Search Results
You are looking at 31 - 40 of 40 items for
- Author or Editor: R. E. McDonald x
Freshly harvested mangos (Mangifera indica L.) treated with forced air at 51.5C for 125 minutes then stored for 1, 2, or 3 weeks at 12C, followed by 21C until soft-ripe, were compared with nontreated fruit for quality changes. Treated fruit lost 1.0% more fresh weight than nontreated fruit and deveoped trace amounts of peel pitting. Total soluble solids concentrations for treated and nontreated fruit were similar (≈q3%), as was peel color at the soft-ripe stage. Treated fruit generally reached the soft-ripe stage ≈q day earlier than nontreated fruit regardless of storage duration and had a lower incidence and severity of stem-end rot and anthracnose. The trace of pitting on treated fruit likely will not influence consumer acceptance.
Irradiation is being evaluated as a quarantine treatment of grapefruit (Citrus paradisi Macf. `Marsh'), but it can cause damage to the fruit. Research was conducted to determine if preirradiation heat treatments would improve fruit tolerance to irradiation as they improve tolerance to low temperature injury and to determine if canopy position influenced fruit tolerance to irradiation. Initially, grapefruit were irradiated at 0 or 2.0 kGy at a dose rate of 0.14 kGy·min-1 and selected biochemical changes were monitored over time. There was a marked increase in phenylalanine ammonia-lyase (PAL) activity following irradiation. Maximum activity (≈18-fold increase) was attained 24 hours after irradiation. Subsequently, grapefruit were harvested from interior and exterior canopy positions and irradiated at 0 or 1.0 kGy at a dose rate of 0.15 kGy·min-1 before storage for 4 weeks at 10 °C. Following storage, pitting of flavedo was the most evident condition defect noted as a result of irradiation. Pitting was observed on 27% and 15% of irradiated exterior and interior canopy fruit, respectively, whereas there was no pitting on nonirradiated fruit. Heat treatment before irradiation decreased susceptibility of fruit to damage. Pitting was 26%, 19%, and 17% when fruit were held 2 hours at 20 (ambient), 38 or 42 °C, respectively. Irradiation-induced PAL activity was reduced by temperature conditioning at 38 or 42 °C. Exterior canopy fruit flavedo contained higher levels of total phenols, including flavanols and coumarins compared with interior canopy fruit. Deposition of lignin was not related to canopy position. Neither irradiation nor heat treatment had an effect on total phenols or lignin deposition. Generally, cholesterol, campesterol, stigmasterol, β-sitosterol, and isofucosterol were found to be higher in four steryl lipid fractions in exterior canopy fruit compared with interior canopy fruit. Irradiation increased campesterol in the free sterol and steryl glycoside fractions and decreased isofucosterol in the free sterol fraction. Heat treatments had no effect on individual sterol levels. It seems that irradiation causes a stress condition in the fruit, which leads to pitting of peel tissue. Heat treatment before irradiation reduced damaging effects of irradiation.
Postharvest quality of `Climax' rabbiteye blueberries (Vaccinium ashei Read) was evaluated after exposure to dosages of 0, 0.75, 1.5, 2.25, or 3.0 kGy gamma irradiation (0.118 kGy·min-1) and after subsequent storage. Irradiation did not affect weight loss, but irradiated berries were softer than nontreated berries. There was also a trend toward increased decay as dose increased. Irradiation had no effect on powdery bloom or surface color; total soluble solids concentration, acidity, and pH were affected slightly. Flavor preference was highest for nonirradiated berries and generally declined as dosage increased. Irradiation at 2.25 and 3.0 kGy resulted in increased levels of xylosyl residues in cell walls, and xylosyl residues were the most abundant cell-wall neutral sugar detected in blueberries. There was no evidence of cell wall pectin loss in irradiated berries. Irradiation at 21.5 kGy lowered the quality of fresh-market `Climax' blueberries.
The fungicides thiabendazole (TBZ) or imazalil were applied at 1 g·liter-1 at 24 or 53C to `Marsh' and `Redblush' grapefruit (Citrus paradis i Macf.) to reduce fruit susceptibility to chilling injury (CI) and decay. There was more CI and decay on `Marsh' grapefruit than on `Redblush'. CI was found to be lower in grapefruit that had been dipped at 53C than at 24C. CI was higher after water dips without fungicide. Imazalil was found to be more effective in reducing CI than TBZ. Fungicides reduced decay at both temperatures, and imazalil was better than TBZ. Results of this study confirm the benefits of high-temperature fungicide treatments for maintaining grapefruit quality and indicate some benefits of high-temperature fungicide treatments for reducing CI.
