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H.P.V. Rupasinghe, G. Paliyath and D.P. Murr

α-Farnesene is an acyclic sesquiterpene hydrocarbon that is a constituent of the volatile components and the surface wax of apples (Malus ×domestica Borkh.). Although oxidation products of α-farnesene have been implicated in the development of superficial scald in apples, the relation between α-farnesene biosynthesis and scald development is not well understood. In vivo labeling studies using isolated tissue segments showed that α-farnesene is derived from trans,trans-[1,2-14Cor 1-3H]-farnesyl pyrophosphate (FPP) mostly in the skin rather than cortex tissue. Among other labeled products, farnesol was >100-fold higher compared to α-farnesene. However, HPLC analysis of hexane-extractable components from apple skin revealed farnesol is not a predominant natural constituent of apple skin tissue. In addition, trans,trans-[1-3H]-farnesol was not converted to α-farnesene by apple skin tissue. Our results indicate that biosynthesis of α-farnesene in apple tissue occurs through the isoprenoid pathway, and the conversion of FPP to α-farnesene is catalyzed by a single sesquiterpene synthase enzyme, trans,trans-α-farnesene synthase, rather than via farnesol as an intermediate. A comparison of α-farnesene biosynthesis between scald-developing and scald-free regions of the same apple showed that incorporation of radiolabel into α-farnesene from trans,trans-[1-3H]-FPP was nearly 3-fold lower in scald-developing skin tissue than in scald-free skin tissue.

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Charles F. Forney

Volatile compounds are responsible for the aroma and contribute to the flavor of fresh strawberries (Fragari×anannassa), red raspberries (Rubus idaeus), and blueberries (Vaccinium sp.). Strawberry aroma is composed predominately of esters, although alcohols, ketones, and aldehydes are also present in smaller quantities. The aroma of raspberries is composed of a mixture of ketones and terpenes. In highbush blueberry (Vaccinium corymbosum), aroma is dominated by aromatic hydrocarbons, esters, terpenes and long chain alcohols, while in lowbush blueberries (Vaccinium angustifolium), aroma is predominated by esters and alcohols. The composition and concentration of these aroma compounds are affected by cultivar, fruit maturity, and storage conditions. Volatile composition varies significantly both quantitatively and qualitatively among different cultivars of small fruit. As fruit ripen, the concentration of aroma volatiles rapidly increases closely following pigment formation. In storage, volatile concentrations continue to increase but composition depends on temperature and atmosphere composition. Many opportunities exist to improve the aroma volatile composition and the resulting flavor of small fruit reaching the consumer.

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K.C. Cushman, T.W. Tibbitts, M. Anderson, X. Fu and W. Zeltner

The performance of a reactor designed to convert volatile hydrocarbons to carbon dioxide and water by a combination of surface chemistry and UV radiation was tested under conditions relevant to horticulture. Air containing 65 to 1100 nL·L–1 ethylene gas passed through a bed of catalyst crystals at a rate of 0.1 to 2.0 L·min–1. The catalyst bed consisted of 14 g of zirconia-titania particles, 0.50 to 0.75 mm in size, that occupied the space between a 4-W UV lamp and a stainless-steel housing. Dew-point temperatures of the air passing through the reactor ranged from 5 to 22°C and internal reactor temperatures ranged from 20 to 80°C. Increasing internal reactor temperature, ethylene concentration, or air flow resulted in increasing ethylene photocatalysis by the reactor. Increasing dewpoint temperature of the air stream resulted in decreasing ethylene photocatalysis by the reactor. Operation of the reactor over a 120-day period showed that reactor design and catalyst performance were stable and robust during continuous duty. Our results demonstrate that the reactor performed well over a wide range of conditions and may be useful for applications in horticulture. This research was, in part, NASA sponsored, and a reactor similar in design to that used in our studies has been used for plant growth in space.

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N.A. Mir and R.M. Beaudry

The changes in volatile-aroma of Penicillium expansium and Botrytis cinerea fungi and apple fruit inoculated with these fungi were studied using GC-MS. A specially designed chamber with raised end glass tubes with access ports fitted with Teflon-lined septa was used to determine the volatile profile for fungi on agar. Inoculated fruit were placed in glass flow-through chambers similarly fitted with sampling ports. Volatile collection from fruits or fungi was accomplished using solid phase micro-extraction (SPME) device (Supelco, Inc.). In fungi-inoculated fruits, volatiles not produced by uninfected fruit included formic acid, 2-cyano acetamide; 1-hydroxy-2-propanone, and 1-1-diethoxy-2-propanone, which were initially detected 6 hr after inoculation. These new volatiles are suggested to be synthesized specifically by the action of fungi on fruits as they were not detected from fungi that were grown on agar or bruised fruits. In general, esters, alcohols, aldehydes, ketones, acids, and hydrocarbons other than α-farnesene declined in fungi infected fruits.

