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Sastry Jayanty, Jun Song, Nicole M. Rubinstein, Andrés Chong, and Randolph M. Beaudry

The temporal relationship between changes in ethylene production, respiration, skin color, chlorophyll fluorescence, volatile ester biosynthesis, and expression of ACC oxidase (ACO) and alcohol acyl-CoA transferase (AAT) in ripening banana (Musa L. spp., AAA group, Cavendish subgroup. `Valery') fruit was investigated at 22 °C. Ethylene production rose to a peak a few hours after the onset of its logarithmic phase; the peak in production coincided with maximal ACO expression. The respiratory rise began as ethylene production increased, reaching its maximum ≈30 to 40 hours after ethylene production had peaked. Green skin coloration and photochemical efficiency, as measured by chlorophyll fluorescence, declined simultaneously after the peak in ethylene biosynthesis. Natural ester biosynthesis began 40 to 50 hours after the peak in ethylene biosynthesis, reaching maximal levels 3 to 4 days later. While AAT expression was detected throughout, the maximum level of expression was detected at the onset of natural ester biosynthesis. The synthesis of unsaturated esters began 100 hours after the peak in ethylene and increased with time, suggesting the lipoxygenase pathway be a source of ester substrates late in ripening. Incorporation of exogenously supplied ester precursors (1-butanol, butyric acid, and 3-methyl-1-butanol) in the vapor phase into esters was maturity-dependent. The pattern of induced esters and expression data for AAT suggested that banana fruit have the capacity to synthesize esters over 100 hours before the onset of natural ester biosynthesis. We hypothesize the primary limiting factor in ester biosynthesis before natural production is precursor availability, but, as ester biosynthesis is engaged, the activity of alcohol acyl-CoA transferase the enzyme responsible for ester biosynthesis, exerts a major influence.

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Sven Verlinden, Silvanda M. Silva, Robert C. Herner, and Randolph M. Beaudry

The rate of respiration and the concentrations of sucrose, glucose, and fructose were measured along the length of intact asparagus (Asparagus officinalis cv. Jersey Giant) spears during storage at 0 °C. Carbon dioxide production by each of five sections along the spear was initially high but underwent a rapid and extensive decline within the first 24 hours after harvest with the rate of decline slowing thereafter. The respiration rate was highest at the tip (Section 1), decreasing as the distance from the tip increased (Sections 2 through 5 with Section 5 being more basal). Initially, the respiration rate of the tip was approximately four times that of the base, but after 23 days at 0 °C, the respiration rate of the tip was only twice that of the base. Sugar levels were measured in Sections 1 through 4. Sugar levels declined with time, but increased, unlike respiration, with distance from the tip. Sucrose underwent a rapid decline within the first 24 hours of storage in the tip and Sections 3 and 4. Sucrose depletion was most extensive in the tip, reaching more than 95% by Day 23. Glucose underwent the most rapid decline in Section 2. The relatively higher rate of glucose depletion in Section 2, the zone of rapid cell elongation, may have been to support a relatively higher rate of cell wall biosynthesis in this section. For the first day after harvest, sugar depletion far outstripped hexose equivalents respired as CO2. Afterward, however, the rate of respiration (as hexose equivalents) was similar to the rate of sugar depletion for all sections except the most basipetal, which lost carbohydrate faster than could be accounted for by respired CO2. The data suggest that hexoses were exported from more basipetal tissues to support the metabolic activity of more acropetal sections.

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Nigel H. Banks, Donald J. Cleland, Arthur C. Cameron, Randolph M. Beaudry, and Adel A. Kader

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Chris B. Watkins, Randolph M. Beaudry, Terence L. Robinson, and Alan N. Lakso

ReTain™, a commercial plant growth regulator containing aminoethoxyvinylglycine, an inhibitor of ethylene production, was applied 4 weeks before normal harvest to `Jonagold' trees and the effects on fruit maturity and quality at harvest, and quality after air and controlled atmosphere storage was investigated. When fruit were harvested from 3 to 6 weeks after treatment, fruit ripening was inhibited as indicated by lower internal ethylene concentrations, delayed starch hydrolysis, and lower levels of skin greasiness. A number of factors indicated that other aspects of fruit metabolism were affected by the compound. Treated fruit were softer than nontreated fruit at the first harvest, and the benefits of ReTain on firmness appeared only at the later harvests. Also, at each harvest date, average fruit weight of ReTain-treated fruit was lower than nontreated fruit. We have investigated the possibility the ReTain and/or the accompanying surfactant, Silwet, inhibited leaf photosynthesis, thereby leading to altered carbon metabolism. Trees were unsprayed, or sprayed with surfactant, and ReTain plus surfactant. No treatment effects on photosynthesis were detected. However, leaf photosynthesis rates were generally low and quite variable. Measurements of fruit diameter confirmed that the increase in fruit volume following treatment was ≈2% less on the ReTain plus surfactant-treated fruit than nontreated fruit. The increase in fruit volume for the Silwet treatment was ≈1.5% less than in untreated fruit. The data indicates a rapid change in fruit volume as fruit changed in color. Inhibition of ethylene by ReTain may be an important factor influencing fruit size.

