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.     

TOMATO POLYGALACTURONASE EXTRACTABILITY

The extractability of polygalacturonase (PG) activity from alcohol-insoluble solids (AIS) prepared from red-ripe tomato pericarp tissue was investigated using acetate (pH 4.5), citrate (pH 4.5) and MES (pH 6.0) buffers. The acetate buffer was also investigated with increasing concentrations of NaCl, CaCl₂, MgCl₂, ethylenediaminetetraacetic acid (EDTA) or ethyleneglycol-bis(β-aminoethylether)-N,N'-tetraacetic acid (EGTA). Heat treatment of AIS to prepare control material suppressed PG extractability but not in situ PG activity, as evidenced by the release of significant quantities of soluble uronides into extraction media. With only a single extraction, acetate buffer containing > 1 M NaCl yielded the greatest amount of PG activity (> 50% of maximum extractability), with MES buffer being only marginally less efficient. However, 3 successive extractions over a 2 h period yielded significantly greater amounts of PG activity. The greatest yields of PG activity were obtained by successive extraction with parent MES and acetate buffers. There appeared to be little benefit in adding NaCl or a chelating agent to the extraction medium. Use of these extractants is suggested to have led to losses of PG activity during dialysis, via coprecipitation of PG protein with otherwise soluble uronide material that was released in greater quantities when these extractants were used. Increasing CaCl₂ and MgCl₂ concentrations reduced the amount of extracted PG activity similarly, to about 50% of maximum levels with successive extractions.     

INFLUENCE OF ATMOSPHERIC OXYGEN AND OZONE ON RIPENING INDICES OF NORMAL (Rin) AND RIPENING INHIBITED (rin) TOMATO CULTIVARS1

ABSTRACT Ethylene (10ppm) dependent mediation of normal and mutant (rin) tomato fruit ripening was promoted by 100%oxygen, 3.7 pphm ozone, or their combination. All ripening indices studied (respiration, chlorophyll degradation, carotenoid accumulation, softening, and aroma development) were promoted by oxygen and/or ozone. Ozone also acted independent of ethylene in promoting chlorophyll degradation and aroma development in normal fruit, but did not appreciably affect these quality attributes in mutant fruit. Lycopene accumulation in normal and mutant fruit and aroma formation in normal fruit were promoted to a greater extent by ozone than were other ripening indices. Mutant (rin) fruit contained 27% of the lycopene that was present in normal (Rin) fruit after ripening in O₂ containing 10ppm ethylene and 3.7 pphm ozone, whereas they contained only 3%of the lycopene in normal fruit after ripening in air containing 10ppm ethylene.     

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.     

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.     

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.     

Influence of EDTA and citrate on thermal stability of whey protein stabilized oil-in-water emulsions containing calcium chloride

The influence of calcium ions and chelating agents on the thermal stability of model nutritional beverages was examined. Oil-in-water emulsions (6.94% (w/v) soybean oil, 0.35% (w/v) WPI, 0.02% (w/v) sodium azide, 20 mM Tris buffer, 0–10 mM CaCl₂, and 0–40 mM EDTA or citrate, pH 7.0) were stored at temperatures between 30 and 120 °C for 15 min. The particle size, particle charge, creaming stability, rheology, and free-calcium concentration of the emulsions were then measured. In the absence of chelating agents, appreciable droplet aggregation occurred in emulsions held at temperatures from 80 to 120 °C, which led to increased emulsion particle diameter, shear-thinning behavior, apparent viscosity, and creaming instability. Addition of chelating agents to the emulsions prior to heating decreased, but did not prevent, droplet aggregation in the emulsions. EDTA was more effective than citrate in decreasing droplet aggregation. Heat treatment increased the amount of chelating agents required to prevent droplet aggregation in the emulsions. Free-calcium concentration and droplet surface potential was independent of heat-treatment temperature, indicating that the performance of the chelating agents in binding calcium ions was not affected by the heat treatment. It was suggested that increased hydrophobic attractive interactions between the droplets occurred during heating, which induced droplet aggregation.     

Protein and enzyme changes in tomato fruit in relation to blotchy ripening and potassium nutrition.

The effects of potasium deficiency and blotchy ripening in tomato fruit on some nitrogenous constituents, especially the proteins, have been investigated. The distribution of nitrogen in normal and potassium-deficient fruit of the cherry tomato Lycopersicon pimpinellifolium was examined and compared with that from potassiumdeficient and blotchy ripened fruit of a cultivated variety (L. esculentum, cv. Moneymaker). The protein fraction from cv. Amberley Cross was analysed in detail using disc gel electrophoresis. Changes induced by potassium deficiency in the general protein pattern and on a wide range of enzymes active in ripening were compared with the effects brought about by blotchy ripening. The distribution of protein components and isoenzymes in low potassium fruit was to a large extent similar to that of normal tissue at an earlier stage of development, whereas the alterations in blotchy tissue appeared to be of a random nature.     