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H.P.V. Rupasinghe, G. Paliyath and D.P. Murr

α-Farnesene is an acyclic sesquiterpene hydrocarbon that is a constituent of the surface wax of apples (Malus domestica Borkh.). Although, oxidation products of α-farnesene have been implicated in the development of the physiological disorder superficial scald in apple, the mechanism of α-farnesene biosynthesis has not been studied in detail. We are currently investigating α-farnesene biosynthesis in relation to superficial scald development in apples. Radiolabelled feeding experiments using isolated tissue segments indicated that α-farnesene is derived from trans,trans-farnesyl pyrophosphate (FPP), mainly in the skin rather than cortex. Among the other labeled products detected, farnesol level was over a hundred-fold higher compared to α-farnesene. However, [1-3H] trans,trans-Farnesol was not incorporated into α-farnesene. Feeding radiolabelled FPP to skin tissue segments of scald-developing and normal apples showed differential incorporation of radiolabel into various products. Though the incorporation into α-farnesene was nearly the same, there was higher levels of incorporation into farnesyl esters in normal apples. As well, the levels of radiolabelled in the farnesol fraction was three times higher in scald-developing regions. These results indicate that there are potential difference in the biosynthesis and metabolism of farnesyl components between scald-developing and normal apples. In studies using cell-free extracts, farnesol formation was observed from labeled FPP and was two-fold higher in crude membrane extract compared to crude cytosol. Our results indicate that α-farnesene formation in apple fruit tissue is through FPP and is possibly catalyzed by a single sesquiterpene synthase enzyme. Purification and characterization of this enzyme are in progress.

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R.S. Mueller, D.P. Murr and L.J. Skog

1-Methylcyclopropene (1-MCP), a gaseous synthetic cyclic hydrocarbon, has been shown to have potential to become an important new tool in controlling the response of plants sensitive to ethylene. Due to its irreversible binding to the ethylene receptor(s) and its subsequent prevention of the physiological action of ethylene for extended periods, 1-MCP may prove also to have effective commercial application in the control of ethylene effects in detached organs such as fruit. Our objective was to investigate the effectiveness of 1-MCP in controlling ripening in pear. Two commercial cultivars (Bosc, Anjou) and one numbered cultivar from Agriculture and Agri-Food Canada's breeding program (Harrow 607) were harvested at commercial maturity. Immediately after harvest, fruit were exposed for 24 h at 20 °C to 1-MCP ranging from 0 to 100 μL•L-1 then placed in air at 0 °C and 90% relative humidity for 5 and 10 weeks. Following treatment and after 5 weeks storage plus a 7- or 14-day post-storage ripening period, fruit softening and ethylene evolution were inhibited and fruit volatile evolution was reduced significantly by exposure to 1-MCP at or above 1.0 μL•L-1 in all three cultivars. Concentrations exceeding 1.0 μL•L-1 were required to maintain initial firmness and inhibit ethylene production after 10 weeks storage in air. Evolution of alpha-farnesene and 6-methyl-5-hepten-2-one was related to low temperature stress and chlorophyll loss as a result of ripening, respectively, and were affected by 1-MCP exposure. The pattern of evolution and amounts of other volatiles was also affected by 1-MCP treatment. These results indicate a huge potential for commercial use and application of 1-MCP in controlling fruit ripening and senescence.

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H.P.V. Rupasinghe, D.P. Murr and G. Paliyath

`McIntosh' apples were treated at 20 °C with 0.0, 0.01, 0.1, 1.0, 10, and 100 ppm 1-methylcyclopropene (1-MCP; EthylBloc™) a day after harvest for 18 h and stored at 0 °C in air. Apples were also continuously exposed to 0.0 and 25 ppm 1-MCP under controlled atmosphere (CA; 0 °C in 4.5 kPa CO2 and 3 kPa O2) by re-establishing the initial concentration at week 9 and 17. The threshold concentration of 1-MCP at 20 °C to inhibit de novo ethylene production in apple fruit was determined to be 1.0 ppm. Interestingly, the ethylene antagonist completely inhibited (99.67%) ethylene production in apples, which were removed from 0 °C in air and CA after 9 weeks and held at 20 °C up to 6 days. Overall, ethylene production was 10- to 100-fold less in apples treated with 1 ppm and above 1-MCP than in untreated apples. 1-MCP-treated apples showed less softening; fruit firmness was 2-4 Lb higher compared to untreated apples. Total soluble solids of apples was not affected by 1-MCP treatment. Total hydrophobic volatiles, including the sesquiterpene hydrocarbon α-farnesene, from apples measured by SPME/GC showed an inverse relation to 1-MCP concentration. Contents of α-farnesene and its putative superficial scald-causing catabolite, conjugated triene alcohol, in the skin were reduced 60% to 90% by 1-MCP. However, 1-MCP did not suppress the incidence of scald or other disorders, e.g., stem cavity, browning and brown core, in `McIntosh' apples.

Open access

John E. Kaminski, Tim T. Lulis and Travis R. Russell

petroleum-based oils comprised significantly of hydrocarbons. Hydrocarbons are toxic to plants and animal life, and leaks or spills can create long-term environmental hazards ( Aislabie et al., 2004 ; Bai and Li, 2013 ). In addition, these introduced

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John C. Beaulieu, Maureen A. Tully, Rebecca E. Stein-Chisholm and Javier M. Obando-Ulloa

consisted of the hydrocarbons limonene, γ-terpinene, myrcene, and α-pinene ( Yajima et al., 1979 ). Based on the 19 compounds integrated, WPJ had 61.6% limonene that increased to 80.1% on peel removal. After 7 d storage, these levels were somewhat conserved

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Ajay Nair and Brandon Carpenter

hydrocarbons (PAHs) in the biochar. Polycyclic aromatic hydrocarbons are recalcitrant, persistent, and phytotoxic compounds that can also be produced during the pyrolysis process and get adsorbed onto biochar surfaces ( Sharma and Hajaligol, 2003 ). These PAHs