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Huating Dou

Postharvest pitting, which has severely affected citrus quality, can be caused by wax application and high temperature storage. Internal volatile composition of waxed and non-waxed fruit could be an indicator of fruit susceptibility to postharvest pitting. In this study, volatile composition was compared between pitted and non-pitted `Fallglo' tangerines [Bower citrus hybrid (citrus reticulata Blanco × C. reticulata Blanco × C. paradisi Macf.) × Temple (C. reticulata Blanco × C. sinensis L.)], as well as in white `Marsh' grapefruit (C. paradisi Macf.). Pitted fruit had a higher volatile concentration than non-pitted `Fallglo' tangerines or white `Marsh' grapefruit. Concentrations of camphene, ethyl hexanoate, alpha-phellandrene, 3-carene, alpha-terpinene, p-cymene, and limonene were higher in pitted white `Marsh' grapefruit than in those of non-pitted fruit. In `Fallglo' tangerines, higher concentrations of limonene and citronellal were found in pitted fruits than in non-pitted fruit. In peel samples of grapefruit, seven different volatiles (methanol, ocimene, citronellyl acetate, alpha-copaene, trans-caryophyllene, alpha-humulene and valencene) were significantly higher in pitted peel than in non-pitted grapefruit peel. Volatiles, such as limonene could be used to predict peel disorders of white `Marsh' grapefruit and `Fallglo' tangerines during storage.

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Huating Dou

The effects of grapefruit cultivar and coating type on chilling injury (CI) incidence were examined. The shellac coating widely used for exported citrus resulted in the lowest CI incidence in white `Marsh' grapefruit stored for 2 months at 4 °C and 92% ± 3% relative humidity compared with nonwaxed fruit or fruit waxed with either carnauba or polyethylene waxes. The order of coating performance for reducing CI was shellac > carnauba > polyethylene > nonwaxed fruit. For `Flame' little difference of coating type on CI was detected after 2 months of storage. Overall, CI incidence was high in fruit of the cultivars harvested from September to December, low in February, and high again after March but was generally higher in white `Marsh' seedless grapefruit than `Ruby Red', `Rio Red', or `Flame'. However, little difference of cultivar on CI incidence was found among the `Ruby Red', `Rio Red', and `Flame' grapefruit except the October harvest in which CI was higher in `Ruby Red' than in `Rio Red' and `Flame' grapefruit. These studies suggest that the coating and cultivar should be considered in the postharvest management of CI in commercial packing.

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Huating Dou* and Gary A. Coates

Influence of 1-MCP application in citrus fruit juice color and vitamin C concentration was determined for `Fallglo' tangerines, `Valencia' oranges, and white `Marsh' grapefruit. MCP was applied at 500 μL·L-1 for `Fallglo', and 1000 μL·L-1 for `Valencia' oranges and `Marsh' grapefruit at 75 °F for 7 hours in a container of 3' × 3' × 3.5' dimension. After three months storage at 40 °F and 93% relative humidity, vitamin C concentration in juice (mg/100 mL) was higher in MCP treated than non-treated `Valencia' oranges (37.1 vs. 30.6) and `Fallglo' tangerines (26.9 vs. 24.0). No difference was found in vitamin C concentration from `Marsh' grapefruit juice either treated (27.9) or non-treated (28.7) with MCP. Forty percent of vitamin C concentration was lost from one month after packing to the third month in storage for white `Marsh' grapefruit. Vitamin C loss was much slower for tangerines in comparison to grapefruit in postharvest. Juice color was not influenced by the MCP application for `Valencia' oranges while Hue and Chroma were improved in treated fruits for `Fallglo' tangerines and `Marsh' grapefruit compared to non-treated fruits. Applying MCP before degreening reduced vitamin C degradation 6 weeks after packing but not at 12 weeks for `Fallglo' tangerines. However, fruit color was improved at 6 and 12 weeks of storage. These results are important for postharvest quality management of citrus fruit and juice.

