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  • Author or Editor: Harold E. Nordby x
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In previous studies squalene was shown to be synthesized in grapefruit under temperature-conditioning parameters optimal for preventing chilling injury (CI). In this study, squalene and its saturated derivative squalane were applied to the fruit as sprays or dips under various protocols. Fruit were stored for various times under conditions conducive to CI. The best results were obtained when fruit were sprayed with squalene dissolved in hexane. After 4 weeks at 5C, 5% squalene reduced CI 69% and 10% squalene reduced CI 80% whereas, temperature conditioning reduced CI by a comparable amount (67%).

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The purpose of this study was to identify compounds in the wax of fruit obtained from different canopy positions for possible relationships to chilling injury development. Both exterior and interior canopy grapefruit wax extracts were separated by thin layer chromatography into four lipid classes: alkanes, aldehydes, linear alcohols and triterpenes. The triterpene class consisted of three subclasses: triterpenols (TOH), triterpenones (TON) and triterpenol acetates (TAC). Each triterpene subclass was analyzed by gas chromatography and their component structures estimated by comparison of retention times with authentic standards. Derivatives were prepared for each subclass: TOH were oxidized to TON, TON were reduced to TOH, and TAC hydrolyzed to TOH. Structures were verified by gas chromatography-mass spectra of components and their derivatives as well as spectra of authentic standards and their derivatives. There was a higher level of TON in interior compared with external canopy fruit. The three major TON were a amyrone, β amyrone and friedelin. α amyrone was also shown to be a major component of the wax of `Valencia' orange, a fruit not subject to chilling injury when produced in Florida

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It has been reported that temperature conditioning (TC), intermittent warming (IW), and film wrapping (FW) reduce chilling injury (CI) on grapefruit. Our objective was to determine if IW, FW, and vapor heat (VH) affected the composition of the epicuticular wax of grapefruit similar to the effects we previously reported with TC. Waxes were analyzed by gas chromatography. C25 to C34 aldehydes and alkanes decreased in all treatments in 5C storage for 21 days. Squalene increased in both the TC (7 days at 21C) and VH (43.5C for 4 hr) treatments. Terpenoids increased in both the TC and IW (4 cycles of 5 days at 5C and 2 days at 21C) treatments, and the greatest increase in C24 aldehyde occurred in the TC treatment. A VH-TC sequential treatment kept C27 to C34 aldehydes at fresh fruit levels following 5C storage. FW did not cause any wax increase. It is possible that these wax changes may have a role in reducing CI.

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Abstract

Saturated and mono-unsaturated hydrocarbons (C20—C35) were examined in juice sacs of ‘Clementine’ mandarin (Citrus reticulata Blanco), ‘Orlando’ and ‘Minneola’ tangelos (C. paradisi Macf. × C. reticulata Blanco), and ‘Osceola’, ‘Lee’, ‘Robinson’, ‘Nova’ and ‘Page’ hybrids [C. reticulata × (C. paradisi × C. reticulata)]. ‘Clementine’ had saturated and monoene profiles similar to those previously reported for mandarins. In the 5 mandarin × tangelo hybrids, linear hydrocarbons accounted for ca. 47% of the saturates and more than 70% of the monoenes. The major saturated hydrocarbons were C23 and C25. Except for ‘Nova’ all hybrids showed a greater total percentage of C25 over C23. The C23/C25 ratio of ‘Nova’ (1.53) was more like that of its tangelo than its mandarin parentage. Prominent amounts of C25, C27, C29 and C31 were present in the monoene fraction. All 5 ‘Clementine’ × tangelo hybrids can be differentiated from each other by their linear, monoene components. Based on these profiles, ‘Osceola’ and ‘Page’ appeared to be more like their mandarin than their tangelo parent.