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Nazir A. Mir, Erin Curell, Najma Khan, Melissa Whitaker, and Randolph M. Beaudry

Fruit of `Redchief Delicious' apple [Malus sylvestris (L) Mill. var. domestica (Borkh.) Mansf.] were harvested 1 week before the climacteric (harvest 1), at the onset of the climacteric (harvest 2), and 1 week after the onset of the climacteric (harvest 3). Fruit were stored at 0, 5, 10, 15, or 20 °C and were treated with 0.7 μL·L-1 1-MCP on a once-per-week, once-per-2-week, once-per-month, and once-per-year basis or were left nontreated. The initial 1-MCP treatment was at 20 °C and subsequent applications were at storage temperatures. The compound slowed softening at all temperatures relative to nontreated fruit, however as temperature decreased, the benefits of 1-MCP application became less pronounced. Effectiveness of 1-MCP declined slightly as harvest maturity increased. Efficacy of 1-MCP treatment increased with greater frequency of application at 5, 10, 15, and 20 °C, but not at 0 °C. Fruit stored without refrigeration (20 °C) for more than 100 days did not soften significantly when treated once per week with 1-MCP. However, decay was a significant problem for treated and nontreated fruit stored at temperatures >5 °C; 1-MCP application reduced, but did not prevent decay. Rate of decline in titratable acidity increased with storage temperature and 1-MCP had no significant effect on retarding the decline in acid content. Minimal (Fo) and maximal (Fm) chlorophyll fluorescence was altered markedly by 1-MCP application, but the ratio of (Fm-Fo)/Fm was only slightly affected. The most effective 1-MCP treatment frequency was once per week and, at all elevated temperatures (5, 10, 15, and 20 °C), slowed loss of firmness to a greater extent than refrigeration (0 °C) alone. Application of 1-MCP resulted in greater retention of firmness than controlled atmosphere (CA) with O2 and CO2 at 1.5 kPa and 3 kPa, respectively. Data suggest that 1-MCP application, has the potential to reduce reliance on refrigeration and CA storage for maintaining firmness of `Redchief Delicious' apple, especially for relatively short storage durations (<50 days) when fruit are harvested within a week of the ethylene climacteric. Chemical name used: 1-methylcyclopropene (1-MCP).

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Randolph M. Beaudry, Arthur C. Cameron, Ahmad Shirazi, and Diana L. Dostal-Lange

Highbush blueberry (Vaccinium corymbosum L. `Bluecrop') fruit sealed in low-density polyethylene packages were incubated at 0, 5, 10, 15, 20, or 25C until O2 and CO2 levels in the package reached a steady state. A range of steady-state O2 partial pressures (1 to 18 kPa) was created by placing a range of fruit weights within packages having a constant surface area and film thickness. The steady-state O2 partial pressure in packages containing the same weight of fruit decreased as temperature increased, indicating the respiratory rate rose more rapidly (i.e., had a greater sensitivity to temperature) than O2 transmission through the film. Steady-state O2 and CO2 partial pressures were used to calculate rates of O2 uptake. CO2 Production. and the respiratory quotient (RO). The effects of temperature and 02 partial pressure on O2 uptake and CO2 production and the RQ were characte∼zed. The steady-state O, partial pressure at which the fruit began to exhibit anaerobic CO2 production (the RQ breakpoint) increased with increasing temperature, which implies that blueberry fruit can be stored at lower O2 partial pressures when stored at lower temperatures.

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Arthur C. Cameron, Randolph M. Beaudry, Nigel H. Banks, and Mark V. Yelanich