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Huating Dou and Fred G. Gmitter

A new mandarin cultivar currently designated as selection LB8-9 [‘Clementine’ mandarin (Citrus reticulata) × ‘Minneola’ tangelo, Duncan grapefruit (Citrus paradisi) × Dancy tangerine (C. reticulata)], soon to be released by the University of Florida, Citrus Research and Education Center, Lake Alfred, has been evaluated for postharvest fruit quality and consumer acceptance. Comparisons were made with ‘Sunburst’ and ‘Minneola’ mandarins, which overlap the early and late LB8-9 maturity season, respectively. LB8-9 and ‘Sunburst’ fruit stored 2 weeks at 70 °F developed similar decay percentages (35% to 37%), while ‘Minneola’ showed only 16% decay. Postharvest pitting incidence was zero in LB8-9 and ‘Minneola’ and 3% in ‘Sunburst’ stored at 70 °F and 92% to 96% relative humidity (RH). At the same storage conditions, LB8-9 and ‘Sunburst’ developed better fruit peel color (hue = 60) in comparison with the ‘Minneola’ (hue = 65) mandarin. No differences were found in fruit external peel color (hue angle), chilling injury, or decay among three cultivars stored at 40 °F after 6 weeks. However, juice color was the best in ‘Sunburst’ as indicated by the highest color numbers (44), followed by LB8-9 (40) and ‘Minneola’ (38). Wax-formulation studies indicated that carnauba wax was the best formulation for coating LB8-9 because of low decay incidence, weight loss, and good color. No difference was found in fruit taste panels at day 6 after packing, while a better score of acceptance in the fruit taste panel was recorded for LB8-9 than ‘Minneola’ after 50 d of storage at 40 °F and 92% to 96% RH. LB8-9 fruit had a higher soluble solids concentration [SSC (14.0)] and acid (1.12) than ‘Minneola’ or ‘Sunburst’ mandarins, both having a SSC and acid lower than 11.5 and 0.86, respectively. Sucrose concentration was noticeably higher in the new cultivar (7.14 g/100 mL) than in ‘Minneola’ (5.27 g/100 mL) or ‘Sunburst’ (6.10 g/100 mL). Vitamin C concentration was 42.43 mg/100 mL for the new cultivar, which was considerably higher than ‘Minneola’ (23.27 mg/100 mL) or ‘Sunburst’ (26.25 mg/100 mL). Overall, LB8-9 has good potential as a new fresh fruit for the consumer, and no serious problems were noted with typical postharvest handling.

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Huating Dou and Peter D. Petracek

`Fallglo' is an early season variety of tangerine that has become known among citrus packers for its susceptibility to postharvest peel disorders. Among these disorders is postharvest pitting, a disorder characterized by the collapse of the peel during the storage of waxed fruit at room temperature. In this study, the effects of wax application on selected postharvest storage characteristics were evaluated.

Fruit were either not waxed or waxed with carnauba-, polyethylene-, or shellac-based waxes obtained from four suppliers of commercial citrus coatings and were stored at 21°C. In general, waxing reduced weight loss and improved shine. Waxing with shellac-based waxes significantly decreased internal O2 levels (5% vs. 19% for non-waxed fruit) and increased internal CO2 (6% vs. 2% for non-waxed fruit) and ethanol levels. Waxing with shellac-based waxes also significantly reduced post-packing degreening and stimulated pitting. Waxing with more gas-permeable coatings (carnaubaand polyethylene-based waxes) resulted in less internal gas modification than that of the shellac-based treatments, and low incidences of pitting. Controlled atmosphere studies showed that low (4%) O2, rather than high (8%) CO2, inhibited post-packing degreening and stimulated pitting.

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Huating Dou, Mohamed A. Ismail and Peter. D. Petracek

The effect of clipping vs. pulling, wax application, storage temperature, and fruit size on Stem End Rind Breakdown (SERB) of Valencia oranges was studied in four experiments during the 1998–1999 and 1999–2000 seasons. For harvesting methods, clipping reduced SERB rate of Valencia oranges over pulling from 10.2% to 5.9%. Wax application increased fruit SERB compared to non-waxed fruit. However, there was no consistent difference in effect on SERB incidence between shellac and carnauba waxes in all studies. Small fruit (size 100#) tended to be associated with high incidence of SERB, whereas large fruit (size 64#) were less susceptible to SERB of Valencia oranges. The most significant factor that influenced SERB incidence was storage temperature. Fruit stored at 70 °F had 23% and 96% SERB if fruit were examined in the 2nd and 8th weeks after packing; whereas 0.5% and 2% SERB was found if fruit were stored at 45 °F and examined at the same times. The effect of the above treatments on fruit peel anatomy and postharvest physiological behavior will also be discussed.

