Non-chilling Temperatures Research Articles

Changes in quality and phenolic antioxidants in dark purple American eggplant ( Solanum melongena L. cv. Lucía) as affected by storage at 0 °C and 10 °C

Many beneficial effects associated with fruit and vegetable consumption are related to the presence of antioxidants, which could be greatly affected by postharvest storage conditions. Eggplants or aubergines ( Solanum melongena L.) are among the top vegetables in terms of antioxidant content. In this work, we evaluated the effect of two postharvest temperature regimes on deterioration and antioxidants of dark purple American eggplants (cv. Lucía). Fruit were stored at 0 or 10 °C for 0, 3, 5, 10 or 14 d and weight loss, electrolyte leakage, chilling injury, and pulp browning were evaluated. We also followed DPPH and Folin–Ciocalteu reacting substances and the content of chlorogenic and quinic acid by HPLC. Although weight loss was reduced in fruit held at 0 °C, higher electrolyte leakage and chilling injury manifested as surface scalds and pulp browning were found. Antioxidants (AOX) measured with the DPPH radical and with the Folin–Ciocalteu reagent increased during the first 3 d of storage at 0 °C, but afterwards significant degradation was found. In contrast, a gradual but continuous accumulation of AOX was detected in fruit stored at 10 °C. The slow rate in the reaction between DPPH and eggplant samples suggested that the main changes during postharvest storage were due to modifications in phenolic compounds. The major phenolic detected by HPLC was chlorogenic acid (ChA), an ester between caffeic (CA) and quinic acids (QA), which accumulated in fruit maintained at 10 °C, increasing by 60% after 14 d of storage. No free CA was found at any storage temperature or time, suggesting that its biosynthesis is activated simultaneously with the production of ChA. Free QA showed minor changes at 0 °C as pulp lightness decreased, indicating that ChA rather than CA may be the main substrate for browning reactions. Changes in eggplant fruit antioxidants during storage at chilling and non-chilling temperatures are discussed.

Temperature conditioning alters transcript abundance of genes related to chilling stress in ‘Marsh’ grapefruit flavedo

Grapefruit ( Citrus × paradisi) develop symptoms of chilling injury (CI) if held at temperatures below about 10 °C. Conditioning grapefruit at a low, but non-chilling (16 °C) temperature prior to storage at a chilling temperature reduces the development of CI symptoms. Changes in transcript abundance for a number of genes have been correlated with chilling stress in citrus fruit. We tested the hypothesis that conditioning affects transcript abundance of genes related to chilling stress in grapefruit. Grapefruit were harvested from a commercial grove in Florida in September and divided into two groups; one group was placed immediately at 5 °C (non-conditioned, NC); the second group was placed at 16 °C for 1 week (conditioned, C) and then transferred to 5 °C. Symptoms of CI were visible on NC and C fruit following 14 d at 5 °C, but were consistently more severe on NC than C fruit. Storage at 5 °C caused increases in abundance of transcripts for 1-aminocyclopropane-1-carboxylate oxidase (ACO), galactinol synthase, a chilling-induced oxygenase, and a temperature-induced lipocalin, consistent with previous reports. Levels of these transcripts were lower in C than in NC fruit during storage at 5 °C, but this pattern did not persist following transfer to 20 °C. Levels of transcripts for catalase, a metallothionein-like protein, a lipid transfer protein, a stress-responsive zinc finger protein, and a citrus low temperature inducible protein were consistently higher in C than NC fruit during storage at 5 °C. Our results show that conditioning increases chilling tolerance in grapefruit and demonstrates that abundance of transcripts of a number of genes related to chilling stress is affected by conditioning. This suggests a potential quantitative relationship between gene expression and conditioning induced chilling tolerance. We cannot say, however, that these changes are related to chilling tolerance per se; they may only reflect the difference between chilling-sensitive and chilling-tolerant fruit.

