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Robert K. Prange, Peter A. Harrison, and Jennifer R. DeEll

In a 2-year study, `McIntosh' apples were stored in a CA regime of 4.5% CO2 + 2.5% O2. Within the CA cabinets there were three humidity levels: >75% RH (CaCl2 salt in the chamber), >90% RH (ambient), or >95% RH (distilled water in the chamber). After removal at 4 and 8 months, the fruit were warmed to handling temperatures of 0C, 10C, or 20C and subjected to three levels of impact bruising of 0, 10, or 20 lb with a Ballauf pressure tester with a 1.5 × 1.5-cm tip. The results showed that low-humidity CA storage decreased visible bruising. Although visible shrivel was not observed, the low-humidity treatment may increase the possibility of its occurrence. Respiration, measured as O2 consumption or CO2 production immediately after removal from CA storage, was lowest in low humidity (>75% RH) and highest in ambient humidity (>90% RH) CA storage. The humidity treatments did not affect firmness, soluble solids, titratable acids, or ethylene production. Increasing the temperature during post-storage handling decreased the amount of visible bruising without affecting other variates such as firmness, soluble solids, titratable acids, respiration, or ethylene production.

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Barbara J. Daniels-Lake, Robert K. Prange, and John R. Walsh

In three consecutive years of storage trials, the effects of reduced O2 levels, elevated CO2 levels, and ethylene on the fry color and sugar content [sucrose and reducing sugars (glucose and fructose)] of `Russet Burbank' potato (Solanumtuberosum L.) tubers were evaluated. The potatoes were stored in modified atmosphere chambers and the atmosphere mixtures were supplied from compressed gas cylinders. Fry color and sugar content were assessed at the start of each trial and after several weeks of exposure to the treatment atmospheres. Four 4-week trials were conducted in 2002 and two 9-week trials were conducted in each of 2003 and 2004. No differences in fry color or sugar content attributable to either increased CO2 or decreased O2 were observed, compared with untreated controls, in any year. In the second and third years, only selected treatments were repeated, with or without 0.5 μL·L-1 ethylene. Ethylene alone caused a moderate darkening of fry color and an increase in reducing sugars. However, the fry color and reducing sugar content of tubers exposed to a combination of elevated CO2 and ethylene were considerably darker and higher, respectively, than observed with ethylene alone. No similar interaction between ethylene and O2 level was observed. These results suggest that CO2 promoted ethylene-induced fry color darkening, which may explain the contradictory effects of CO2 on fry color frequently observed by the potato industry. This is contrary to published research on other fruits and vegetables, which has generally shown that CO2 inhibits ethylene action.

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Artur Miszczak, Charles F. Forney, and Robert K. Prange

`Kent' strawberries were harvested at red, pink, and white stages of development, and stored at 15C in the light. Fruit were sampled over a 10-day period and evaluated for volatile production and surface color. Volatile production by red and pink fruit peaked after 4 days of storage. Maximum volatile production by red fruit was 8- and 25-fold greater than maximum production by pink and white fruit, respectively. Aroma volatiles were not detected in the headspace over white berries until 4 days following harvest after which volatile production increased through the tenth day of storage. Changes in the surface color of white berries during postharvest ripening coincided with the production of volatiles. In another experiment, red, pink, and white `Kent' strawberries were stored for 3 days at 10 or 20C in the dark or light. Fruit were then evaluated for volatile production, weight loss, anthocyanin content, and surface color changes. White berries produced volatile esters after 3 days of storage at 20C in the light. Both light and temperature influenced the relative production of the volatiles produced by pink fruit. Fresh weight loss, color change, and anthocyanin content were temperature and light dependent.

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Jennifer R. DeEll, Robert K. Prange, and Dennis P. Murr

Chlorophyll fluorescence, measured using a Plant Productivity Fluorometer Model SF-20 (Richard Brancker Research, Ottawa, Ont.), was evaluated as a rapid and nondestructive technique to detect low O2 and/or high CO2 stress in apples during storage. `Marshall' McIntosh apples were held for 5, 10, 15, 20, or 25 days at 3C in the following four treatments: standard O2 (2.5% to 3%) and low CO2 (<1%); low O2 (1% to 1.5%) and low CO2 (<1%); standard O2 (2.5% to 3%) and standard CO2 (4% to 4.5%); or standard O2 (2.5% to 3%) and high CO2 (11% to 12%). Only 10% of the apples had skin discoloration after 5 days in 1% to 1.5% O2, while 80% developed skin discoloration after 20 days in low O2. Small desiccated cavities in the cortex, associated with CO2 injury, developed in 10% of the apples after 20 days in 11% to 12% CO2. Both 1% to 1.5% O2 and 11% to 12% CO2 for 5 days caused chlorophyll fluorescence [Fv = (P – T)/P] of apple fruit to decrease, as compared to those held in standard atmospheres. Additional exposure time did not significantly affect Fv in either the low-O2 (1% to 1.5%) or high-CO2 (11% to 12%) treatment. The results of this study suggest that chlorophyll fluorescence can detect low-O2 and high-CO2 stress in apples, prior to the development of associated physiological disorders.

