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- Author or Editor: Roy E. McDonald x
Abstract
Chilling injury (CI) of lemons (Citrus limon Burm. f.) was reduced by temperature-conditioning at 10, 15, 21, or 27C immediately before storage at 1C. CI was less severe in lemons temperature-conditioned for 7 vs. 3 days. However, the process is not recommended for avoiding CI in lemons stored at low temperatures because of the wide range in treatment effects. Following conditioning at 21 and 27C, putrescine concentrations increased in flavedo tissue and were also higher in fruit after storage at 1C than at 10C, regardless of conditioning temperature. After holding fruit for 2 weeks at 21C, putrescine levels were higher in lemons that had been stored at 10C than in those stored at 1C. Prestorage temperature-conditioning did not affect spermidine levels, which tended to be higher in fruit stored at 10C than at 1C after storage and subsequent holding at 21C.
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%).
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
Preharvest gibberellic acid (GA) applications at 10 ppm in 0.1% L-77 (v/v) surfactant or 20 ppm in 0.05% L-77 (v/v) caused `Marsh' grapefruit (Citrus paradisi Macf.) to be significantly more resistant to puncture and significantly delayed yellow color development. There was no difference between the two GA rates and applications in July were not found to be as effective as August or September applications. There was an overall significant increase in peel oil content in flavedo tissue as a result of GA treatment, but no significant difference between GA treatments. Limonin contents in GA-treated grapefruit albedo tissue were generally higher at both GA levels than in control fruit. GA treatments had no effect on juice quality characteristics and there was no difference in taste preference between GA-treated and control fruit. Because citrus fruit are resistant to attack by tephritid fruit flies prior to the occurrence of peel senescence and GA delays peel senescence, GA treatment should provide a biorational addition to existing fruit fly control strategies.
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.
Mature green mango (Mangifera indica L.) fruit were heated (100% RH) at 50C for 120, 180 or 240 min or 46C for 160, 220 or 280 min. The rate of mesocarp color (CIE a*) development was reduced in treated fruit, particularly in inner tissue. Rate of softening of mesocarp tissue was reduced after heat treatment; inner more than outer. Fruit treated at 50C remained more firm than control fruit 9 days after treatment, whereas fruit treated at 46C were more firm than controls 3 days after treatment, but were similar by 9 days. Electrolyte leakage from inner mesocarp tissue disks increased with increasing time at 50C, but was unchanged in fruit treated at 46C. However, after 3 days, electrolyte leakage returned to control levels. Ethylene-forming enzyme (EFE) activity of inner meso-carp tissue was greatly reduced in fruit treated at 50C (all times), and at 46C (220 and 280 min). After 3 days, EFE activity of fruit from most treatments had recovered to levels higher than controls. These data indicate that fruit may be able to recover from heat stress. Mild heat stress may increase postharvest shelf life by reducing the rate of softening.
`Marsh' white grapefruit (Citrus paradisi Macf.) harvested from exterior canopy positions were less tolerant of 0.5 or 1.0 kGy irradiation than were interior fruit. Irradiation at 0.0, 0.5, or 1.0 kGy resulted in 0.0%, 24.3%, and 37.5% surface pitting of fruit, respectively. Pitting was reduced 30% by temperature conditioning with vapor heat at 38 or 42 °C for 2 hours. Exterior canopy fruit had ≈2-fold more pitting, had greater weight loss, and were firmer than interior canopy fruit. Fruit weight loss increased and firmness decreased as conditioning temperature and irradiation dose increased. Total soluble solids, titratable acidity, and flavor decreased with increasing irradiation dose. The peel of exterior canopy grapefruit was damaged more by irradiation than was that of interior fruit, but irradiation damage was reduced by temperature conditioning.
`Keitt' and `Tommy Atkins' mango (Mangifera indica L.) fruit were evaluated for selected ripening criteria at six ripening stages, from mature green to overripe. `Tommy Atkins' mangos developed more red and yellow pigmentation (CIE a* and b*) in peel and mesocarp tissues than `Keitt'. The outer mesocarp of `Keitt' remained firm longer than `Tommy Atkins', and the inner mesocarp was softer than the outer at each stage in both cultivars. Cell wall neutral sugars, particularly arabinosyl, rhamnosyl, and galactosyl residues, decreased with ripening in both cultivars. `Keitt' had more loosely associated, chelator-soluble pectin, accumulated more soluble polyuronides, and retained more total pectin at the ripe stage than `Tommy Atkins'. Both cultivars had similar polygalacturonase (EC 3.2.1.15) activity which increased with ripening. The amount and molecular weight of cell wall hemicellulose decreased with ripening in both cultivars. These data indicate that enzymatic and/or nonenzymatic processes, in addition to polygalacturonase activity, are involved in the extensive softening of mango fruit.
Abstract
Rootstocks affected decay of grapefruit (Citrus paradisi Macf. cv. Redbush) stored for 9 weeks at 10°C plus 1 week at 21°. Fruit from trees on ‘Smooth Seville’ (Australian sour orange) was least susceptible to decay, 3.3%. Fruit from trees on the hybrid C61-253 (‘Shekwasha’ × ‘Chinotto’) was the most susceptible, 27.7%. Postharvest decay was statistically related to rootstocks but not to standard fruit quality characteristics.