Quality Attributes Limiting Snap Bean (Phaseolus vulgaris L.) Postharvest Life at Chilling and Non-chilling Temperatures

‘Opus’ and ‘Leon’ snap beans were harvested, hydrocooled, held for 2 to 7 days at five temperatures and evaluated for quality attributes. The objectives of this work were to obtain quality curves at chilling and non-chilling temperatures, identify for each temperature which quality attributes limit snap beans marketability, and determine the remaining compositional value at the point the snap beans had reached the minimum acceptable quality for sale. Results from this study showed that temperature had a significant effect on the shelf life and overall quality of snap bean. Snap beans stored at temperatures higher than 10 °C were less green, softer and more shriveled, had higher weight loss, and lower acidity, soluble solids, ascorbic acid, and chlorophylls contents than those stored at lower temperatures. When stored at 1, 5, and 10 °C, ‘Leon’ snap beans developed chilling injury (CI), whereas no visual symptoms were noticeable in ‘Opus’ snap beans. Although CI might have indirectly affected the quality of ‘Leon’ snap beans, it was not considered a sensory quality-limiting factor. Overall, weight loss was the first non-sensory quality attribute to reach the limit of acceptability, whereas firmness was the first sensory quality attribute, followed by color, to reach the limit of acceptability and therefore limited the shelf life of ‘Opus’ and ‘Leon’ snap beans cultivars. As a result of excessive water loss and accelerated softening, shelf life of both snap bean cultivars was relatively short, ranging from 1 to 3.5 days, depending on the temperature and cultivar. Furthermore, the compositional value was considerably reduced at the point of poor sensory quality. The high weight loss obtained for beans stored at all temperatures suggests that the use of a film wrap may help create a high relative humidity and therefore reduce water loss, maintain better overall quality, and extend the shelf life of snap beans. Overall, maximum shelf life and best quality were obtained when ‘Opus’ and ‘Leon’ snap beans were stored at 10 °C.

Occurrence of chilling injury in fresh-cut ‘Kent’ mangoes

For best visual quality retention of fresh-cut fruits, the preferred storage temperature is never higher than 5 °C, which is considered a chilling temperature for chilling sensitive tropical fruit like mango. Changes in visual and compositional attributes, aroma volatile production, respiration rate, and electrolyte leakage were evaluated in whole and fresh-cut partially ripe ‘Kent’ mangoes stored for 10 d at chilling (5 °C) and non-chilling (12 °C) temperatures in order to determine if fresh-cut mangoes are subject to chilling injury at their typical handling temperature. The experiment was conducted twice during two Florida mango seasons, with fruit from two different sources. Results from the two harvests were significantly different and therefore were analyzed separately. Visual quality degradation was faster at 12 °C than at 5 °C, and limited the shelf-life of the fresh-cut mangoes to 3–4 d at 12 °C versus 5–6 d at 5 °C. Soluble solids content did not differ among whole fruit or fresh-cut slices stored at either chilling or non-chilling temperatures, but respiration rate, pH, and total ascorbic acid were all lower and titratable acidity was higher in both the fresh-cut slices and whole fruit stored at 5 °C compared with storage at 12 °C. Subjective evaluation indicated that aroma intensity declined more during storage of fresh-cut slices at 5 °C than at 12 °C, and the aroma volatiles acetaldehyde, ethyl acetate, and ethyl butyrate were found to be significantly reduced in the slices stored at 5 °C, but only in the second harvest; production of alcohols (methanol and ethanol) was also lower in samples stored at 5 °C. Although electrolyte leakage was higher in fresh-cut slices than in whole fruit, no conclusion could be made regarding the effect of storage temperature. It is unclear whether the storage duration at 5 °C was sufficiently long to cause chilling injury in fresh-cut mango slices since no visual symptoms developed in whole fruit. However, lower ascorbic acid content, higher titratable acidity, reduction of volatiles, and increased softening of whole fruit at 5 °C versus 12 °C, which are all indicative of CI, suggest that the fresh-cut mango slices did experience chilling stress.