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Ali A. Ramin, P. Gordon Braun, Robert K. Prange, and John M. DeLong

Biofumigation by volatiles of Muscodor albus Worapong, Strobel & W.M. Hess, an endophytic fungus, was investigated for the biological control of three postharvest fungi, Botrytis cinerea Pers., Penicillium expansum Link, and Sclerotinia sclerotiorum (Lib) de Bary, and three bacteria, Erwinia carotovora pv. carotovora (Jones) Bergey et al., Pseudomonas fluorescens Migula (isolate A7B), and Escherichia coli (strain K12). Bacteria and fungi on artificial media in petri dishes were exposed to volatiles produced by M. albus mycelium growing on rye seeds in sealed glass 4-L jars with or without air circulation for up to 48 hours. The amount of dry M. albus–rye seed culture varied from 0.25 to 1.25 g·L–1 of jar volume. Fan circulation of volatiles in jars increased efficacy and 0.25 g·L–1 with fan circulation was sufficient to kill or suppress all fungi and bacteria after 24 and 48 hours, respectively. Two major volatiles of M. albus, isobutyric acid (IBA) and 2-methyl-1-butanol (MB), and one minor one, ethyl butyrate (EB), varied in their control of the same postharvest fungi and bacteria. Among the three fungi, IBA killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 40, 25, and 45 μL·L –1, respectively. MB killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 75, 100, and 100 μL·L –1, respectively. EB was only able to kill S. sclerotiorum at 100 μL·L –1. Among the three bacteria, IBA killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 5, 12.5, and 12.5 μL·L–1, respectively. MB killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 100, 75, and 100 μL·L–1, respectively. EB did not control growth of the three bacteria. This study demonstrates the need for air circulation in M. albus, MB, and IBA treatments to optimize the efficacy of these potential postharvest agents of disease control.

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John M. DeLong, Robert K. Prange, Conny Bishop, Peter A. Harrison, and Daniel A.J. Ryan

To determine if postharvest treatments of 1-methylcyclopropene (1-MCP) retard the senescence of highbush blueberries (Vaccinium corymbosum L.) removed from storage, `Burlington' (early) and `Coville' (late) fruit were harvested from four experimental sites and treated for 24 hours at 20 °C with 0 (control), 25 (low), 100 (medium), or 400 (high) nL·L-1 of 1-MCP. All fruit were then stored in a controlled atmosphere of 10-15 kPa O2 and 10 kPa CO2 at -1 to 1 °C for 4, 8, and 12 weeks, followed by a 20 °C shelf-life of up to 20 days. During the shelf-life period immediately after harvest and those following each storage removal, percent marketable fruit (PMF) were calculated daily as: [fruit in good condition]/[total berry number] × 100. Changes in PMF were not affected by 1-MCP treatment; hence, we conclude that 1-MCP at rates up to 400 nL·L-1 does not alter the shelf-life quality of the highbush blueberry cultivars tested.

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John M. DeLong, Robert K. Prange, Jerry C. Leyte, and Peter A. Harrison

HarvestWatch is a new chlorophyll fluorescence (F)-based technology that identifies the low-oxygen threshold for apple (Malus × domestica) fruit in dynamic low-O controlled atmosphere (DLOCA) storage environments [e.g., <1% oxygen (O2)]. Immediately following harvest, `Cortland', `Delicious', `Golden Delicious', `Honeycrisp', `Jonagold' and `McIntosh' fruit were cooled and loaded into 0.34 m3 (12.0 ft3) storage cabinets. A static controlled atmosphere (CA) regime of 1.5% O2, 1.5% carbon dioxide (CO2) and 3 °C (37.4 °F) [0 °C (32.0 °F) for `Delicious' and `Golden Delicious'] was established for the control fruit, while the low-O2 threshold was identified by a spike in the fluorescence parameter, Fα, as the O2 levels in the DLOCA cabinets were lowered below 1%. The DLOCA storages were then maintained at O2 levels of 0.1% to 0.2% above the threshold value for each cultivar, which returned Fα to prethreshold signatures. Quality measurements following 5 to 9 months of storage and a 7-day shelf life of 20 °C (68.0 °F), showed that the HarvestWatch fruit were generally firmer, had no incidence of superficial scald in `Cortland' and `Delicious' apples, and did not accumulate fermentative volatile compounds. The HarvestWatch system permits rapid, real-time measurements of the status of stored apple fruit in ultra low-O2 environments without the inconvenience of breaking the room's atmosphere. Our results indicate that HarvestWatch facilitates what may be the highest possible level of fruit quality retention in long-term, low-O2 apple storage without the use of scald-controlling or other chemicals before storage.

