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  • Author or Editor: Randolph M. Beaudry x
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The application of low oxygen through modified atmosphere packaging (MAP) is a technique used successfully to preserve the visual quality of lettuce and some other commodities. The expansion of use of low O2 via MAP to preserve quality of most commodities is limited by technical difficulties achieving target O2 concentrations, adverse physiological responses to low O2, and lack of beneficial responses to low O2. Low O2 often is not used simply because the physiological responses governed by the gas are not limiting quality maintenance. For instance, shelf life may be governed by decay susceptibility, which is largely unaffected by low O2 and may actually be exacerbated by the conditions encountered in hermetically sealed packages. Physiological processes influenced by low O2 and limit storability are discussed. The interdependence of O2 concentration, O2 uptake by the product, and temperature are discussed relative to requirements for packaging films.

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A theoretical model was developed that predicts how volatiles synthesized by fruit accumulate in the fruit interior and the fruit cuticle. Model inputs include temperature, rates of volatile synthesis, solubility of the volatile in the cuticular material, and the permeability of the volatile through the cuticle. The model indicated that the accumulation of volatiles was highly temperature-dependent and dependent upon the nature of the interaction between the volatile and the cuticle. For volatiles whose cuticular permeability declined rapidly with temperature, the concentration in the fruit and fruit cuticle tended to increase with decreasing temperature. This accumulation of volatiles in the fruit and fruit cuticle with decreasing temperature was enhanced by a decrease in the heat of solution (i.e., temperature sensitivity of solubility) and diminished by an increase in the Q10 Of the rate of volatile synthesis (i.e., the temperature sensitivity of the rate of synthesis). The model suggests that storage temperature can influence volatile retention and, hence, the volatile profile.

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Blueberry fruit were sealed in 0.00254 cm (1 mil) thick, 200 cm2 low density polyethylene pouches, which, in turn, were sealed in containers continually purged with gas mixtures containing 0, 20, 40 or 60 kPa CO2 and held at 15C. Sampling the gas composition of the enclosed package permitted accurate determination of O2 uptake, CO2 production and the respiratory quotient (RQ) despite the high background CO2 levels. O2 uptake was minimally affected by the CO2 treatments. CO2 production, however, increased at CO2 partial pressures over 20 kPa, resulting in an elevated RQ at 40 and 60 kPa CO2. Raising the CO2 partial pressure caused the fruit to become more sensitive to lowered O2, raising the O2 partial pressure associated with the RQ breakpoint.

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The reasons for knowing the maturity of fruit center around controlling fruit quality after harvest. Farmers are usually concerned with trying to determine harvest date to fit their labor, storage, and marketing needs, whereas research scientists are typically trying to account for the effects of maturity as a variable in experiments. Specific goals for farmer and researcher will, in part, govern what maturity indices are used and what values are acceptable. Restrictions in time and equipment will also affect choice of maturity assessment methods. In some instances, internal or external characteristics might be more important. Because changes in a number of characteristics comprise ripening, there is no single criteria or method that can be termed “best.” However, for each situation, an optimal choice of criteria or method may exist. The logic and information necessary to reach those optimal choices, from the perspective of the researcher and the commercial horticulture operation, is presented and contrasted.

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We hypothesized that the blocking of O2 influx and CO2 efflux in banana (Musa acuminata) by sealing nearly 100% of the pores over a fraction of the surface would generate a modified internal atmosphere in a manner similar to fruit coatings that cover 100% of the banana surface but only block a fraction of the pores. This hypothesis was based on the observation made by previous workers that the flesh of mature green bananas has insignificant resistance to O2 diffusion relative to the resistance imposed by the skin of the fruit. We modified the O2 diffusion pathway in bananas by covering, beginning at one end, ¼, ½, ¾, and ⅞ of the fruit surface with paraffin, which sealed essentially 100% of the surface where it was applied. Large end-to-end O2 and CO2 gradients developed within coated fruit, relative to the uncoated control, suggesting that the diffusive resistance in the pulp was not insignificant. Since the large gradients of O2 generated caused uneven ripening, using fractional coatings may help analyze gas exchange properties, but it is not suitable for commercially controlling ripening of bananas.