Morphological and ultrastructural changes in peel of ‘Navelate’ oranges in relation to variations in relative humidity during postharvest storage and development of peel pitting

‘Navelate’ orange fruit are prone to develop postharvest peel pitting at non-chilling temperatures, also referred to as rind breakdown, a blemish seriously affecting external fruit quality. Changes in the storage relative humidity (RH), in particular transfer of dehydrated fruit to high RH, have been shown to induce and aggravate peel pitting. In this study, we have examined morphological and structural changes, and its relation to water potential ( Ψ W), in flavedo and albedo of ‘Navelate’ fruit exposed to postharvest storage conditions inducing rind breakdown. Cryo-scanning electron microscopy (SEM) observations revealed no signs of cell disruption or collapse in epidermal and flavedo cells from fruit stored up to 1 month at 95% RH. Under low RH, flavedo became less compacted and outer layers were translucent. Albedo cells dehydrated by storage at 45% RH became progressively compacted, forming clusters of amorphous and flattered cells, in which the typical spongy structure of the albedo was gradually lost. After prolonged dehydration, cracks and fractures in the wall of albedo cells were evident. Normal structure and morphology of albedo cells were not recovered after fruit transfer from low to high RH, even after prolonged storage at high RH. Injuries in albedo cells and the connecting arms were detected soon after the shift in postharvest RH and progressively increased in number and length. Associated with these morphological alterations, important changes in water potential of flavedo and albedo cells were also noted, that were more pronounced in flavedo than in albedo. Collectively, the results suggest that changes in postharvest RH produced water content adjustment and water movement within the peel tissue that may underlie the morphological and structural alterations accompanying postharvest rind breakdown in ‘Navelate’ orange fruit.

Variation in water, osmotic and turgor potential in peel of ‘Marsh’ grapefruit during development of postharvest peel pitting

Postharvest peel pitting at non-chilling temperatures is a physiological disorder that affects fruit of several citrus cultivars worldwide. Although causes of the disorder are not fully understood, evidence indicates that altered water relations in fruit peel is a major factor inducing peel pitting during postharvest storage. In this work, the effect of commercial packingline and manual processing and subsequent storage under low and high RH regimes on water, osmotic and turgor potentials in three layers of ‘Marsh’ grapefruit peel (flavedo and internal and external albedo) was investigated. At the end of the storage period at 45% RH, peel water potential was lower in fruit processed on a commercial packingline compared to those processed manually. Transfer of dehydrated fruit to 95% RH increased water potential of flavedo at the expense of albedo cell layers, which underwent subsequent water loss. Water potential of flavedo in packingline-processed fruit did not recover by transferring to high RH. Osmotic potential in peel tissues did not change as significantly as water potential. As a consequence, turgor pressure decreased in all three peel tissues of fruit stored at 45% RH, this decrease being more pronounced in packingline-processed fruit. In manually wax-coated fruit stored at 45% RH, transfer to 95% RH induced a recovery of turgor potential. In contrast, turgor pressure did not recover in packingline-processed fruit similarly treated, and severe peel pitting developed. The results suggest that the inability to properly carry out water adjustments after prolonged water stress leads to cell collapse and peel damage. Together, the data link alterations in water, osmotic and turgor potential in flavedo and albedo with the induction of postharvest peel pitting in citrus fruit.

