Commercialization of 1-methylcyclopropene (1-MCP) has provided a new tool to storage operators for management of fruit quality in the postharvest environment. For apple as an example, availability of the commercial 1-MCP product SmartFresh has brought an additional dimension to decisions regarding postharvest chemical treatments, storage temperature regimes, storage atmospheres, and planned storage duration based on fruit maturity at harvest. Poststorage impacts of 1-MCP use at harvest on handling and packing procedures have also become apparent with commercial use. Marketing programs have also been impacted because the “tails of the manifest” (large/small sizes, lower color grades) can be held longer in cold storage after packing primarily as a result of slower loss of firmness in many cultivars. Although some quality issues, primarily related to physiological disorders occurring on specific cultivars, are yet to be fully resolved, continuing widespread use of 1-MCP is indicative of its commercial usefulness.
Ripening and development of physiological disorders and decay were assessed in ‘d’Anjou’ pear fruit after 1-methylcyclopropene (1-MCP) treatment and cold storage in air or controlled atmosphere (CA). Fruit were exposed after harvest to 0 or 12.6 μmol·L−1 1-MCP and then stored at 0.5 °C in air or 1, 3, or 5 kPa O2 with 0.5 kPa CO2. Pears were held poststorage at 20 °C for 7 days before analysis. 1-MCP fruit usually had higher hue compared with controls. Softening after removal from storage was delayed in 1-MCP fruit regardless of storage atmosphere; however, control fruit stored in air or CA ripened to below 23 N, a minimum value for consumer acceptance, after all storage durations. 1-MCP fruit stored in air, 3, or 5 kPa O2 softened in the outer cortex (fruit surface to 8 mm into the cortex) to below 23 N only after 9 m, however, only fruit stored in air softened to less than 23 N in the inner cortex (8 mm to coreline). 1-MCP treatment also delayed deformation in cortex tissue tensile strength (TTS); after six or more months, 1-MCP fruit TTS was lower compared with those for control fruit. After 9 m, 1-MCP fruit stored in air had TTS values similar to those of controls whereas values for fruit stored in CA increased with CA O2 concentration. Titratable acidity was higher in 1-MCP-treated fruit stored in air (6 m only) or 3 or 5 kPa O2 compared with controls. Superficial scald developed after 6 m on control fruit stored in air or 5 kPa O2 and on control CA fruit regardless of O2 concentration after 9 m. No 1-MCP fruit developed scald. The results indicate ‘d’Anjou’ pear ripening in response to 1-MCP is influenced by storage pO2 as well as storage duration, and at the 1-MCP treatment concentration used, softening to a consumer standard for firmness occurred only in fruit cold stored in air for 9 months plus a 7-day poststorage ripening period. These fruit had peel hue less than 100, and the yellow peel color may not be consistent with current market expectations.
`Golden Delicious' apple [Malus sylvestris var. domestica (Borkh.)] cortex disks suspended in solutions containing a nitric oxide (•NO) donor [S-nitrosoglutathione (GSNO) or sodium nitroprusside (SNP)], •NO gas, or nitrite (KNO2) were used to identify impacts of •NO on ethylene production and NO2– on •NO and ethylene production. Treatment with GSNO or SNP reduced ethylene biosynthesis compared with control treatments containing equimolar concentrations of oxidized glutathione (GSSG) or Na4(CN)6 respectively. Apple disk exposure to •NO gas did not impact ethylene production. Treatment with NO2– resulted in increased •NO production and decreased ethylene biosynthesis. Generation of •NO increased linearly whereas ethylene generation decreased exponentially with increasing NO2– treatment concentration. •NO was enhanced in autoclaved tissue disks treated with NO2–, suggesting that its production is produced at least in part by nonenzymatic means. Although this evidence shows •NO is readily generated in apple fruit disks by NO2– treatment, and ethylene synthesis is reduced by •NO/NO2– generated in solution, the exact nature of •NO generation from NO2– and ethylene synthesis modulation in apple fruit disks remains to be elucidated.
Airborne methyl jasmonate (MJ) can modulate apple fruit ripening, including the degreening process. Degreening of `Fuji' and `Golden Delicious' apples by jasmonates [jasmonic acid (JA) and MJ] in aqueous solution was investigated. JA and MJ applied by dipping apples in solutions of jasmonates for 2 min enhanced degreening during ripening at 20C. MJ was more effective at promoting degreening compared to JA. The minimum concentration of jasmonates required to promote significant degreening during the 2-week ripening period was 1 mM. Degreening of jasmonate-treated apples ripened at 4C progressed slower compared to apples ripened at 20°C. JA stimulated apple fruit ethylene production at concentrations as low as 10 μM. Jasmonates at 1 or 10 mM were more effective at accelerating the degreening process compared to 0.35 or 3.5 mM ethephon. Firmness, soluble solids content, and titratable acidity of `Fuji' apples were not significantly affected by jasmonate treatments. Peel injury occurred on apples treated with 10 mM JA or 3.5 mM ethephon.