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Huating Dou, Peter Petracek, Mohamed Ismail, Ashok Alva and David Calvert

Effects of N, K, and water relation on the incidence and severity of postharvest pitting in white grapefruit were evaluated in two field experiments. In the first experiment, a factorial combination of 3 N (56, 168, and 336 kg·ha–1) and 3 K (52, 156, and 312 kg·ha–1) rates were used with three broadcast applications per year. In the second experiment, there were two irrigation regimes (at 30% and 60% depletion of available soil moisture, ASM, content) with three subtreatments of variable N and K rates (Kg·ha–1) at 56: 52; 112: 104, and 336: 312 kg·ha–1. The fruit were harvested three times each season, waxed with shellac wax, and stored at 70°F for evaluation of pitting. The pitting incidence was lower at the optimal N and K rates than that at the low or high rates. The irrigation at 30% ASM significantly reduced pitting incidence. The higher incidence of pitting was found in an area in the grove with higher water table. This study suggested that effects of water may play an important role on peel physiology and pitting.

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Peter D. Petracek, Lymari Montalvo, Huating Dou and Craig Davis

The morphology and etiology of postharvest pitting of `Fallglo' [Bower citrus hybrid (Citrus reticulata Blanco × C. reticulata Blanco × C. paradisi Macf.) × Temple (C. reticulata Blanco × C. sinensis L.)] peel were determined. The disorder was characterized by scattered collapse of the flavedo that resulted from necrosis of cells within and enveloping the oil glands. In severe cases, damage occurred in epidermal and hypodermal cells above collapsed oil glands and surrounding vascular tissues, but cells between oil glands were often undamaged. Pitting was caused by storing waxed fruit at high temperature (≥15.5 °C), but was not affected by ethylene exposure during degreening. Fruit coated with commercially available shellac- and polyethylene-based waxes pitted more than fruit coated with carnauba-based waxes. Pitting was controlled by not coating the fruit with wax or storing the fruit at low temperature (4.5 °C) within hours after wax application.

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Mark A. Ritenour, Ed Stover, Brian J. Boman, Huating Dou, Kim D. Bowman and William S. Castle

Rootstock significantly affected the development of stem-end rind breakdown (SERB) on `Valencia' and navel oranges (Citrus sinensis), but not `Ray Ruby' grapefruit (C. paradisi) or `Oroblanco' (C. grandis × C. paradisi), and affected postharvest decay on navel orange, `Ray Ruby' grapefruit, `Oroblanco' and one of two seasons (2002) on `Valencia' orange. In `Valencia' and navel oranges, fruit from trees grown on Gou Tou (unidentified Citrus hybrid) consistently developed low SERB. `Valencia' oranges on US-952 [(C. paradisi × C. reticulata) × Poncirus trifoliata] developed high levels of SERB in both years tested. Relative SERB of fruit from other rootstocks was more variable. Navel oranges, `Ray Ruby' grapefruit, and `Oroblanco' fruit from trees on Cleopatra mandarin (C. reticulata) rootstock consistently developed relatively low levels of decay, and in navel this level was significantly lower than observed from trees on all other rootstocks. In three of five trials we observed significant differences between widely used commercial rootstocks in their effects on postharvest SERB and/or decay. Given the expanding importance of sales to distant markets, it is suggested that evaluations of quality retention during storage be included when developing citrus rootstocks and scion varieties for the fresh market.

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Mark A. Ritenour, Robert R. Pelosi, Michael S. Burton, Eddie W. Stover, Huating Dou and T. Gregory McCollum

Studies were conducted between November 1999 and April 2003 to evaluate the effectiveness of compounds applied preharvest for reducing postharvest decay on many types of fresh citrus (Citrus spp.) fruit. Commercially mature fruit were harvested two different times after the compounds were applied, degreened when necessary, washed, waxed (without fungicide), and then stored at 50 °F (10.0 °C) with 90% relative humidity. Compared to control (unsprayed) fruit, preharvest application of benomyl or thiophanate-methyl resulted in significantly (P < 0.05) less decay of citrus fruit after storage in nine out of ten experiments, often reducing decay by about half. In one experiment, pyraclostrobin and phosphorous acid also significantly decreased total decay by 29% and 36%, respectively, after storage compared to the control. Only benomyl and thiophanate-methyl significantly reduced stem-end rot (SER; primarily Diplodia natalensis or Phomopsis citri) after storage, with an average of 65% less decay compared to the control. Though benomyl significantly reduced anthracnose (Colletotrichum gloeosporioides) in two of four tests with substantial (>20%) infection and phosphorous acid significantly reduced it once, thiophanate-methyl did not significantly reduce the incidence of anthracnose postharvest. The data suggests that preharvest application of thiophanate-methyl may reduce postharvest SER and total decay similar to preharvest benomyl treatments.