EFFECT OF WAX APPLICATION ON THE QUALITY, LYCOPENE CONTENT AND CHILLING INJURY OF TOMATO FRUIT

ABSTRACT Waxed and nonwaxed mature green tomato fruits were stored at 12C (nonchilled) or 5C (chilled) for 5, 10, 15 and 20 days before being transferred to 22C for 3, 6, 9 and 12 days, were evaluated for weight loss, chemical composition, skin color, chilling injury (CI) index and pigment content. Waxed fruits showed a delay in weight loss, color development and ripening. The sensitivity of tomato fruit to CI was reduced in waxed fruits, which showed a delay in the appearance of symptoms. A delay in chlorophyll degradation and lycopene synthesis was observed as a result of the use of wax and low temperature. Waxing of tomato fruits allowed their storage at temperatures below critical reducing CI sensitivity and maintaining quality giving more time for marketing. PRACTICAL APPLICATIONSNowadays, local tomato producers use wax on fruits as an everyday practice to carry postharvest fungicides and to improve brightness. They store tomato fruits at nonchilling temperature (12C) because lower temperatures would cause chilling injury and irregular ripening. In this way, it is interesting that waxing tomato fruits allow reducing their storage temperature, protecting them from chilling injury and maintaining their quality and correct color change and ripening; thereby producers and sellers have more days to position their fruits with no extra cost.

β-1,3-Glucanase gene expression as a molecular marker for postharvest physiological disorders in citrus fruit and its hormonal regulation

The aim of this work was to understand whether a CrglcQ gene, encoding an acidic class III β-1,3-glucanase isolated from citrus flavedo, may serve as a biochemical marker for the development of postharvest physiological disorders; and whether this gene is regulated by ethylene and abscisic acid (ABA). We have examined the changes in the accumulation of the CrGlcQ mRNA in the flavedo of ‘Navelate’ oranges, a variety prone to develop brown non-depressed areas in response to chilling, and in the flavedo of its ABA-deficient mutant ‘Pinalate’, a variety tolerant to chilling but very susceptible to non-chilling peel pitting, during fruit storage at chilling (2 °C) and non-chilling temperatures (12 °C). The levels of the CrGlcQ transcript increased transiently in fruit exposed to postharvest conditions favoring both chilling and non-chilling peel disorders, such an increase being evident even in the fruit of the ABA-deficient mutant ‘Pinalate’ in which ABA does not increase in response to stress conditions. Such increases paralleled those in ethylene production and preceded the appearance of visible symptoms of damage. Moreover, we examined changes in gene expression in ‘Fortune’ mandarins held under water stress conditions (20 °C and 55–60% RH) that did not cause any peel damage, and found that the increase in ABA was not mirrored by the changes in CrglcQ mRNA accumulation. The results revealed that changes in CrglcQ gene expression are linked to the development of postharvest peel disorder, in spite of being induced by different environmental conditions, and indicated that this gene might be regulated by ethylene but not by the ABA.

QUALITY CURVES FOR MANGO FRUIT (CV. TOMMY ATKINS AND PALMER) STORED AT CHILLING AND NONCHILLING TEMPERATURES

ABSTRACT “Tommy Atkins” and “Palmer” mangoes were harvested medium‐ripe held for 7–20 days at five different temperatures and evaluated for quality attributes. The objective of this work was to obtain quality curves at chilling and nonchilling temperatures and to identify, for each temperature, which quality factors limit mango marketability. Chilling injury and increased fruit softness were the limiting quality factors for mango stored at 2 and 5C. Softening of the fruit, changes in color and development of decay were the limiting quality factors for mango stored at 12, 15 and 20C. Prediction of mango shelf life calculated from the data reported in the literature is not precise unless the characteristics of the fruit and environmental factors involved are well known. The curves obtained from quality evaluations for each temperature showed that a single quality attribute cannot be used to express loss of quality of mango over the normal physiological range of temperatures.