Mechanical and optical assessment of the ripening of tomato fruit with reduced polygalacturonase activity

The ripening characteristics of modified tomatoes (Lycopersicon esculentum Mill cv Ailsa Craig), which express antisense RNA to polygalacturonase (PG) and thus have very low activity of this enzyme, were compared with control fruit. Previous studies of these fruits showed that although PG activity was reduced to approximately 1% of that in untransformed tomatoes, this reduction had no effect on softening. Further detailed mechanical assessments have now been performed which revealed small, but significant differences in the fruit ripening characteristics between control and antisense fruits. Compression along the polar axis of the PG antisense fruit was significantly reduced relative to the control. Deformation at failure (h), ‘modulus’ (M), coefficient of compression (K_c), and coefficient of shear (K_s) values from probe tests along the equatorial axis also indicated that the antisense fruit was firmer. Although these significant differences in texture properties were observed between the antisense fruit and the control, they were quite limited in extent, as compared to the normal evolution observed during ripening. Scanning electron microscope studies on the sub-exocarpic region of the pericarp showed that cell wall separation was reduced in the ripe antisense tomatoes, and this may explain the change in mechanical properties. Optical measurements made with both Hunter Color Difference (Hunter Lab Ltd, Fairfax. VA, USA) and Micromatch 2000 (ICS Texicon Ltd. Altrincham, UK) spectrophotometer systems showed that the ‘a’ (green/red) component of colour of the antisense tomatoes was increased relative to that of the control samples. The effect of PG on softening and of cell wall breakdown on mechanical and optical properties is also considered.     

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.     

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.     

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.     

Yeast flocculation: Calcium specificity

Expression of flocculation in yeast requires the presence of multi-charged cations. Calcium ions fulfil this role over a broad pH range. At near neutral pH, magnesium and a variety of transition elements can induce flocculation. Calcium-induced flocculation was competitively inhibited by excess sodium ions whereas magnesium-induced flocculation was not competitively inhibited. Potassium and lithium ions caused similar inhibition but to a lesser extent. ⁴⁵Ca effux from yeast cells was greatly increased by the external presence of buffer and cations. Inhibition of flocculation by chelating agents, EDTA or EGTA, was overcome by excess calcium ions. Flocculation could not be induced, under these conditions, by excess magnesium or transition-element salts. It was concluded that yeast flocculation has a direct specific requirement for calcium ions. Other ions cause flocculation indirectly by effecting calcium ion leakage from cells, which is then able to initiate flocculation. Low calcium concentrations were susceptible to competitive inhibition by sodium ions present in most acidic buffers. In addition, citrate ions inhibited flocculation, probably by sequestration of leaked calcium. Flocculation by salts, other than calcium, was thus restricted to a neutral or high pH range.     

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.     

Purification and changes in activities of tomato pectinesterase isoenzymes

Changes in the isoenzymes of pectinesterase were studied during the development of normal tomato fruit and of fruit from two near isogenic lines containing the ‘Never ripe’ (Nr) and ‘ripening inhibitor’ (rin) alleles. Nr fruit ripen slowly to an orange-red while rin is even more extreme, eventually turning yellow. Enzyme activity present in normal green fruit increases during ripening, as did that in Nr fruit. No comparable increase was observed in rin fruit. Pectinesterase activity was resolved into two major forms by ion-exchange chromatography. One of these isoenzymes (PE 2) accumulated during the ripening of normal and Nr fruit, but did not change in the rin fruit. PE 2 was purified to homogeneity, judged by electrophoresis in dodecyl sulphate-polyacrylamide gels.     

多聚半乳糖醛酸酶(PG)反义基因对加工番茄果实成熟的影响

采用农杆茵(agrobacterium tumefaciens)介导法将多聚半乳糖醛酸酶(PG)反义基因导入新疆加工番茄(lycopersicon esculentum,品种代号98-75)。通过卡那霉素抗性筛选获得10株转化植株,PCR和Southern blot分析表明,其中4株为阳性植株,反义PG基因已整合到这4株加工番茄基因组中。转基因加工番茄的硬度和可溶性固形物含量高于同期对照果实;果实饱满有光泽;此4株转基因番茄果实的PG活性分别为对照番茄果实的83％、88％、63％和46％;脂氧合酶(LOX)活性下降;可溶性果胶含量在同期低于对照。Northem blot分析表明,转基因番茄果实的PG、LOX和LeEXPl基因表达水平下降。研究结果表明,转反义PG基因加工番茄果实成熟软化进程被延缓,果实品质有一定改善。     

CAN WE PREDICT PEELING PERFORMANCE OF PROCESSING TOMATOES?

