Search Results

You are looking at 1 - 10 of 31 items for

  • Author or Editor: R.E. McDonald x
Clear All Modify Search
Free access

W.R. Miller and R.E. McDonald

`Marsh' and `Ruby Red' grapefruit (Citrus paradisi Macf.) tolerated a high-temperature, forced-air, vapor heat treatment of 43.5C for 260 minutes, a treatment applied for security against the Caribbean fruit fly [Anastrepha suspensa (Loew)]. Fruit did not develop symptoms of quality deterioration during subsequent storage. With `Marsh' fruit, 99% and 96% were sound, whereas with `Ruby Red' 98% and 94% were sound after storage at 10C for 28 days or 10C for 28 days plus 7 days at 21C, respectively. Differences in means for percentage of sound fruit were not significant for cultivar or vapor heat treatment. After the final storage period, there was significantly more (2.4-fold, P ≤ 0.05) aging observed on `Ruby Red' fruit than on `Marsh', averaged over all treatments. Vapor heat did not affect aging of `Ruby Red' but increased aging of `Marsh' fruit. Decay was reduced to ≈ 22.0% in vapor heat-treated fruit from 5.0% for nontreated fruit. The efficacy of thiabendazole to control stem end rot was increased on vapor heat-treated fruit compared with nontreated fruit. After the final inspection, the appearance of `Marsh' fruit was fresher (index 2.0) than that of `Ruby Red' fruit (index 2.3), but the appearance of vapor heat-treated and nontreated fruit was similar. Peel color of `Ruby Red' fruit was not affected by the vapor heat treatment, but, after 4 weeks at 10C plus 1 week at 21C, `Marsh' fruit that were not treated were greener than those treated with vapor heat. The vapor heat treatment tested is a potentially viable quarantine procedure for Florida grapefruit that can be applied without adversely affecting fruit quality during normal storage.

Free access

W.R. Miller and R.E. McDonald

`Marsh' and `Ruby Red' grapefruit (Citrus paradisi Macf.) were harvested in Florida during Oct. and Nov. 1990, degreened in an ethylene chamber, exposed to vapor heat (VH) treatment (43.5 ± 0.1C for ≈240 min), and evaluated for deterioration in quality and development of injury after various storage regimes. Symptoms of aging averaged 6% and 8% of the surface on `Ruby Red' and `Marsh' fruit, respectively, and the VH treatment had reduced the incidence of aging by 45% after 5 weeks of storage (4 weeks at 16C plus 1 week at 21C). Total decay, mostly stem-end rots (Diplodia spp. and Phomopsis spp.), remained relatively low (≈5%) in both treated and nontreated fruit after 5 weeks of storage. The VH treatment had little effect on change in peel color during treatment or subsequent storage. After the final inspection, `Marsh' fruit was higher in total soluble solids and titratable acidity than `Ruby Red' fruit, but these quality indicators and pH were not affected by the VH treatment. VH treatment did not adversely affect the quality of `Marsh' or `Ruby Red' grapefruit harvested early in the season; hence, VH should be considered as a viable quarantine treatment for Florida grapefruit.

Free access

W.R. Miller and R.E. McDonald

Low-dose irradiation (0.15 kGy) of grapefruit is reportedly a viable quarantine treatment for pests such as Caribbean fruit fly larvae, and is expected to be approved soon for use by the U.S. citrus industry. For the application of ionizing gamma irradiation to be efficacious for all fruit treated on commercial pallet units, fruit will likely require doses 3 to 4 times the required minimum dosage. Grapefruit peel is known to be slightly injured at 0.3 kGy, and can be seriously injured at 0.6 kGy but no peel injury is allowed for U.S. #1 grade fruit. A forced-air vaporheat treatment at 38°C for 2 hours reduced the severity and incidence of grapefruit peel injury by irradiation at doses to 1.0 kGy. The heat treatment reduced the incidence of peel injury at 0.5 and 1.0 kGy by about 50% and 21%, respectively. No other quality or condition attribute was affected by the combination treatment of heat and irradiation. Peel injury was not reduced however by pretreatment with thiabendazole (TBZ) at 1000 ppm or 4000 ppm, or a combination of 1000 ppm each of TBZ and imazalil. A combination treatment of heat before irradiation may allow for doses higher than attainable without heat during the application of irradiation as a quarantine treatment of grapefruit.