EVALUATION OF COMMERCIAL ALTERNATIVES TO REDUCE POSTHARVEST PITTING OF ORGANICALLY GROWN ZUCCHINI AND CUCUMBER

Postharvest pitting in organic cucumber and zucchini is a major problem in the market chain. Losses due to postharvest pitting occur either at the production site, packinghouse, distribution center or retail site, especially when sensitive commodities are shipped to distant markets. Our goals were to determine the origin of pitting in cucumbers and zucchini, and to identify feasible options that could be commercially incorporated to minimize this quality defect. We examined relative humidity, and associated water loss as potential triggers of the development of pitting. In commercial conditions we observed development of pitting as quickly as 6 h after harvest, particularly in zucchini. Postharvest pitting was eliminated with high relative humidity in the patio of the packinghouse and when the product was bagged. We also studied the effect of Biocoat, a beeswax base organic certified wax, on pitting. Zucchini and cucumber coated with the beeswax product showed a significant reduction of over 50% when stored for more than 7 days. This study revealed that postharvest pitting at non-chilling temperatures in zucchini and cucumber is directly associated with rapid water loss during the first few hours after harvest. It was also shown that bagging and beeswax-base coating eliminate or delay the appearance of pitting during postharvest storage. These results have implications for the organic vegetable industry.

Modified and controlled atmosphere storage of subtropical crops

Purpose of the review: This article addresses the use of modified atmosphere (MA) and controlled atmosphere (CA) storage for the preservation and maintenance of the postharvest quality of subtropical fruits. There have been great technological advances, especially in improving the quality and shelf-life of fresh-cut produce. Thus, this review focuses on MA and CA technologies that are either commercially available or under investigation. Recent findings: Under MA and CA conditions, the respiration rate of the fruit is decreased and, as a direct effect, the consumption of respiration substrates such as organic acids and sugars is retarded, and the growth of micro-organisms is suppressed. Therefore, MA and CA are helpful in maintaining the quality of many subtropical fruits. Limitations: When using these technologies, careful attention must be paid to the survival and growth of pathogenic organisms in the enclosed conditions due to high relative humidity, particularly at warm non-chilling temperatures. Directions for future research: More research is needed on the microbiological safety of fresh-cut subtropical fruits and the effect of antimicrobial films on various intact and fresh-cut subtropical commodities. Interaction between various gas concentrations, both MA and CA, the development of pathogenic micro-organisms and finding better film types for different species and cultivars of subtropical fruits also merit further research.

Optimal Low-pressure Conditions for Long-term Storage of Fresh Commodities Kill Caribbean Fruit Fly Eggs and Larvae

U.S. regulations prevent importation of fresh horticultural commodities that have not received an approved quarantine treatment assuring 99.999% (Probit 9) mortality of potentially invasive insect pests. Because imported mangoes (Mangifera indica) are likely to be infested by the caribbean fruit fly (Anastrepha suspensa) and other tropical fruit flies in the Americas, such as the mexican fruit fly (A. ludens), guava fruit fly (A. striata), inga fruit fly (A. distincta), south american fruit fly (A. fraterculus), sapote fruit fly (A. serpentina), and the west indian fruit fly (A. obliqua), they must be hot-water treated prior to shipment in order to satisfy quarantine requirement. Hot water treatment often damages the fruit, especially if it is not fully mature. Hypobaric [low pressure (LP)] intermodal shipping containers developed by the VacuFresh Corp. preserve fresh commodities, such as horticulturally mature mangoes, far longer than is possible using other technologies. We tested the ability of caribbean fruit fly eggs and larvae to survive simulated optimal hypobaric conditions for shipment of mangoes [15 and 20 mm mercury (Hg), ≥98% relative humidity, 13 °C (the lowest, safe nonchilling temperature)]. Caribbean fruit fly eggs or larvae were maintained on agar media, flushed with one air change per hour at the storage pressure, and shielded with Mylar to prevent radiant heat uptake and limit evaporative cooling. Nearly 98% of the eggs and larvae were killed within 1 week at 15 and 20 mm Hg in nine replicated experiments. All eggs were killed by 11 days with a predicted kill of 99.999% of the eggs by 9.4 days in 15 mm Hg and 10.6 days in 20 mm Hg LP (based on Probit 9 statistical analysis), whereas a substantial number of eggs survived to 14 days at atmospheric pressure (760 mm Hg). Shipment of fresh produce using this technology promises to provide quarantine control while preserving the freshness of fully mature tropical fruits and vegetables.