Jasmonic acid and its methyl ester (methyl jasmonate), regarded as putative plant growth regulators, are naturally occurring in higher plants and present in a variety of plant organs including apple fruit. Pre- and post-climacteric `Summer Red' apples were exposed for 12 hrs to a low concentration (25ul/4L) of atmospheric methyl jasmonate. Ethylene and volatile production were measured with GC/MS at harvest and through 15 days at 20°C after treatment. Forty eight headspace volatile compounds were identified and quantified. Results showed that methyl jasmonate effects depended on stage of fruit development. Methyl jasmonate stimulated ethylene, ester, alcohol, and acid productions in preclimacteric fruits while no significant effects were observed on postclimacteric fruits. Ketone and aldehyde volatile evolutions were not significantly affected by methyl jasmonate regardless of harvest date.
Enclosing `Fuji' apple (Malus ×domestica Borkh.) fruit in paper bags 2 months after full bloom delayed the increase in internal ethylene concentration at the onset of fruit ripening, and increased the respiration rate early in the bagging period. Bagging delayed and reduced red color development, especially on the blush side, but did not affect fruit resistance to gas diffusion. External surface color changed significantly within the first 4 days after bags were removed. Exclusion of UV-B from sunlight by Mylar film after paper bag removal impaired red color development. Bagging during fruit development increased superficial scald but eliminated stain during cold storage. Exposure to sunlight for 19 or 20 days before harvest reduced scald incidence in comparison with leaving bags on until harvest.
Climacteric `Fuji' apples (Malus ×domestica Borkh.) were treated with water, 0.45 mmol·m–3 1-methylcyclopropene (MCP), 2 mmol·L–1 methyl jasmonate (MJ), or both MCP and MJ. Fruit were kept at 20 °C for 17 days after treatment. Ethylene production, respiration, and color change were all inhibited following MCP treatment. Ethylene production following MJ treatment fluctuated below and above that of controls, but was representative of postclimacteric apples at all times. Rates of respiration and color change were enhanced by MJ, even when fruit were previously treated with MCP. The results indicate that MJ can enhance rate of color change and respiration in apple fruit independently of ethylene action.
Broccoli (Brassica oleracea L. var. italica Plen) was held for 12 days at 10 °C in air or in ethylene (1 μL·L–1), with or without prior exposure to MCP (1 μL·L–1) for 12 hours. In a second experiment, the effects of concentration of MCP, prior to exposure to ethylene, were evaluated. Treatment with MCP reduced whereas exposure to ethylene stimulated respiration and yellowing. Treatment with MCP before continuous exposure to ethylene negated the effects of ethylene. The inhibitory effect of MCP on respiration of broccoli exposed to 1 μL·L–1 ethylene was concentration-dependent, while the effect on yellowing was not. The results indicate that the yellowing of broccoli is mediated by ethylene action, and that MCP treatment inhibits yellowing and reduces respiration, even when broccoli is exposed to ethylene. Chemical name used: 1-methylcyclopropene (MCP).
Developments in analytical technology, most notably high resolution fused silica open tubular (FSOT) gas chromatography-mass spectromety (GC-MS), make it possible to investigate physiological roles of volatile molecules occurring at low (ppb-ppm) concentrations. Use of headspace and purge-and-trap sampling coupled with cryofocusing injection techniques minimizes artifacts often created when more traditional methods of volatile molecule extraction are used. A challenging aspect of the work is development of appropriate delivery methods for internal standard quantitation of the molecules of interest. Apparently, biosynthesis of certain volatile substances is O2 dependent and others are manufactured in response to a changing environment. FSOT GC-MS investigation revealed dramatic changes in content and quantity of `Bisbee' apple headspace and purgable flesh volatiles during a 5-week harvest maturity period and 4 months of subsequent refrigerated storage. Other studies with apple mesocarp cultures and other fruits show interesting volatile molecule profiles in response to different treatments.
`Bing' and `Rainier' sweet cherry (Prunus avium L.) fruit treated with 1-methylcyclopropene (1-MCP) were stored at 20 °C in air or 35 μL·L-1 ethylene. Ethylene production by both `Bing' and `Rainier' fruit stored in air was transiently stimulated following 1-MCP treatments, however, there were no significant effects of 1-MCP on respiration rate. Exogenous ethylene stimulated respiration regardless of prior treatment with 1-MCP. Although 1-MCP treatment reduced the increase in `Bing' respiration induced by ethylene, the reduction was less than reported previously for climacteric fruit. These results suggest that stimulation of sweet cherry fruit respiration by ethylene occurs via a process that may be independent of receptors to which 1-MCP binds. Postharvest changes in fruit color and development of stem browning were not altered by 1-MCP treatment, and exogenous ethylene accelerated the development of stem browning regardless of prior treatment with 1-MCP.