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D.R. Rudell, D.S. Mattinson, J.K. Fellman, and J.P. Mattheis

`Fuji' apple (Malus ×domestica Borkh.) fruits were harvested periodically prior to and during fruit ripening. Ethylene evolution and respiration rates of skin, hypanthial, and carpellary tissue was determined in each fruit. Additionally, whole fruits were used for analyses of internal ethylene concentration, volatile evolution, starch content, flesh firmness, and soluble solids content. Ethylene production was greatest in the carpellary tissue at all sampling dates except the one occurring just before the rise in whole fruit internal ethylene concentration, when production in the skin and carpellary tissue was similar. Respiration was always highest in the skin, in which the climacteric rise was most drastic. Higher ethylene production in the carpellary tissue of pre- and postclimacteric fruit and higher respiration in the skin tissue, including a noticeable climacteric rise, is indicative of a ripening initiation signal originating and/or transduced through the carpels to the rest of the fruit.

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Xuetong Fan, J.P. Mattheis, M.E. Patterson, and J.K. Fellman

Several strains of Fuji apples were harvested weekly from September through October in 1990 and 1991, and evaluated for maturation and quality after 1 and 7 days at 20 °C following harvest and storage in atmospheres of 0.5%, 1.0%, 2.0% O2 and air. Results showed that Fuji apples have very low ethylene production rates and little firmness loss during maturation. A change in the postharvest respiration pattern preceded the increase ethylene synthesis. Oxygen concentration during storage directly affected apple respiration rate after removal from storage. Ethylene production rates and internal ethylene concentrations indicated that the apples were still in the preclimacteric stage after 7 to 9 months storage at 0.5%, 1.0%, or 2% O2. Fuji apples develop watercore and tend to have a particular type of corebrowing during maturation on the tree, or during and after storage. The cause is unknown.

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Ahmed El Ghaouth, Rathy Ponnampalam, and Joseph Arul

The effect of chitosan coating on the respiration rate, ethylene production and quality attributes of tomatoes stored at 20°C under high humidity-regular atmosphere was investigated. Chitosan coating reduced significantly the respiration rate and ethylene production of tomatoes, with a greater effect at higher concentration. In addition coating modified the internal microatmoaphere of fruits. Furthermore, coated fruits were firmer, higher in titratable acidity, less decayed and their change in color proceeded at a slower rate than the control.

In conclusion chitosan coating delayed senescence and prolonged storage life of tomatoes, without affecting their market quality by acting as diffusion barrier for gases.

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Zhiguo Ju and Eric A. Curry

At harvest, internal ethylene was >0.5 mL·L–1 and α-farnesene concentrations were below detectable levels in `Golden Supreme', `Delicious', and `Granny Smith' apples. After 30 days of storage at 20 °C, control fruit produced high levels of internal ethylene and α-farnesene. Lovastatin at 100 to 1000 mL·L–1 did not affect ethylene synthesis, but significantly inhibited α-farnesene production. In `Golden Delicious', ethephon treatment increased ethylene synthesis in lovastatin-treated fruit but did not stimulate α-farnesene production. In lovastatin-treated fruit peel of `Delicious' and `Granny Smith', mevalonate (MAL) and farnesyl pyrophosphate (FPP) induced α-farnesene production, but hydroxymethylglutaric acid (HMG) did not. The induction of α-farnesene synthesis by MAL and FPP was concentration-dependent. Precursor feeding did not affect ethylene production in fruit peel. When high level of α-farnesene was detected in fruit peel (5 mm thick), it was not found in outer (adjacent to peel) and inner cortex (mid of flesh) tissues. Adding HMG, MAL, and FPP induced α-farnesene biosynthesis in both cortex tissues. When lovastatin was added to the feeding solution, MAL and FPP induced α-farnesene production but HMG did not.