Carbohydrate Metabolism As Related to High-Temperature Conditioning and Peel Disorders Occurring during Storage of Citrus Fruit

The aim of this research was to understand the involvement of the carbohydrate metabolism in physiological disorders occurring during the postharvest storage of citrus fruit. These disorders, manifested in the rind, depreciate fruit quality and often originate important losses. There has been increasing interest in the use of nonharmful treatments, such as high-temperature conditioning, to avoid citrus peel damage during fruit storage at low temperature in chilling-sensitive cultivars, but their influence in postharvest disorders occurring at nonchilling temperatures and the mechanisms related to them are poorly understood. The data obtained showed that heat conditioning (3 days/37 degrees C) increases the chilling tolerance of cv. Navelate fruit and favored sucrose, but not hexoses, accumulation and its maintenance after the fruit was transferred to low temperature. This effect was related to heat-induced increase in the activities of the sucrose-synthesizing enzymes sucrose phosphate synthase (SPS) and sucrose synthase (SS). Furthermore, sucrose levels and the activities of both enzymes were higher in cv. Pinalate oranges, a chilling-tolerant spontaneous abscisic acid deficient mutant of Navelate. In contrast, carbohydrates appeared not to be involved in the susceptibility of oranges to rind staining, a physiological disorder different from chilling injury, which mainly occurred at a nonchilling temperature (12 degrees C) and was not reduced by heat conditioning. The effect of low temperature in SS and SPS activities was less than that of high temperature, which might be related to the lower changes occurring in sucrose during fruit storage at 2 degrees C.

Study of water transpiration features of sweet pepper using a thermal imaging system and non-destructive quality monitoring during post-harvest storage

Sweet pepper is susceptible to relatively fast quality changes and its quality is influenced strongly by water or mass losses mainly due to transpiration processes during post-harvest. The aim of this study was the investigation of different storage conditions' effect on quality maintenance of pepper using surface thermal imaging, measurement of overall static stiffness and low-mass impact stiffness as non-destructive methods. Post-harvest keeping quality of pepper samples increased and unfavourable quality degradation was prevented under low, non-chilling temperatures together with the use of LDPE-packaging film resulted in high quality and fresh appearance after more than two weeks long storage period.

A comparative study of the postharvest performance of an ABA-deficient mutant of oranges: II. Antioxidant enzymatic system and phenylalanine ammonia-lyase in non-chilling and chilling peel disorders of citrus fruit

Postharvest rind disorders of citrus fruit may be caused by chilling but also by other stress conditions at non-chilling temperatures. The mechanisms involved in the tolerance of citrus fruit to these postharvest physiological disorders and how they are related to each other are not well understood. In the present work, we have examined changes in the activities of the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR), and of phenylalanine ammonia-lyase (PAL), the initial rate-controlling enzyme in phenolic synthesis, in ‘Navelate’ oranges and in its yellow abscisic acid-deficient mutant ‘Pinalate’ in relation to their susceptibility to chilling injury (CI) and to non-chilling peel pitting. ‘Navelate’ oranges developed CI during storage at 2 °C and very slight postharvest non-chilling peel pitting at 12 °C. By contrast, ‘Pinalate’ fruit did not show CI and were more susceptible to non-chilling peel pitting than ‘Navelate’ fruit. No important differences in the activities of the enzymes GR and APX were found in fruit of both phenotypes when stored at 2 °C or 12 °C. By contrast, ‘Pinalate’ fruit, the chilling-tolerant cultivar, had higher CAT activity than ‘Navelate’ oranges during storage at 2 °C, while it was lower at the temperature causing non-chilling peel pitting. PAL activity barely changed in response to cold stress in the mutant but increased in the chilling-susceptible ‘Navelate’ fruit. On the other hand, the increase in PAL occurring in ‘Pinalate’ fruit at 12 °C might be associated with their greater development of non-chilling peel pitting. The overall results indicate that the enzyme PAL might be a good biochemical marker for both chilling-induced superficial scald and non-chilling peel pitting and that CAT may play a role protecting ‘Navelate’ and ‘Pinalate’ fruit from conditions favoring both physiological disorders. In addition, SOD could be involved in the higher tolerance of ‘Navelate’ oranges to develop non-chilling peel pitting.

