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  • Author or Editor: Kenneth A. Corey x
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Mathematical procedures for predicting steady-state O2 concentrations for a range of packaging conditions for modified-atmosphere packages (MAP) of `Heinz 1370' tomato (Lycopersicon esculentum) were developed and tested. The relationship between O2 consumption rate and O2 concentration was determined using O2 depletion data collected by enclosing tomatoes in jars and sampling head space O2 concentration over time. The fitted function was then used in conjunction with the input variables film permeability to O2 (PO2), film surface area (A), and fruit weight in packages (Wp) to develop an equation to predict steady-state O2 concentrations for different packaging ratios (A/Wp) and film permeabilities. Prediction curves showing steady-state O2 concentration for packaging ratios in the range of 1 to 12 closely resembled best-fit curves of experimental data. Increasing temperature from 20 to 28C had little effect on in-package O2 concentration, but decreasing temperature from 28 to 10C led to higher in-package O2 concentrations. The predictive equation developed can be used to select appropriate films and optimize packaging ratios to achieve desired steady-state O2 concentrations for MAP of tomatoes.

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It frequently takes days or weeks to determine if desired steady state concentrations of gases are reached in modified atmosphere packages of produce when atmospheres are modified by commodity respiration. We present a rapid method for testing packaging films and designs with active modification of atmospheres by vacuum and N2 infusion. Reduction of O2 concentration in produce packages and commodity tissues was completed within minutes by using several cycles of vacuum and N2 infusion treatments. Produce packages were placed in a desiccator and subjected to repeated partial vacuums, each followed by infusion of N2 to one atmosphere. Resulting O2 concentrations in packages (polyethylene + ethyl-vinyl acetate additive) were dependent on the extent of vacuum and the number of evacuations. Within packages of tomatoes, O2 concentrations of 8.3% ± 0.5% and 5.0% ± 1.0% were measured following two evacuations at 460 and 360 mm Hg, respectively. Three evacuations of cabbage and muskmelon packages at 460 mm Hg resulted in O2 concentrations of 5.1% ± 1.4% and 5.0% ± 1.4%, respectively. Maintenance or deviation from actively established atmospheres by the film was determined within hours.

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Abstract

Ripening of ‘Charleston Gray’ watermelon fruits was accompanied by changes in the appearance and quantity of surface waxes. The structure of surface wax platelets observed with a scanning electron microscope changed from an intricate porous appearance for unripe fruits to a smoother, less porous appearance for optimally ripe and overripe fruits. Structural changes in waxes as fruit matured from the unripe to overripe stages were accompanied by a 71% increase in the quantity of epicuticular waxes. These observations suggest the possibility of monitoring the ripeness of watermelon fruit through changes that occur in the appearance and structure of surface waxes.

Open Access

Abstract

Differences in aperture area and frequency of stomata on fruits of two muskmelon (Cucumis melo L.) genotypes were determined by computerized image analysis of photomicrographs obtained by microrelief techniques. Acetate impressions of surface cellular features on polar and equatorial regions of the fruit were viewed by phase contrast microscopy, and photomicrographs of random fields of stomata were made. A minicomputer-based image processor scanned each photomicrograph and digitized the image of individual stomata. The image was displayed on a monitor and a digitizing tablet was used to mark end points on the axes of an ellipse circumscribing the effective aperture. A FORTRAN image processing system calculated the area of each ellipse. Resulting data showed a significantly lower stomatal aperture area and stomatal frequency on the surface of fruits of the netted genotype.

Open Access

Reduced atmospheric pressures may be used to minimize mass and engineering requirements for plant growth habitats used in some extraterrestrial applications. A chamber with high vacuum capability and thermal control at Kennedy Space Center was used to measure water loss of lettuce plants at reduced atmospheric pressures. A test stand with three, high-pressure sodium vapor lamps was used to determine short-term plant responses to reduced pressure. Initial experiments with lettuce showed that a pressure of 10 kPa (≈0.1 atm) resulted in a 6.1-fold increase in the rate of water loss compared to water loss at ambient pressure. However, due to low relative humidity, plants wilted after 30 minutes exposure to 10 kPa. A follow-up experiment in which relative humidity was controlled between 70% and 85%, demonstrated that water loss was directly proportional to the vapor pressure gradient, regardless of atmospheric pressure in the pressure range of 10 to 101 kPa. However, the response was curvilinear, suggesting effects on the pathway resistance. Results indicate that plant growth at atmospheric pressures of 5 to 10 kPa should be achievable. Further work will necessitate better relative humidity control and carbon dioxide control in order to separate vapor pressure deficit effects from diffusion effects.