Tomato processors are increasingly interested in being able to predict whether tomatoes will peel well, and therefore, yield high‐value processed tomatoes. We describe two statistical models for peeling applied to multiple years of data. One model is appropriate for perfect or defect‐free tomatoes, and the second model is valid for the normal population of tomatoes obtained following mechanical harvesting. The ability to peel perfect tomatoes was significantly affected by exposure of tomatoes to temperatures greater than 100F, by fruit weight and by pericarp wall thickness. The peelability of a normal population of tomatoes was influenced by tomato weight and width as well as degree‐days and exposure to temperatures greater than 90F. Thickness of the pericarp walls and red layer positively affected the peelability of normal tomatoes. The ability to predict tomato peelability using statistical models may improve the quality of processed tomatoes and may result in more efficient commercial peeling operations.     

AREA- AND PERIMETER-DEPENDENT PROPERTIES AND FAILURE OF MATURE-GREEN AND RED-RIPE TOMATO PERICARP TISSUE

The influence of tomato fruit ripeness on area- and perimeter-dependent properties and dominant failure mechanisms of pericarp tissue were investigated. Tissue discs from mature-green and red-ripe fruit were punctured with a flat-ended cylindrical probe and compressed with a flat plate at a constant rate of deformation. Approximately linear force-deformation curves were obtained to tissue failure by both puncture and flat plate compression, interrupted by a region of pseudoplastic deformation at a relatively low initial bioyield force. Based on estimated area- and perimeter-dependent coefficients and firmness (force/deformation) values, initial bioyielding of tissue appeared to be associated with an abrupt increase in cell-to-cell compaction. Puncture of mature-green tissue led to premature failure induced by shearing or rupture of tissue at the probe perimeter. The contribution to puncture of perimeter-dependent or shear-associated forces and a putative "zone of influence" increased markedly with ripening, while the contribution of area-dependent or compression associated forces generally decreased. A concomitant decrease in failure force and firmness with ripening reflected a general loss of both tissue compression and shear strengths. These results suggested that the dominant mode of tissue failure changed with ripening, from cell relaxation and rupture to cell debonding. The data obtained in this study emphasize the need to exercise caution in the interpretation of force-deformation parameters derived from puncture tests alone.     

Effect of the introduction of non-ripening mutant genes on the composition and enzyme content of tomato fruit

The genes Never ripe (Nr) and ripening inhibitor (rin) were introduced by backcross programmes into the tomato variety Ailsa Craig to give nearly isogenic lines. The effect of each of these genes on the major constituents of fully-developed tomato fruit has been studied as part of a programme to select breeding lines bearing fruit having prolonged shelf-life. The Nr gene produced high acid, low sugar, slow-ripening tomatoes that were very firm. Because of the adverse effect of this gene on tomato composition, even in heterozygous form, it has little or no commercial potential. The rin gene also led to the production of poor quality fruit. The heterozygote (Rin rin) gave fruit that were similar in compositon to that of the recurrent line, but despite possessing lower polygalacturonase activity were not significantly firmer. The distribution of isoenzymes in the normal and mutant tomato tissues was examined by gel electrophoresis. The majority of the enzymes investigated showed a diminished activity in Nr and rin fruit compared with normal. The very low activities of polygalacturonase, phosphofructokinase and NADP⁺-malic enzyme in the fully-developed mutant lines offers an explanation for the weak climacteric respiration rise and slow ripening of Nr fruit and the non-climacteric behaviour of rin fruit.     

DIFFERENCES IN THE RATE OF COLORATION IN TOMATO FRUIT

The evolution of fruit color of twelve tomato (Lycopersicon esculentum Mill.) cultivars during ripening was evaluated. Final color of each of the cultivars was determined by calculating its fresh tomato color index (TCI_f). Luminosity (L*), red-green component (a*), a*/b* ratio, hue angle (h*), dominant wavelength (DW) and fresh tomato color index (TCI_f) were the parameters that best differentiated the ripening stages of tomato fruit. Dominant wavelength and purity of excitation were correlated with a* and b*. Fresh tomato color index (TCI_f) was related to the luminosity (L*) and yellow-blue component (b*).