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Abstract

Flux of ethylene from adaxial applications of Ethrel and Silaid to amphi- and hemistomatous leaves was examined. Following application of Ethrel to amphistomatous leaves in the dark (i.e., closed stomata) or hemistomatous leaves in the light, steady-state ethylene evolution was almost entirely adaxial. When stomata of amphistomatous leaves were fully open, abaxial ethylene flux for Ethrel was about 45% of the total ethylene evolved. Abaxial ethylene flux could then be dramatically reduced by stomatal closure induced by low light levels. Steady-state abaxial flux of ethylene from Silaid on amphistomatous leaves in the dark or hemistomatous leaves in the light was usually equal to or greater than adaxial ethylene flux. When stomata of amphistomatous leaves were fully open, flux of ethylene from Silaid was invariably equal from both leaf surfaces. Flux of Silaid- or Ethrel-derived ethylene from one leaf surface was reduced by increasing air velocity on the opposite side of the leaf, but only on amphistomatous leaves following light-induced stomatal opening. For Ethrel, the effect of air velocity was greater when the side of the leaf to which Ethrel had been applied was exposed to the increased air flow. No similar effect was found for Silaid. Closure of stomata on amphistomatous leaves and use of hemistomatous leaf material prevented any air velocity effect. Data indicate little to no entry of Ethrel or Ethrel-derived ethylene into the side of a leaf that lacks stomata or whose stomata are tightly closed. Significant movement of Silaid into leaf tissues probably occurs regardless of stomatal status, resulting in considerable release of ethylene within the leaf. Chemical names used: (2-chloroethyl)phosphonic acid (Ethrel); (2-chloroethyl) methylbis(phenylmethoxy)silane (Silaid).

Open Access

Abstract

Ethylene-induced abscission of pepper (Capsicum frutescens L. cv. Hungarian Hot Yellow Wax) flower buds, leaves, and fruit depended on ethylene source (i.e. ethylene gas from a compressed gas source vs. ethylene released from Silaid) and concentration. In response to ethylene from either source, flower buds and small fruit (< 10 mm long) abscised most readily and fully expanded leaves least readily. Concentrations of Silaid that induced fruit abscission comparable to a given concentration of ethylene gas induced significantly greater leaf abscission than ethylene gas. Application of Silaid at dusk resulted in a small, but significant, increase in abscission relative to early morning application. Progressive increases in temperature between 18° and 32°C enhanced fruit and leaf abscission in response to ethylene gas. Abscission mediated by ethylene gas was not affected by light intensities between 120 and 300 µmol·m–2·s–1 PAR. Chemical name used: (2-chloroethyl)methylbis(phenyImethoxy)silane (Silaid, CGA-15281).

Open Access

Volatile production is known to change with stages of plant organ development. Research has primarily focused on ripening-related volatiles; however, the potential exists to use volatiles as markers of organ damage and senescence. We have employed gas chromatography/mass spectrometry to establish stages of senescence based on volatile profiles of whole and lightly processed broccoli and carrot. An air-tight chopping apparatus was used as a flow-through chamber system and the exit gas stream analyzed for each commodity with and without tissue disruption. For carrot, isoprenoid pathway volatiles, such as 3-carene, caryophellene, α-caryophellene, and β-pinene, increase with damage and tissue senescence. Similar trends were obtained for broccoli with volatiles characteristic of β-oxidation and shikimic acid pathways. Time and condition-related volatile profile changes will be presented for carrot, broccoli, and strawberry.

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O2 and CO2 permeabilities were determined for experimental polyethylene polymers (Dow Plastics, Freeport, Texas) in relation to low-density polyethylene (LDPE) films for the packaging of horticultural commodities. A stainless steel flow-through permeability cell was used to determine O2 and CO2 permeabilities at 0, 5, 10, 15, 20 and 25C for the polymers. Data were fitted to the Arrhenius' relationship and the Arrhenius' constant and energy of activation were determined. In addition, flow-through containers of sealed cherry tomatoes at room temperature were used to determine ethylene permeability of the polymers. The new polymers were several times more permeable than LDPE to O2, CO2, and ethylene. The results were incorporated into a model for predicting O2 concentrations over a temperature range for sliced apple fruit. The greater permeability of the new polymers will improve control of O2 and CO2 in modified atmosphere packages and enhance flexibility of package design.

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A simple packaging system was developed to simultaneously measure volatile production by plant organs and the permeability of the packaging film to those volatiles. In this system, apple (Malus domestica Borkk cv Golden Delicious) was packaged in low-density polyethylene (LDPE) bag and placed into a glass jar with a low air flow. The package and jar head spaces were sampled for aroma volatile analysis by gas chromatograph. Analysis was by gas chromatography/mass spectrometry. This system allowed at least 10 volatile compounds and their permeabilities to be measured. This system permits volatile production to be measured for products in the package so the product need not be removed from its storage environment. This may be a useful method for determining the dynamic relationship between flavor volatile synthesis and package atmosphere for packaged produce.

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