Free access

W.R. Miller and R.E. McDonald

`Marsh' grapefruit (Citrus paradisi Macf.) produced in Florida must be certified for security against unwanted pests before entry into some domestic and export markets. Application of heat by hot water (HW) has been shown to cause severe injury to grapefruit; however, direct comparisons between forced vapor heat (VH) and HW have been lacking. Grapefruit preharvest-treated with gibberellic acid (GA) or not treated, were postharvest-treated with VH or HW such that the surfaces of fruit were exposed to the same rate of temperature increases and treatment durations. Condition and quality attributes were then compared with ambient air (AA) and ambient water (AW) controls after storage. After 4 weeks' storage at 10 °C plus 1 week at 20 °C, scald affected 5% of HW and 20% of VH-treated fruit. No scald developed on control fruit. At the end of storage, mass loss for HW and VH fruit was ≈5%. HW-treated fruit had a 5-fold higher incidence of aging than VH fruit; however, control fruit showed significantly more aging than all heat-treated fruit. Gibberellic acid (GA) and the heat treatments reduced decay relative to the control. GA-treated fruit remained greener during storage than control fruit. These findings indicate that VH and HW treatments at the temperatures and durations to control the Caribbean fruit fly (Anastrepha suspensa, Loew) will likely cause peel injury to `Marsh' grapefruit produced in Florida, regardless of treatment with GA.

Free access

W.R. Miller and R.E. McDonald

Carambolas require quarantine treatment for security against the Caribbean fruit fly (Anastrepha suspensa Loew) (CFF) prior to shipment to certain domestic and export markets. Low-dose irradiation is effective for the control of CFF, but carambolas are susceptible to peel injury and quality deterioration at relatively low doses. Peel discoloration, stem-end breakdown, and fruit shriveling were reduced when carambolas were irradiated in polystyrene clam shell packs at 0.15 or 0.5 kGy compared with irradiation in conventional fiberboard packaging. Some pitting was observed at 5°C, but not at higher storage temperatures. Irradiation of carambolas in clam shell packaging increases the tolerance of fruit to peel and quality disorders, and improves the potential of irradiation as a quarantine treatment.

Free access

W.R. Miller and R.E. McDonald

Carambolas (Averrhoa carambola L.) require quarantine treatment for control of the Caribbean fruit fly (Anastrepha suspensa Loew) (CFF) prior to shipment to certain domestic and export markets. Low-dose irradiation, ≤1.0 kGy, is effective for sterilizing CFF and other fruit flies; however, carambolas are susceptible to irradiation-induced peel injury. Low-dose gamma irradiation treatment generally reduced fruit quality, but the effects were mitigated by packaging carambola fruit in “clamshell” polystyrene containers, rather than conventional fiberboard boxes, prior to treatment. Use of clamshell containers reduced peel pitting, stem-end breakdown, shriveling, and loss of mass after storage for 14 days at 5 or 7 °C. In addition, fruit held in clamshell containers were firmer, with slightly less green peel, and had lower total soluble solids, but the flavor was not quite as good as that of fruit stored in fiberboard boxes. There was no difference in the mastication texture or acidity of fruit by package type at final storage. Packing carambolas in clamshell containers increased their tolerance to irradiation-induced peel disorders and improved the potential for usage of low-dose irradiation for quarantine treatment.

