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Pectin solubility in ripening tomato fruit is typically studied in vitro, employing isolated cell walls; however, it is unknown whether in vitro studies address the actual changes in the status of pectins in the fruit in situ. In vivo pectin solubilization was examined in a pressure-extracted apoplastic fluid obtained from ripening and chill-injured tomato fruit with down-regulated polygalacturonase (PG) activity and untransformed wild-type. Pectin levels in apoplastic fluid increased 3-fold during ripening and were not affected by PG levels. In contrast, PG strongly affected pectin levels in bulk, enzymically active pericarp fluid. There was a 14-fold increase in bulk pectin levels during ripening of PG-antisense fruit and a 36-fold increase in wild-type fruit. Pectin levels in the apoplastic fluid of fruit stored at 5 °C for 14 days were 40% lower than that of freshly harvested mature-green fruit, but increased significantly upon transfer of fruit to 15 °C. Monomeric galactose in the apoplastic fluid increased from 41 mg·mL^–1 at the mature-green stage to 67 mg·mL^–1 in ripe fruit. Bulk levels of galactose were 3- to 4-fold higher than apoplastic levels. After low-temperature storage galactose levels were 50% and 20% lower than in freshly harvested fruit for the bulk and apoplastic fluids, respectively. These results indicate that in vivo pectin solubilization is restricted and largely independent of PG. Low-temperature storage reduces in vivo pectin solubilization, an effect that is reversed upon transfer of fruit to higher temperature following cold storage.

Chilling injury limits the postharvest handling of many fruit and vegetables. In low-temperature storage trials, control treatments typically consist of fruit stored above the injury threshold. Since chilling exposures for tomato fruit often exceed 2 weeks, controls stored above the threshold continue to ripen, confounding comparisons with fruit maintained at low temperatures. In this study, the ethylene action inhibitor 1-MCP was used to arrest ripening to permit more valid comparisons between fruit stored under the two temperature regimes. Mature-green tomatoes were treated with EthylBloc and then stored at 5 or 15 °C for 2 or 3 weeks after which time the fruit stored at 5 °C were transferred to 15 °C to allow the expression of injury symptoms. 1-MCP inhibited ripening of fruit stored at 15 °C for 2 to 3 weeks. Color, pericarp firmness, and pectin solubilization of MCP-treated fruit stored at 15 °C remained at the values of mature-green fruit, validating their use as controls for these physiological characteristics. After 2 to 3 weeks at 15 °C, MCP-treated fruit resumed normal ripening. Comparing the fruit removed from low-temperature storage with nonripening controls at 15 °C revealed that storage at 5 °C for 2 to 3 weeks decreased the hue (yellowing) but did not affect chroma or lightness, maintained firmness, and did not affect pectin metabolism. Electrolyte leakage increased or remained unaffected by cold storage. MCP-treated fruit had slightly higher electrolyte leakage than non-MCP-treated fruit after storage at either 5 or 15 °C. We conclude that MCP-treated fruit provide adequate controls in experiments designed to study many aspects of low-temperature storage.

‘Hayward’ kiwifruit were treated with 0.5 μL·L⁻¹ of 1-methylcyclopropene (1-MCP) and stored in air at 0 °C. Treatment with 1-MCP reduced softening of kiwifruit during storage but did not affect soluble solids or titratable acidity. Sensory analyses were performed by a consumer panel and by trained panelists after 41, 77, and 161 days in storage. 1-MCP treatment negatively affected consumer preference, expressed as degree of liking. The trained panel clearly perceived 1-MCP-treated kiwifruit after 41 days in storage at 0 °C as more sour and firmer but less juicy, less sweet, and less flavorful than untreated fruit. After 161 days in storage, the perceived differences between 1-MCP-treated and untreated fruit had been reduced for sweetness and acidity, but the panel perceived 1-MCP-treated fruit as firmer and lagging behind in the ripening process. Altering the poststorage ripening rate, by placing 1-MCP-treated fruit at a higher temperature than untreated controls, allowed fruit to develop in such a way that a sensory panel was unable to distinguish between treatments. This result indicates that 1-MCP-treated fruit can be perceived by the consumer as similar to untreated fruit if adequately conditioned.

The respiratory behavior of fresh-cut melon under modified atmosphere packaging at various temperatures was characterized to assess the potential for shelf life extension through low-oxygen and to generate information for the development of appropriate packaging conditions. Cantaloupe melon (Cucumis melo var. cantalupensis ‘Olympic Gold’) cubes were packaged and stored at 0, 5, 10, and 15 °C. Packages attained gas equilibrium after 5 days at 10 °C, 6 days at 5 °C, and 10 days at 0 °C. In cubes stored at 15 °C, decay started before steady-state gas levels were reached. Respiration rates were measured and respiratory quotient calculated once steady-state O₂ and CO₂ partial pressures were achieved inside the packages. O₂ uptake increased with temperature and O₂ partial pressure (pO_{2 pkg}), according to a Michaelis-Menten kinetics described by = [( × pO_{2 pkg})/( + pO_{2 pkg})]. Respiratory parameters were modeled as an exponential function of temperature: = {[1.34 × 10⁻¹⁷ × e^{(0.131 × T)} × pO_{2 pkg}]/[1.15 × 10⁻²⁴ × e^{(0.193 × T)} + pO_{2 pkg}]} (R ² = 0.95), Q ₁₀ = 3.7, and E_a = 84 kJ·mol⁻¹. A good fit to the experimental data was also obtained considering as constant: R_O2 = {[4.36 × 10⁻¹⁴ × e^{(0.102 × T)} × pO_{2 pkg}]/[0.358 + pO_{2 pkg}]} (R ² = 0.93), Q ₁₀ = 2.8, and E_a = 66 kJ·mol⁻¹. These results provide fundamental information to predict package permeability and steady-state pO_{2 pkg} required to prevent anaerobic conditions and maximize shelf life of fresh-cut cantaloupe. The kinetics of respiration as a function of pO₂ suggests that no significant reductions in respiration rate of fresh-cut cantaloupe can be achieved by lowering O₂ levels.