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Peter D. Petracek, D. Frank Kelsey, and Craig Davis

The effect of high-pressure washing (HPW) on the surface morphology and physiology of citrus fruit was examined. Mature white (Citrus paradisi Macf. `Marsh') and red (Citrus paradisi Macf. `Ruby Red') grapefruit, oranges (Citrus sinensis L. `Hamlin'), and tangelos (Citrus reticulata Blanco × Citrus paradisi Macf. `Orlando') were washed on a roller brush bed and under a water spraying system for which water pressure was varied. Washing white grapefruit and oranges for 10 seconds under conventional low water pressure (345 kPa at cone nozzle) had little effect on peel wax fine structure. Washing fruit for 10 seconds under high water pressure (1380 or 2760 kPa at veejet nozzle) removed most epicuticular wax platelets from the surface as well as other surface debris such as sand grains. Despite the removal of epicuticular wax, HPW did not affect whole fruit mass loss or exchange of water, O2, or CO2 at the midsection of the fruit. Analysis of the effect of nozzle pressure (345, 1380, or 2760 kPa), period of exposure (10 or 60 seconds), and wax application on internal gas concentrations 18 hours after washing showed that increasing nozzle pressure increased internal CO2 concentrations while waxing increased internal ethylene and CO2 concentrations and decreased O2 concentrations. An apparent wound ethylene response was often elicited from fruit washed under high pressures (≥2070 kPa) or for long exposure times (≥30 seconds).

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Robert A. Saftner, William S. Conway, and Carl E. Sams

Effects of postharvest pressure infiltration of distilled water, CaCl2 solutions at 0.14 or 0.27 mol·L-1 without and with subsequent fruit coating treatments of preclimacteric `Golden Delicious' [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. `Golden Delicious'] apples on volatile levels, respiration, ethylene production, and internal atmospheres after storage at 0 °C for 1 to 6 months, and during subsequent shelf life at 20 °C were investigated. Over 30 volatiles were detected, most of the identified volatiles were esters; the rest were alcohols, aldehydes, ethers, a ketone, and a sesquiterpene. Pressure infiltration of water and increasing concentrations of CaCl2 resulted progressively in reduced total volatile levels, respiration, ethylene production, and internal O2 levels and increased CO2 levels in fruit following 2 to 4 months storage in air at 0 °C. Total volatile levels, respiration, ethylene production, and internal atmospheres of CaCl2-treated apples at 0.14 mol·L-1 gradually recovered to nontreated control levels following 2 weeks of shelf life at 20 °C and/or storage at 0 °C in air for more than 4 months. Following the calcium treatments with a shellac- or wax-based coating had similar but stronger and more persistent effects on volatile levels, respiration, ethylene production, and internal atmospheres than those found in fruit treated with CaCl2 alone. Calcium infiltration did not change the composition of volatile compounds found in fruit. Results suggest that pressure infiltration of `Golden Delicious' apples with CaCl2 solutions transiently inhibited volatile levels, respiration, and ethylene production, in part, by forming a more-or-less transient barrier to CO2 and O2 exchange between the fruit tissue and the surrounding atmosphere.

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C.B. Watkins and J.F. Nock

The inhibitor of ethylene binding, 1-methylcyclopropene (1-MCP) has been applied to `Gala', `Cortland', `McIntosh', `Empire', `Delicious', `Jonagold', and `Law Rome' apples under air and/or controlled atmosphere (CA) storage conditions. 1-MCP gas concentrations ranged from 0 to 2 mL·L–1. Effects of 1-MCP were greater in CA than air storage. A dose response of internal ethylene concentrations and flesh firmness to 1-MCP was found in cultivars such as `McIntosh' and `Law Rome', whereas in others, such as `Delicious' and `Empire', ripening was generally prevented by all 1-MCP concentrations. We have further investigated the effects of 1-MCP on `McIntosh' by increasing rates of the chemical to 50 mL·L–1, and confirming that fruit of this cultivar respond poorly if fruit have entered the climacteric prior to 1-MCP application. Efficacy of 1-MCP is affected by cultivar and storage conditions, and that successful commercial utilization of the chemical will require understanding of these relationships.

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J.P. Mattheis, D.A. Buchanan, and J.K. Fellman