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Robert K. Prange, John M. DeLong, Peter A. Harrison, Jerry C. Leyte, and Scott D. McLean

A new chlorophyll fluorescence (F) sensor system called FIRM (fluorescence interactive response monitor) was developed that measures F at low irradiance. This system can produce a theoretical estimate of Fo at zero irradiance for which we have coined a new fluorescence term, Fα. The ability of Fα to detect fruit and vegetable low-O2 stress was tested in short-term (4-day) studies on chlorophyll-containing fruit [apple (Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.), pear (Pyrus communis L.), banana (Musa ×paradisiaca L.), kiwifruit (Actinidia deliciosa C.S. Liang & A.R. Ferguson), mango (Mangifera indica L.), and avocado (Persea americana Mill.)] and vegetables (cabbage (Brassica oleracea L. Capitata Group), green pepper (Capsicum annuum L. Grossum Group), iceberg and romaine lettuce (Lactuca sativa L.)). In all of these fruit and vegetables, Fα was able to indicate the presence of low-O2 stress. As the O2 concentration dropped below threshold values of 0 to 1.4 kPa, depending on the product, the Fα value immediately and dramatically increased. At the end of the short-term study, O2 was increased above the threshold level, whereupon Fα returned to approximately prestressed values. A 9-month study was undertaken with `Summerland McIntosh' apple fruit to determine if storing the fruit at 0.9 kPa O2, the estimated low O2 threshold value determined from Fα, would benefit or damage fruit quality, compared with threshold + 0.3 kPa (1.2 kPa O2) and the lowest recommended CA (1.5 kPa O2). After 9 months, the threshold treatment (0.9 kPa) had the highest firmness, lowest concentration of fermentation volatiles (ethanol, acetaldehyde, ethyl acetate) and lowest total disorders. Sensory rating for off-flavor, flavor and preference indicated no discernible differences among the three treatments.

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John M. DeLong, Robert K. Prange, Peter A. Harrison, R. Andrew Schofield, and Jennifer R. DeEll

A final harvest window (FHW), expressed as Streif Index coefficients [firmness/(percentage soluble solids concentration × starch index)], was developed for identifying maximum fruit quality for strains of `McIntosh', `Cortland', and `Jonagold' apples (Malus ×domestica Borkh.) following 8 months of controlled-atmosphere (CA) storage. The Streif Index was calculated during nine preharvest (twice per week) intervals and four weekly harvests over three seasons. The relationship between Streif Index (dependent variable) and day of year (independent variable) of the preharvest and harvest samples was then derived by negative first-order linear regression equations that had parameter estimate (b1) probability values ≤0.0001 for all of the strains. Apples from the four harvest periods were stored in standard CA storage for 8 months and then subjected to a 7-day shelf-life test at 0 °C followed by 5 days at 20 °C. Poststorage quality data were categorized and combined to produce an overall fruit quality rating scale. For each strain, the final harvest (i.e., day of year) was identified as that which directly preceded at least a 10% drop in the poststorage fruit quality rating compared with the first harvest rating. The FHW, expressed as Streif Index coefficients via the regression of Streif Index (Y) on day of year (X), was then calculated as the 3-year final harvest mean with the upper and lower window limits being determined by the standard deviation of the mean. The lower to upper FHW boundaries ranged from 4.18 to 5.34, 4.12 to 5.46, 4.51 to 5.68, 5.23 to 5.99, and 1.38 to 2.34 for Redmax, Marshall and Summerland `McIntosh', Redcort `Cortland' and Wilmuta `Jonagold', respectively. The practical utility of the Streif Index method lies in the ease with which apple fruit maturity at harvest can be evaluated for its suitability for long-term CA storage.

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Robert K. Prange, Ali A. Ramin, Barbara J. Daniels-Lake, John M. DeLong, and P. Gordon Braun

Fewer postharvest technologies are available for use on organic than conventional fruits and vegetables. Even though biopesticides are perceived as likely candidates for postharvest use on organic produce, only some biopesticides will be approved as organic compounds for various reasons. An example is the definition of a biopesticide used by regulatory agencies such as the EPA which includes compounds that will not be considered organically acceptable. Fortunately, there are other existing or new technologies that could be acceptable on organic fruits and vegetables. Some examples are hot water immersion treatment or a hot water rinsing and brushing, new innovative controlled atmosphere techniques, alternative sprout control agents, naturally occurring volatiles and biofumigants. More research is needed on each of these technologies, both singly and in combination with each other.