour satisfactorily. In general, bran spaghetti was found to have the lowest elasticity. All the samples started to loose their elasticity as cooking time proceeded and it became easy to deform them. Instrumentally, spaghetti with resistant starch was found to be better than bran enriched spaghetti.     

Increased ethylene biosynthesis elevates incidence of chilling injury in cold‐stored ‘Amber Jewel’ Japanese plum (Prunus salicina Lindl.) during fruit ripening

Mature ‘Amber Jewel’ Japanese plum fruit were stored at 0 or 5 °C for 3 and 6 weeks to investigate their effects on ethylene (C₂H₄) biosynthesis during ripening at ambient temperature in the development of chilling injury (CI) and fruit quality. CI (internal breakdown and browning) and fruit softening were higher during ripening, in the fruit stored at 5 °C than 0 °C, irrespective of storage period (SP). C₂H₄ production and activities of 1‐aminocyclopropane‐1‐carboxylic acid synthase (ACS) and 1‐aminocyclopropane‐1‐carboxylic acid oxidase (ACO) enzymes, and 1‐aminocyclopropane‐1‐carboxylic acid (ACC) content were higher during ripening in fruit stored at 5 °C than 0 °C. The fruit stored at 5 °C also exhibited higher respiration rate and higher soluble solids concentration/titratable acidity ratio. In conclusion, increase in storage temperature and SP elevates the activities of ACS and ACO enzymes and consequently C₂H₄ production which leads to the development of CI in plum fruit with advancement of ripening.     

Ripening tomato fruit after chilling storage alters protein turnover

BACKGROUND: Tomato fruit is of prime importance owing to its qualities for human nutrition and its economic value. In order to extend its commercial life, it is harvested at mature but unripe stages and stored at low temperatures. The goal of this work was to study the influence of harvest and chilling storage of mature green tomato fruit (cv. Micro‐Tom) on the protein pattern, amino acid content and protease activity during fruit ripening. RESULTS: Fruits were sampled during ripening in three different conditions: 1, on the vine; 2, off the vine; 3, off the vine after 4 weeks at 4 °C. During all fruit ripening conditions, protein level decreased while amino acid content increased. Chilling storage of mature green fruit led to a reduction in protein content. Ripening off the vine (conditions 2 and 3) resulted in a threefold increase in red fruit amino acid levels when compared with red fruit on the vine. Protease activities (autoproteolytic, azocaseinolytic and gelatinolytic) were detected in all fruits evaluated and were differently affected by ripening stage, ripening conditions and the presence of specific inhibitors. CONCLUSION: Harvest and chilling storage increased endogenous substrate proteolysis, azocaseinolytic activity and free amino acid levels, which could be related to fruit quality. Copyright © 2011 Society of Chemical Industry     

PROPERTIES OF IAA OXIDASE FROM RIPENING TOMATO FRUIT

An indoleacetic acid (IAA) oxidizing enzyme was isolated from the pericarp of ripening tomato fruit by column chromatography fractionation. IAA oxidase from extracts of tomato pericarp exists in a high molecular weight form (>200,000) or in a low molecular weight form (∼40,000) or both depending upon extraction procedures. When IAA was oxidized by the high molecular weight form of IAA oxidase, a relatively long lag time was observed. The low molecular weight form of IAA oxidase activity showed no lag or a very short, 1- to 2-minute lag period. Enzyme activity was optimal at pH 6.1 and was stimulated by 2,4-dichlorophenol (DCP) and MnCl_2. Neither 3-methyleneoxindole nor indolealdehyde were found as a major IAA oxidation products. Moderate increase in activity of IAA oxidase activity was observed during ripening of tomato fruit.     

Characterization of the Red Layer and Pericarp of Processing Tomato using Magnetic Resonance Imaging

Abstract: The characteristics of tomato pericarp are closely associated with peelabililty, an important quality attribute of processing tomatoes. Different types of tissue exist in the pericarp of tomato. The outermost region of the pericarp, the red layer, is removed with the skin during peeling. This study investigated the morphological features and tissue properties of red layer and pericarp for 3 processing tomato cultivars using magnetic resonance imaging (MRI). The red layer can be visualized in MR images with T₂ weighting, indicating the red layer has different properties compared to the rest of the pericarp region. Tomatoes were imaged with a set of MRI sequences with signal intensity dependent on different water proton properties. Principal component analysis (PCA) of the statistical features revealed clustering of fruit by cultivar. The spatial distribution of cultivars in the PCA score plot followed their rank of peeling performance. MRI demonstrated potential as a nondestructive method to characterize tomato pericarp and evaluate the peelability of processing tomatoes. Practical Application: Peelability of tomatoes affects the quality of value‐added whole peel and diced tomato products. The properties of the pericarp of tomato are directly related to the peelability of tomatoes. MRI provided a fast and nondestructive method to characterize the properties of tomato pericarp. The result of this work gives insight into the correlation between tomato pericarp characteristics and peelability.     