A mathematical model was developed to characterize the interaction of fruit O2 uptake, steady-state O2 partial pressures in modified-atmosphere (MA) packages ([O2]pkg), and film permeability to O2 (Po 2) from previously published data for highbush blueberry (Vaccinium corymbosum L. `Bluecrop') fruit held between 0 and 25C. O2 uptake in nonlimiting O2 (Ro 2 max,T) and the [O2]pkg at which O2 uptake was half-maximal (K½ T) were both exponentially related to temperature. The activation energy of 02 uptake was less at lower [O2]pkg and temperature. The predicted activation energy for permeation of O2 through the film (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{E}_{\mathrm{a}}^{\mathrm{P_{\mathrm{o}_{2}}}}\) \end{document} kJ·mol-1) required to maintain close-to-optimum [O2]pkg across the range of temperatures between 0 and 25C was ≈ 60 kJ·mol-1. Packages in which diffusion was mediated through polypropylene or polyethylene would have values \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{E}_{\mathrm{a}}^{\mathrm{P_{\mathrm{o}_{2}}}}\) \end{document} of ≈ 50 and 40 kJ·mol-1, respectively, and would have correspondingly greater tendencies for [O2]pkg to decrease to excessively low levels with an increase in temperature. Packages that depend on pores for permeation would have an \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{E}_{\mathrm{a}}^{\mathrm{P_{\mathrm{o}_{2}}}}\) \end{document} of <5 kJ·mol-1. Our procedure predicted that, if allowed to attain steady-state conditions, packages with pores and optimized to 2 kPa O2 at 0C would become anaerobic with as little as a 5C increase in temperature. The results are discussed in relation to the risk of temperature abuse during handling and marketing of MA packaged fruit and strategies to avoid induction of anaerobiosis.

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Dennis W. Joles, Arthur C. Cameron, Ahmad Shirazi, Peter D. Petracek, and Randolph M. Beaudry

`Heritage' raspberries (Rubus idaeus L.) were sealed in low-density polyethylene packages and stored at 0, 10, and 20C during Fall 1990 and 1991 to study respiratory responses under modified atmospheres. A range of steady-state O2 and CO2 partial pressures were achieved by varying fruit weight in packages of a specific surface area and film thickness. Film permeability to O2 and CO2 was measured and combined with surface area and film thickness to estimate total package permeability. Rates of O2 uptake and CO2 production and respiratory quotient (RQ) were calculated using steady-state O2 and CO2 partial pressures, total package permeability, and fruit weight. The O2 uptake rate decreased with decreasing O2 partial pressure over the range of partial pressure studied. The Michaelis-Menten equation was used to model O2 uptake as a function of O2 partial pressure and temperature. The apparent Km(K½) remained constant (5.6 kPa O2 with temperature, while Q10 was estimated to be 1.9. RQ was modeled as a function of O2 partial pressure and temperature. Headspace ethanol increased at RQs >1.3 to 1.5. Based on RQ, ethanol production, and flavor, we recommend that raspberries be stored at O2 levels above 4 kPa at 0C, 6 kPa at 10C, and 8 kPa at 20C. Steady-state CO2 partial pressures of 3 to 17 kPa had little or no effect on O2 uptake or headspace ethanol partial pressures at 20C.

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Christopher B. Watkins, Mustafa Erkan, Jacqueline F. Nock, Kevin A. Iungerman, Randolph M. Beaudry, and Renae E. Moran

`Honeycrisp' is a new apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] cultivar that has been planted extensively in North America, but the storage disorders soggy breakdown and soft scald have resulted in major fruit losses. The effects of harvest date and storage temperature on fruit quality and susceptibility of fruit to these disorders have been investigated in Michigan, New York, and Maine. Internal ethylene concentrations were variable over a wide range of harvest dates, and a rapid increase in autocatalytic ethylene production was not always apparent. The starch pattern index, soluble solids content, titratable acidity and firmness also appear to have limited use as harvest indices. Development of soggy breakdown and soft scald is associated with later harvest dates and storage of fruit at temperatures of 0 to 0.5 °C compared with higher storage temperatures. It is recommended that `Honeycrisp' be stored at 3 °C, although storage disorders still can occur at this temperature if fruit are harvested late. In addition, greasiness development may be worse at higher storage temperatures.

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Cindy B.S. Tong, David S. Bedford, James J. Luby, Faye M. Propsom, Randolph M. Beaudry, James P. Mattheis, Christopher B. Watkins, and Sarah A. Weis

The effects of growing and storage locations and storage temperature on soft scald incidence of `Honeycrisp' apples were examined. In 1999 and 2000, fruits were produced at five different locations, harvested at two different times, and stored at two or five different storage locations. In 1999, fruits were stored at 0 or 2 °C. Soft scald was only observed in fruits from one growing location and primarily at 0 °C. More soft scald was observed from the second harvest than from the first. Scalded fruits were preclimacteric as determined by ethylene production rate, whereas fruits from the other locations were postclimacteric. In 2000, fruits from four of the growing locations developed soft scald, and soft scald incidence was not related to ethylene production rate. Scalded fruits had higher concentrations of phosphorus, boron, and magnesium, and lower concentrations of manganese than unaffected fruit. Development of soft scald was not related to fruit ethylene production rates, was dependent on growing location, increased with later harvest, and may be related to fruit elemental content.