Quantitative and qualitative changes in net production of volatile compounds by apples occurs during fruit development with a major transition to ester production occurring as fruit ripening begins. Ester production during fruit ripening is an ethylene-mediated response; however, differences in maturation patterns among apple cultivars led us to examine the relationship between ester production and onset of the ethylene climacteric in several commercial apple cultivars. Emission of volatile esters as a function of apple fruit development was evaluated for `Royal Gala', `Bisbee Delicious', `Granny Smith', and `Fuji' apple fruit during two harvest seasons. Apples were harvested weekly and analyses of harvest maturity were performed the day after harvest. Non-ethylene volatiles were collected from intact fruit using dynamic headspace sampling onto Tenax traps. Fruit from each harvest was stored at 1°C in air for 5 months (3 months for `Royal Gala') plus 7 days ripening at 20°C, then apples were evaluated for the development of disorders. The transition to ester production occurred after internal ethylene exceeded 0.1 μL for `Royal Gala', `Bisbee Delicious', and `Fuji'. Ester emission by `Granny Smith' apples remained low throughout the harvest period. Increased ester emission occurred after the optimum harvest date (as determined by the starch index and internal ethylene concentration) for controlled-atmosphere storage of `Bisbee Delicious' and prior to optimum maturity for `Royal Gala' and `Fuji'. A relationship between the potential for development of superficial scald and ester production at harvest was evident only for `Bisbee Delicious' apples.

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Jacqueline K. Burns, Ulrich Hartmond, and Walter J. Kender

The abscission action of two sulfonylureas and one imidazolinone was evaluated in laboratory studies with harvested orange (Citrus sinensis L. cv. Valencia) fruit and greenhouse studies with orange (cv. Hamlin) and grapefruit (Citrus paradisi Macf. cv. Marsh) trees. Dipping harvested fruit in 90 mg·L–1 imazameth, 2 mg·L–1 metsulfuronmethyl, or 30 mg·L–1 prosulfuron solutions increased levels of internal ethylene. Internal ethylene concentration was higher when fruit were dipped in 2 mg·L–1 metsulfuron-methyl solutions at low pH. Fruit retained on trees and dipped in 2 mg·L–1 metsulfuron-methyl solutions produced more ethylene than control fruit. Drop of treated fruit began when ethylene production was at a maximum. High temperatures (average 33 °C) suppressed ethylene production and fruit drop of metsulfuron-methyl–treated fruit. The results indicate the importance of environmental conditions in evaluating the potential of sulfonylureas and imidazolinones as abscission agents for citrus. Chemical names used: ±-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid (imazameth); methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2yl) amino] carbonyl] amino] sulfonyl] benzoate (metsulfuron-methyl); 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl) phenylsulfonyl] urea (prosulfuron); N-(phosphonomethyl) glycine (glyphosate); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H-imidazol-2-yl]-3-quinolinecarboxylic acid (imazaquin).

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Zhiguo Ju and Eric A. Curry

Lovastatin is a specific hydroxymethylglutaryl coenzyme-A reductase inhibitor in animals and as such, is a potent cholesterol lowering pharmaceutical for human use. Because it has also been shown to inhibit α-farnesene in certain plants, we investigated its effects on ethylene and α-farnesene biosynthesis, volatile production, and fruit color during ripening in `Golden Supreme' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. Immediately after harvest, fruit were dipped in Lovastatin solution for 2 min, allowed to dry, and stored in the dark at 20 °C for 30 days. Internal ethylene at harvest was low (< 0.1 mL·L-1) and α-farnesene was undetectable. Both internal ethylene and α-farnesene increased in nontreated fruit during 30 days storage. Prestorage Lovastatin treatment did not affect ethylene synthesis, but at 1.25 or 2.5 mmol·L-1 nearly eliminated α-farnesene production. At 0.25 mmol·L-1, Lovastatin delayed the increase in α-farnesene production about 12 days and reduced total α-farnesene production by the end of storage compared with controls. When applied to nontreated preclimacteric fruit, ethephon at 1.4 mmol·L-1 increased both internal ethylene concentration and α-farnesene production. In Lovastatin-treated preclimacteric fruit, however, ethephon increased internal ethylene concentration without promoting α-farnesene synthesis. In another trial, after 30 days storage at 0 °C, fruit were treated with 1.25 mmol·L-1 Lovastatin and stored at 20 °C with air circulation for 20 days. These fruit accumulated similar amounts of ethylene as nontreated controls, but α-farnesene production decreased rapidly and was not detectable after 5 days. Treating with ethephon at 1.4 mmol·L-1 increased α-farnesene production in control fruit but not in Lovastatin-treated fruit. Lovastatin treatment did not affect the change in fruit color. Chemical names used: [1S-[1α (R °), 3α, 7β, 8β (2S °, 4S °), 8ab]]-1,2,3,7,8,8α-hexahydro-3,7-dimethyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1-naphthaienyl 2-methylbutanoate (Lovastatin); 2-chloroethylphosphonic acid (ethephon).