Chopped `Salinas' crisphead lettuce (Lactuca sativa L.) was packaged in four types of polymeric films and stored at 1 or 5C for 14 days. Discoloration and off-flavors developed in lettuce stored in the two films in which the naturally produced CO2 rose above 20%. In the two films (oriented low-density polyethylene) with O2 transmission rates higher than 3000 ml·m-2· day-1·atm-1 at 22C, CO2 remained below 20%, O2 was between ≈ 2% and 15%, and the lettuce was acceptable after 14 days of storage at either 1 or 5C. Appearance and flavor were affected more by temperature than by length of storage.
Abstract
Strains of Penicillium digitatum (Sacc.) and P. italicum (Wehmer) resistant to thiabendazole and benomyl were isolated from decaying citrus fruits obtained from the Rotterdam, Netherlands, terminal market and originating from 18 countries. Significantly more Penicillium sp isolates with resistance to thiabendazole and benomyl were collected from grapefruit and lemons than from oranges. Significantly more isolates of P. digitatum than P. italicum grew on agar plates with 4, 10, or 40 ppm thiabendazole. A greater percentage of P. digitatum than P. italicum isolates grew on 4 and 10 ppm benomyl-agar plates, but a greater percentage of P. italicum than P. digitatum isolates grew on 40 and 80 ppm benomyl-agar plates. Both species were more resistant to thiabendazole than to benomyl, and often showed cross-resistance to the fungicides. Resistant Penicillium sp isolates produced larger colonies on 4 and 10 ppm thiabendazole and 40 and 80 ppm benomyl.
Abstract
Film-wrapped cucumbers (Cucumis sativus L.) stored 14 or 21 days at 7°C plus 3 days at 21° had less weight loss than nonwrapped cucumbers but not less than waxed or wrapped/waxed cucumbers. Waxed cucumbers, however, had an increased incidence of decay 3 days after transfer to 21°, from a 14- and 21-day storage period at 7°. Wrapped cucumbers had a higher incidence of decay than nonwrapped cucumbers only after 21 days of storage at 7°. Dipping of cucumbers in imazalil (IM) reduced the incidence of decay during all storage periods. While wrapping cucumbers did not increase volatile production, waxing increased emanations of acetaldehyde, ethanol, and methanol, indicating anaerobic respiration. Chemical names used: l-[2-(2,4-dichlorophenyl)-2-(2-propenyloxy)ethyl]-1H-imidazole (imazalil).
Abstract
Rabbiteye blueberries, Vaccinium ashei (Reade), were stored in each of 3 containers and 4 time-temperature regimes: 24 hr at 1°C + 24 hr at 10° + 24 hr at 21°; 48 hr at 10° + 24 hr at 21°; 7 days at 1°; and 14 days at 1°. Berries of ‘Tifblue’ lost less weight, were firmer, had fewer “leakers” and less decay than those of ‘Woodard’ following storage under identical treatments and storage conditions. When means of both cultivars and 4 time-temperature treatments were combined, there was an effect of consumer packaging type on weight loss, but there was no effect on berry firmness or the incidence of “leakers” and decay. There was no effect of packaging type on the percentage of sugars during 1 and 2 weeks of storage at 1°.
Experimental vapor heat (VH) tests [43.5C for 5 hours, 1009” relative humidity (RH)] were conducted to determine treatment effects to freshly harvested Florida grapefruit (Citrus paradisi Macf.). VH treatment reduced peel pitting 5-fold compared to control fruit after 5 weeks of storage (4 weeks at 10C + 1 week at 21C) and did not cause peel discoloration or rind breakdown. There was no difference in volume between treated and nontreated fruit after 1 week of storage or in weight loss after 5 weeks. Also, peel color, total soluble solids concentration, acidity, and pH were not affected by VH treatment. Fruit were slightly less firm after VH treatment and remained less firm throughout storage, compared with control fruit. The VH treatment tested is a potentially viable alternative quarantine treatment for control of the Caribbean fruit fly [Anastrepha suspensa (Loew)] because it is not phytotoxic to grapefruit and has been reported effective for disinfestation of this pest in grapefruit.
The fungicides thiabendazole (TBZ) or imazalil were applied at 1 g·liter-1 at 24 or 53C to `Marsh' and `Redblush' grapefruit (Citrus paradisi Macf.) to reduce fruit susceptibility to chilling injury (CI) and decay. Generally, there was more CI and decay on `Marsh' grapefruit than on `Redblush'. Severity of CI was lower in grapefruit that had been dipped at 53C than at 24C. Fruit dipped in fungicides had less CI than fruit dipped in water alone. Imazalil was more effective in reducing CI than TBZ. Fungicides reduced decay at both temperatures, and imazalil was better than TBZ. Chemical names used: 2-(4-thiazolyl)benzimidazole (thiabendazole, TBZ); 1-[2-(2,4-dichlorophenyl)-2-(2-propenyloxy)ethyl] -1H -imidazole (imazalil).