Open Access

`Marsh' Grapefruit (Citrus paradisi Macf.) were temperature conditioned (7 days at 15C), wiped with hexane, treated with squalene, squalane, or safflower oil (all 10% in hexane), or waxed with a commercial fruit wax (Flavorseal) to determine their effects on weight loss, chilling injury (Cl) symptoms on the peel, and gas exchange. Following 3 weeks of storage at SC, wiping fruit with hexane resulted in a significant decrease in weight loss, but not CI. Temperature conditioning and Flavorseal independently inhibited weight loss and Cl development. Squalene inhibited CI development, but not weight loss. Chilling injury on fruit treated with squalene or Flavorseal was similar in appearance, but significantly less common than that on nontreated fruit. Grapefruit peel accounted for 92% of the gas diffusion of fruit, and resistance coefficients for peel and whole fruit were similar. Less ethane diffused into fruit that were: temperature-conditioned compared with nonconditioned, hexane wiped compared with nonhexane-wiped, and squalene-treated compared with nonsqualene treated fruit. Ethane influx was significantly restricted into squalane- and squalane-treated fruit compared with Flavorseal- or safflower oil-treated fruit. Oxygen and CO2 influx was significantly reduced by Flavorseal, safflower oil, squalene, and squalane. Squalane was the most restrictive of ethylene efflux followed by safflower oil, squalene, and Flavorseal. All of these surface treatments are known to reduce CI on grapefruit. These data indicate that water loss is less important to the development of Cl than has been previously suggested, and that the beneficial effects of squalene are not the result of an inhibition of water loss. Permeability of grapefruit peel to gases other than H2O vapor may also influence the expression of Cl.

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Differences in chilling injury (CI) susceptibility between `Marsh' grapefruit (Citrus paradisi Macf.) from interior and exterior tree canopy positions were analyzed to investigate the hypothesis that epicuticular wax morphology and composition influence CI development during low-temperature storage. The sun-exposed surface of fruit from the exterior canopy had significantly more CI and larger wax platelets than the shaded surface of the same fruit. Interior canopy fruit had significantly less CI and smaller wax platelets than exterior canopy fruit. Hydrocarbons, primarily n-alkanes, were significantly more abundant in the epicuticular wax on the surfaces of sun-exposed and exterior fruit compared with surfaces of shaded and interior fruit, respectively. Results of this study suggest that epicuticular wax plays a role in the development of external CI symptoms on grapefruit.

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The effects of temperature conditioning (7 days at 21C), application of safflower oil, squalane or squalene (all 10% in hexane spray), and a commercial wax (Flavorseal) on gas diffusion of `Marsh' grapefruit (Citrus paradisi Macf.) were studied. Gas diffusion was determined by either ethane influx or ethylene efflux. Less ethane diffused into fruit that were temperature conditioned compared with nonconditioned, and into squalene-treated compared with nonsqualene-treated fruit. As a percent of non-treated controls, ethane influx was 83, 60, 25, and 14 for the surface treatments Flavorseal, safflower oil, squalene and squalane, respectively. Surface treatments were also applied to fruit that were producing ethylene due to previous chilling injury. Squalane was the most restrictive of ethylene efflux followed by safflower oil, squalene, and Flavorseal. All of the surface treatments used have been reported to reduce chilling injury in grapefruit. Perhaps, their molecular structure influences the expression of chilling injury.

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Abstract

Major leaf alkanes (C29-C33) of 2 scions on 10 rootstocks of citrus were examined by gas chromatography. A small but definite effect of the rootstock on the alkane profiles of the scions was observed. The effect of rootstock on alkane patterns in juice sacs was very small. Rootstock affected the fatty acid patterns of total and neutral lipids as well as of triglycerides and sterol esters.

Open Access

Abstract

Long-chain alkanes present in epicuticular wax of citrus leaves changed in composition as the leaves matured. From 89 to 95% of the hydrocarbons in the mature leaves were linear, saturated, and C29 to C33 compounds. Alkane profiles changed during the year but were not influenced by the period of leaf flush (spring or fall). The alkane profiles for 67 citrus cultivars, representing 11 citrus biotypes, were determined by gas liquid chromatography (GLC). The mean alkane profile of 9 of the bio types were distinct from the others as determined by Duncan's multiple range test, Twelve other citrus and related taxa were examined, and the profile of each showed possible inheritance patterns.

Open Access