Nondestructive Measurement of Peel Gloss and Roughness to Determine Tomato Fruit Ripening and Chilling Injury

Mature-green tomatoes showed a gradual decrease in peel gloss during ripening at 20°C. Gloss correlated well with parameters such as a* values and °Brix and could possibly serve as criteria for ripeness. When stored at 2°C for 7, 14 or 21 days and then allowed to ripen at 20°C, fluctuations in gloss during ripening were observed. Peel roughness increased as a result of chilling, but did not appear to be related to time elapsed at the chilling temperature and no changes were observed on subsequent ripening. Pink tomatoes showed fluctuations in gloss similar to mature-green fruit. Chilling had no influence on roughness of pink tomatoes.     

Postharvest quality of arazá fruit during low temperature storage

Arazá (Eugenia stipitata Mc Vaugh) fruits at breaker stage of maturity were stored at 7, 10, 12, or 20 °C and 85-90% RH for 2 weeks, with or without an additional simulated shelf-life period (3 days at 20 °C and 70% RH). Some half-yellow (turning) arazá fruit were also stored at 7 or 12 °C. Respiration rate, ethylene production, quality traits and physiological disorders and decay were monitored. Arazá fruit of both stages of maturity showed a climacteric pattern of ripening, with the maximum levels of respiration being reached after 5 days at 20 °C for breaker fruit, while half-yellow fruit ripened totally after one day. Weight loss was the most limiting quality trait for arazá fruit. Chilling injury symptoms included skin scald (only at 7 °C), uneven ripening (at 7 or 10 °C, including uneven softening during storage, particularly in breaker fruit), and slight acidification at 7 °C. Decay in the post-storage shelf-life periods (mainly Gloesporium sp.) was particularly high after storage at 7 °C in breaker fruit. The storage of breaker arazá fruit at 12 °C is recommended because this prevents chilling injury and flesh acidification, and allows normal fruit ripening during a post-storage shelf-life at 20 °C, as revealed by the lower organic acids (mainly malic) content and increased sugar (glucose, fructose and sucrose) content.     

THE EFFECTS OF TURGOR PRESSURE ON PUNCTURE AND VISCOELASTIC PROPERTIES OF TOMATO TISSUE

The effects of turgor pressure on puncture and viscoelastic properties of mature-green tomato pericarp were examined using tissue discs soaked in a range of osmotica (0.0–0.6 M mannitol) for at least 36 h at 4C. Turgor pressure was estimated from the osmotic potential of soaking solutions that induced incipient plasmolysis. Based on volume changes, the osmotic potential and turgor pressure of fresh tissue were estimated to be −0.56 ± 0.08 MPa and 0.20 MPa, respectively. However, puncture and viscoelastic properties corresponded to a turgor pressure of 0.15 MPa. The discrepancy between calculated and actual turgor pressures was attributed to the presence of apoplastic solutes. The data from this study revealed a general increase in cell wall stress, strain and elasticity with increasing turgor. With increases in turgor above that of untreated tissue both wall extensibility and elasticity became limiting and thus cell wall stiffness increased. Conversely, a decrease in turgor below that of untreated tissue led to an increase in viscoelasticity. Increases in bioyield and pseudoplastic bioyield strains with a variation in turgor from that of untreated tissue were consistent with cell debonding as a dominant mechanism of tomato tissue bioyielding. The reduced failure force, deformation and firmness with increasing turgor were consistent with cell rupture as a predominant mechanism of failure of mature-green tomato pericarp tissue.     

Viscoelastic characterization of solid foods from creep compliance data: application to potato tissues

 Two software systems were developed to simplify acquisition and analysis of data describing creep behavior of viscoelastic solid foods and to determine the magnitude of instantaneous elastic compliance, viscoelastic compliances and viscosity associated with Newtonian flow. The first of these systems was used to store information on the experiment, to collect the data generated during the experiment, to present these in real time and to create files containing the experimental data for subsequent analysis. The second system was used to fit data to discrete Kelvin-Voigt models with four, six or eight constants. The systems were tested in the calculation of rheological properties of fresh and cooked potato tissues. A six-element Burgers model containing two discrete Voigt units proved the most suitable for defining tissue creep behavior, suggesting that different structural components could be related to each unit. The instantaneous elastic modulus could be associated with internal cell pressure. Gelatinization of starch and viscoelastic units appeared to reflect the viscoelastic properties of pectic substances and hemicelluloses, respectively. Received: 5 March 1998     

1-MCP及其结构相似物处理对番茄采后贮藏效果的影响

为了研究环丙烯类乙烯抑制剂的作用效果,以绿熟期番茄为试材,用1-甲基环丙烯(1-MCP)、1-戊基环丙烯(1-PentCP)、1-辛基环丙烯(1-OCP)处理后,常温(18℃±2℃)贮藏,每隔3 d测定1次理化指标,研究三者对番茄果实后熟衰老和贮藏效果的影响。结果表明:1-MCP及其结构相似物处理番茄不同程度地降低了呼吸强度和乙烯释放量的峰值,抑制了番茄果实硬度的下降,延缓了可溶性固形物含量的上升,同时也有效抑制了后熟期番茄果实过氧化氢酶(CAT)活性、过氧化物酶(POD)活性,延缓了果实的后熟衰老。3种试验的抑制剂中,1-MCP、1-PentCP和1-OCP处理随支链长度的增加,抑制后熟衰老的效果依次降低。