A comparative study of the postharvest performance of an ABA-deficient mutant of oranges: I. Physiological and quality aspects

We have recently characterized ‘Pinalate’ ( Citrus sinensis L. Osbeck), a yellow abscisic acid (ABA)-deficient mutant derived from the orange ‘Navelate’. In this study we have compared the postharvest performance of fruit of both cultivars stored at 2 and 12 °C to further understand mechanisms underlying chilling injury (CI) and non-chilling peel pitting disorders and whether deficiency in ABA may affect other quality and physiological processes in citrus fruit. The rate of dehydration in ABA-deficient fruit was higher than in its wild type ‘Navelate’. ABA levels in the flavedo of the mutant were about six-fold lower than in its parental. No changes in ABA were observed in fruit of the mutant stored at both 2 and 12 °C, while ABA increased during holding of ‘Navelate’ fruit at 12 °C and decreased at the temperature causing CI. Water, osmotic and turgor potential in the flavedo of freshly harvested fruit of both cultivars were similar and changed differentially in response to storage at 2 and 12 °C. Turgor potential was higher in ‘Pinalate’ than in ‘Navelate’ fruit held at 2 °C, probably by impaired osmotic adjustment. At 12 °C, both water and osmotic potential were lower in the ABA-deficient mutant and as a result, turgor remained constant and similar to that of ‘Navelate’ fruit. The most relevant differential feature associated with fruit quality was the higher susceptibility of ‘Pinalate’ fruit to decay and its higher loss of peel firmness during storage at 12 °C. Interestingly, fruit of the ABA-deficient mutant were more prone to develop peel pitting at non-chilling temperatures than ‘Navelate’, but more resistant to CI, which was manifested as brown non-depressed areas. A transient increase in ethylene production was observed before the appearance of both chilling and non-chilling peel pitting symptoms, suggesting that ethylene may be an indicator of the initial cell damage occurring in both citrus cultivars under postharvest conditions inducing different peel disorders. Under high rates of water loss, ethylene production was markedly enhanced in the ABA-deficient mutant, but not in ‘Navelate’ fruit, indicating that in citrus fruit, ABA may be a negative regulator of water stress-induced ethylene synthesis.

Postharvest Peel Pitting in Citrus Fruit at Nonchilling Temperatures Is Affected by Climatic Factors and Advanced by Changes in Peel Water Status

Several citrus varieties, including `Navel' oranges, `Marsh' grapefruit and `Fallglo' tangerines are prone to develop postharvest peel pitting at nonchilling temperatures. The disorder is characterized by depressions in flavedo that ultimately affect oil glands. Increasing evidence indicates that changes in peel water status during postharvest handling of fruit plays a major role in the appearance of the disorder. Peel pitting was triggered when fruit were transferred from low to high relative humidity (RH) consistently in several citrus growing areas. A transient increase in fruit ethylene production and ABA content was observed within the first 24 hours after transfer from low to high RH. Water potential decreased with storage at low RH in flavedo and albedo, and recovered faster in flavedo than in albedo cells upon transfer to high RH. The differential recovery in water potential between flavedo and albedo is postulated to cause collapse of external albedo layers and pitting. The effect of climatic conditions in the field at harvest was also examined. Harvesting fruit at low RH induced more severe pitting after storage than harvesting at high RH. In addition, increasing hours of low RH storage prior to storage at high RH resulted in increased pitting. The results demonstrate that change in peel water status is a major factor leading to the development of postharvest peel pitting in citrus.