Free access

W.R. Miller and R.E. McDonald

Carambolas (Averrhoa carambola L.) must be treated with an approved insect quarantine procedure such as cold treatment before shipment to certain markets. Condition and quality of mature-green (MG) and slightly yellow (SY) fruit were determined after they were: 1) treated with ethylene at 0.1 ml·L-1 for 48 hours (C2H4), 2) subjected to cold treatment (CT) at 1 °C for 15 days, and 3) held in storage at 5 °C for 7 days plus 3 days at 15 °C. Ethylene-treated fruit were softer and yellowness was enhanced compared with non-C2H4-treated fruit. MG fruit were firmer and lost more mass following CT and storage than SY fruit. C2H4 treatment increased the severity of peel scald, stem-end breakdown (SEB), and fin browning but had no effect on pitting. CT increased the severity of scald and pitting, and the severity of SEB, but did not affect fin browning. Peel scald, pitting, SEB, and fin browning were more severe in MG than in SY fruit at the final evaluation. C2H4-treated fruit had lower total soluble solids concentration, higher titratable acidity and pH, and a less preferred flavor and texture than control fruit. We conclude that carambola fruit should be selected at harvest at the slight-yellow stage (3% to 25% of surface area) instead of at the mature-green stage. Fruit to be cold-stored should not be C2H4 treated due to enhanced mold development and severity of SEB.

Free access

W.R. Miller and R.E. McDonald

Solo-type papaya (Carica papaya L.) fruit at the mature green (MG) or one-quarter yellow (QY) stage of maturity were imported through the Port of Miami, Fla., and either irradiated (0.675 kGy) or not irradiated. Fruit condition and quality attributes were determined after ripening to the edible ripe stage at 25 °C before and after storage for 7 days at 10, 12, or 15 °C. The incidence and severity of peel scald was increased by irradiation regardless of storage and ripening regime; however, the degree of severity was dependent on fruit maturity at irradiation. Irradiated QY fruit tended to have the most serious incidence and severity of scald. Mature green fruit ripened at 25 °C without storage had the lowest incidence of fruit with hard areas in the pulp (“lumpy” fruit). The QY fruit generally were second only to irradiated MG fruit stored at 10 °C in incidence of lumpiness. Anthracnose sp. decay and stem-end-rots affected 53% of all fruit. The least decay occurred on fruit ripened at 25 °C without storage, regardless of fruit maturity, and the most decay occurred on QY fruit with or without irradiation. Fruit ripened at 25 °C without storage had more palatable pulp (5.5 N) at the edible ripe stage than did fruit held in storage and then ripened. The effect of fruit maturity or irradiation dose on fruit firmness, however, was dependent on the storage temperature. Mature green fruit ripened at 25 °C lost less weight than did those stored at cold temperatures prior to ripening. We recommend that importers obtain fruit with only a slight break in ground color, and distribute them as rapidly as possible, while maintaining transit/storage temperatures at or above 15 °C with or without exposure to irradiation.

Free access

T.G. McCollum and R.E. McDonald

Grapefruit (Citrus paradisi) flavedo is a rich source of peroxidase (POD) (EC 1.11.1.7). Changes in POD have been related to senesence and environmental stress in a variety of plant tissues. However, due to the large number of POD isoenzymes as well as the broad substrate specificity, measurement of POD activity in crude extracts is of limited value for gaining an understanding of the role of POD in vivo. We have begun to purify and characterize POD isoenzymes from grapefruit flavedo. HPLC gel permeation chromatography reveals 2 peaks of POD activity with apparent MW of 66 kD and 30 kD. Native PAGE (8% bis-acrylamide, pH 8.8) followed by activity staining indicates that the PODs differ in Pi; the 30 kD POD migrates anodally, whereas the 66 kD POD does not migrate. Isoelectric focusing has been used to separate flavedo PODs into acid (Pi ca 4.0) and basic (Pi > 8.5) forms. Treatment of grapefruit with ethylene (2 ppm 72 hours) induces a basic POD not present in freshly-harvested fruit or in nonethylene-treated controls.