Free access

Abstract

Three genotypes (‘Heinz 1350’, neglecta-1, yellow-green-5) of tomato (Lycopersicon esculentum Mill.) were grown during winter under natural light or with natural light supplemented with light from high-pressure sodium vapor (HPS) lamps (200-400 μmol·s-1·m-2). The plants were grown in sand culture with NO- 3 or NH+ 4 nutrition. Symptoms resembling Ca, Mg, K, and P deficiencies developed on the foliage of plants exposed to radiation from HPS lamps. Clustering of short branches in the lateral and terminal growing regions (yg-5) and epinasty (‘Heinz 1350’ and neg-1) developed on the shoots receiving HPS irradiation. Ethylene evolution by the three genotypes was enhanced by the supplemental lighting and NH+ 4 nutrition. Concentrations of Ca, Mg, K, and P in the shoots were lower in plants receiving HPS irradiation than in plants grown under natural light. Dry weights of shoots were increased by supplemental lighting relative to the weights of the plants receiving only natural light. Total accumulation of Ca, Mg, K, and P was not suppressed by HPS lighting, indicating that the phytotoxic effects of the lamps was not due to their effects on total nutrient accumulation.

Open Access

Abstract

Parthenocarpic cucumber (Cucumis sativus L. ‘La Reine’) plants were grown in the greenhouse in containers filled with equal parts by volume of peatmoss and vermiculite blended with 0%, 25%, or 50% by volume compost made from ferric-chloride-precipitated, lime-stabilized, digested sewage sludge composted with wood-chips and amended with various rates of sulfur. The Cd concentration of leaf and fruit samples from plants grown in media amended with 25% or 50% compost and S at 0, 10, 20, or 40 g·liter–1 was unaffected by changes in pH from 7.2 to 3.4. However, Zn concentration in fruit samples from plants grown in media amended with 25% compost and S at 40 g·liter–1 increased relative to other rates of S, whereas Zn concentration of leaf tissue was unaffected by rate of S application. Yield of fruit was not significantly affected by any of the treatments. Cucumber plants can be grown successfully in media amended with as much as 50% composted sewage sludge low in heavy metal content and over a wide range of pH values without the accumulation of fruit Cd levels hazardous to human health.

Open Access

Abstract

Field experiments were conducted on a Norfolk loamy sand (fine-loamy, siliceous, thermic Typic Paleudult) from 1983 through 1985 to determine the effects of tillage method, cover crop, and N fertilization on inorganic soil N and yield, yield components, and N content of snap bean (Phaseolus vulgaris L.). Hairy vetch (Vicia villosa Roth), hairy vetch plus wheat (Triticum aestivum L.), Austrian winter pea (Pisum sativum ssp. arvense L. Poir), Austrian winter pea plus wheat, wheat, crimson clover (Trifolium incarnatum L.) and no cover were the cover crop treatments. Inorganic N concentrations generally were greater in soil with cover crop treatments containing legumes than in soil with no cover and wheat treatments. The use of Austrian winter pea, hairy vetch, and crimson clover as cover crops without supplemental N resulted in snap bean yields comparable to those obtained when 90 kg·ha−1 additional N was supplied. Supplemental N decreased the amount of dry matter partitioned into pods. Inorganic N profiles in the soil indicated that conventional tillage (CT) practices resulted in greater mineralization of N fixed by the legume cover crops than no-tillage (NT) practices. However, snap bean yields for NT were comparable to or greater than those obtained with CT, suggesting that N released from legume residues provided sufficient supplemental N for optimum growth and yield.

Open Access