(47) Optimal Low Pressure Conditions for Long-term Storage of Fresh Commodities Kill Caribbean Fruit Fly Eggs and Larvae

U.S. regulations prevent importation of fresh horticultural commodities that have not received an approved quarantine treatment assuring 100% mortality of potentially invasive insect pests. Because imported mangoes are likely to be infested by the Caribbean fruit fly (Anastrepha suspensa Loew) and other tropical fruit flies such as A. ludens Loew, A. striata, A. distincta, A. fraterculus, A. serpentina, or A. oblique, they must be hot-water treated prior to shipment in order to satisfy quarantine requirement. Hot water treatment often damages the fruit, especially if it is not fully mature. Hypobaric (low pressure = LP) intermodal shipping containers developed by the VacuFreshSM Corp. preserve fresh commodities, such as horticulturally mature mangoes, far longer than is possible using other technologies. We tested the ability of over 70,000 Caribbean fruit fly eggs and larvae to survive a simulated optimal hypobaric condition for shipment of mangoes (15 mm Hg, 98% RH, at the lowest, safe non-chilling temperature, 13 °C). A. suspensa eggs or larvae were maintained on agar media, flushed with one air change per hour at the storage pressure, and shielded with Mylar to prevent radiant heat uptake and limit evaporative cooling. Nearly 98% of the eggs and larvae were killed within 1 week at 15 mm Hg in eight replicated experiments. All eggs were killed at that pressure by 11 days, whereas a significant number survived at ambient pressure. Shipment of fresh produce using this technology promises to provide quarantine control while preserving the freshness of fully mature tropical fruits and vegetables.

PHENYLALANINE AMMONIA-LYASE AND ACCUMULATION OF PHENOLIC COMPOUNDS IN THE ETHYLENE-INDUCED TOLERANCE TO RINDSTAINING IN ´NAVELATE´ FRUIT

The orange fruit cultivar 'Navelate' is prone to develop postharvest rindstaining (RS) during storage at non-chilling temperatures. Ethylene has been shown to protect citrus fruit against RS but the mechanisms associated with the ethylene-induced tolerance to this disorder are unknown. In this study we have examined the effect of applying ethylene, before or during holding of 'Navelate' fruit under postharvest conditions inducing RS (22°C, 90-95% RH), on changes in the activity of the enzyme phenylalanine ammonia-lyase (PAL), total phenolic content and fruit quality. PAL activity increased with the development of damage in the albedo and flavedo of fruit maintained under air. Exogenous ethylene treatments, which efficiently reduced RS incidence, increased PAL activity as well as the levels of total phenolic content in the flavedo and in the pulp. However, these levels were not maintained after prolonged storage, either in fruit kept continuously under ethylene or in those transferred to air. The global results indicate that the induction of the enzyme PAL and of subsequent phenylpropanoid compounds may play a role in reducing the development of RS symptoms and might be a part of the mechanisms involved in the beneficial effect of ethylene in protecting citrus fruit against this physiological disorder.

Freezing temperature treatment induces bud dormancy in ‘Granny Smith’ apple shoots

One-year-old, ‘Granny Smith’ apple ( Malus × domestica Borkh.) shoots were selected randomly from commercial orchards in 1999 and 2003, cold stored at temperatures between 1 and 13 °C for varied periods, following a 12/12 h freezing temperature pre-treatment of −1/13 °C (supposedly non-chilling temperatures) for 1 or 2 weeks. The rate of budburst, determined after forcing at 25 °C, was used to follow the progression of bud dormancy. The freezing pre-treatment clearly enhanced (deepened) bud dormancy in all experiments. Clearly definable influences due to the presence of leaves during the pre-treatment were not observed on shoots cold stored at chilling temperatures. Trees were defoliated before leaf drop in late summer/autumn under field conditions by hand (2001) and using a spray containing 3% urea and 1.8% zinc sulphate in 2003. In 2001 the first two hand defoliation dates significantly enhanced dormancy, while in 2003 chemical defoliation had no effect. These data indicate that the leaves are not clearly involved in the perception of factors that are responsible for dormancy induction. As with dormancy release it is possible that the perception of induction factors, i.e. low temperatures, and as shown in these data, freezing temperatures, occurs within the buds themselves.