Steven A. Sargent

Modified atmosphere packaging for mixed loads of horticultural commodities exposed to two postharvest temperatures

A procedure to maintain desired levels of O2 and CO2 inside packages that are exposed to different surrounding temperatures was designed and tested. This procedure included the design of packages for a high temperature, ambient atmosphere conditions simulating retail display conditions and the use of a controlled atmosphere (CA) environment surrounding the packages at a lower temperature simulating storage or transport conditions. To test the concept, strawberries and snap beans were held at 7°C for 4 days and 19°C for 2 days to simulate mixed storage:transport and retail display at these respective temperatures. The strawberries were stored in jars fitted with a short tube to modify the interior atmosphere; snap beans were stored in commercially available, semipermeable plastic bags. Both package types were placed in a CA of 14.8% O2 plus 8.3% CO2 at 7°C followed by storage in air at 19°C. Under these conditions, it was possible to maintain atmospheres that were close to the desired atmospheres for the products at both temperatures.

Oxidation-reduction potential of chlorine solutions and their toxicity to Erwinia carotovora subsp. carotovora and Geotrichum candidum

The toxicity of chlorine solutions to cells of Erwinia carotovora subsp. carotovora and conidia of Geotrichum candidum suspended in water at pH 6.0, 7.0, or 8.0 was correlated with the free chlorine concentration and oxidation-reduction potential of the solutions. The oxidation-reduction potential was directly correlated with the Log 10 of the chlorine concentration at each pH. Cells of E. c. carotovora were 50 times more sensitive to chlorine than were conidia of G, candidum, with populations of 1 × 10 7 cfu/ml and 1 × 10 7 conidia per milliliter, respectively, Populations of E. c, carotovora were reduced below detectable levels (< 10 2 cfu/ml) by approximately 0,5, 0,5, or 0,75 mg of free chlorine per liter at pH 6.0, 7.0, or 8.0, respectively. In contrast, with conidia of G. candidum, 25, 25, and greater than 30 mg/L, respectively, were required to produce a similar level of efficacy. With both organisms, population reductions were associated with higher initial oxidation-reduction potentials at pH 6.0 than at pH 8.0

Chlorine Concentration and the Inoculation of Tomato Fruit in Packinghouse Dump Tanks

Chlorine concentrations (pH 6 to 7 and 22 to 27°C) that killed arthrospores (spores) of Geotrichum candidum or sporangioles (spores) of Rhizopus stolonifer, causal agents of sour rot and Rhizopus rot, respectively, in moving water within 30 to 45 s did not prevent these pathogens from inoculating wounded tomatoes (Lycopersicon esculentum) in a water flume containing chlorine and spores. Free chlorine concentrations of 20 or 25 mg/liter were lethal to spores of G. candidum within 30 s in most in vitro tests, whereas spores of R. stolonifer were slightly less sensitive. Wounded tomatoes placed in a flume with free chlorine at 30 mg/liter and then exposed to spores for 1 min developed about 50% less decay incidence during storage at 24°C for 6 days than did fruit exposed to spores and water alone. In the absence of chlorine, incidence averaged 57% (range, 15 to 95%) for R. stolonifer and 38% (range, 17 to 58%) for G. candidum. Sporadic sour rot lesions were observed among fruit that had been treated with free chlorine at 75 mg/liter, whereas chlorine at up to 180 mg/liter failed to completely protect fruit from Rhizopus rot. A water-soluble dye rapidly penetrated wounds on tomato fruit. The dye framed the outlines of cells at the wound surface and appeared to penetrate into a few intercel-lular spaces. Application of 1% sodium hypochlorite decolorized the dye on the wound surface, whereas deposits located below the wound surface remained blue. Thus, spores suspended in moving water can escape the action of chlorine if carried into intercellular spaces by diffusion or by capillary movement of cell sap and water.

Postharvest Decay Risk Associated with Hydrocooling Tomatoes

Tomatoes (breaker stage) hydrocooled with a cell suspension of Erwinia carotovora subsp. carotovora containing 50 to 200 mg of free chlorine per liter (ppm) (10°C, pH 7) remained decay free during a 10-day storage at 20°C. Sporadic disease appeared during storage of tomatoes similarly cooled with chlorinated water containing spores of Rhizopus stolonifer. In contrast, when chlorine was omitted from the pathogen suspensions, 50 to 100% of the fruit became diseased. A laboratory-scale shower hydrocooler reduced fruit temperatures from 35 to 15°C within 13.3 min, whereas a flume cooler produced the same temperature reduction in 10.5 min. In both systems, tomatoes increased in weight during cooling, evidence for water uptake. Larger weight increases occurred among tomatoes cooled in the shower than in the flume. An upward instead of downward orientation of stem scars under the shower streams led to significantly larger weight increases, presumably because pores in the stem scar were continuously flooded with water. Tomatoes intermittently submerged in cold water (10 2-min immersions followed by 30-s pauses) absorbed significantly less water than those continuously submerged for 20 min. Hydrocooling appears to be a viable method for rapid cooling of tomatoes. Technical refinements in the hydrocooling process that prevent continuous coverage of fruit surfaces by water should reduce water uptake and the associated risk of pathogen internalization. Maintenance of free chlorine at up to 200 ppm in the cooling water and prevention of direct water pressure on fruit should minimize decay risks. No evidence of phytotoxicity was observed among fruit infiltrated with 200 ppm of chlorine. These tomatoes ripened similarly to those that were not cooled or were cooled in tap water.

An assessment of the decay hazard associated with hydrocooling strawberries

The decay hazard associated with hydrocooling strawberries was related to whether they became inoculated with postharvest pathogens during the procedure. Storage of hydrocooled berries at warmer temperatures or for longer periods than recommended allowed inoculation to be expressed into disease. Cooling strawberries by immersion hydrocooling did not consistently lead to increased postharvest decays when compared with conventional forced-air cooling in two separate trials. No differences in decay incidence were found in berries that were hydrocooled versus forced-air cooled and then stored 7 days at 1°C plus 1 day at 20°C. With a 15-day storage regime (14 days at ≤7°C plus 1 day at 20°C), hydrocooled fruit developed less decay than forced-air-cooled fruit in one trial but more decay in a second. Wrapping baskets of cooled berries with plastic film promoted disease development and slowed the moisture loss from both hydrocooled and forced-air-cooled berries. The wrap did not promote disease more when applied to wet, hydrocooled berries as compared with dry, forced-air-cooled berries. Residual moisture left on the berries by the hydrocool treatment did not predispose the fruit to postharvest decays. In contrast, wounds and abrasions on hydrocooled fruit were temporarily water soaked and berries typically increased in weight as they were hydrocooled. Berries cooled in water containing spores of Botrytis cinerea or Rhizopus stolonifer developed nearly 100% decay incidence during a storage regime that favored specific development of gray mold (11 days at 7°C) or Rhizopus rot (2 days at 24°C). Chlorinating the hydrocooler water (120 mg of free chlorine per liter at pH 6.5) before adding the berries and spores reduced the incidence of gray mold to 43%; in contrast, berries hydrocooled in clean water developed 61% gray mold. Chlorination of the clean water led to significant reductions in the incidence of gray mold (44%) but did not affect the incidence of Rhizopus rot. The hydrocool method for cooling strawberries with the addition of proper chlorination has promise as a rapid method for cooling and cleaning berries and reducing gray mold inoculum on berry surfaces.

Ethylene-induced overproduction of reactive oxygen species is responsible for the development of watersoaking in immature cucumber fruit.

Watersoaking is an ethylene-induced disorder observed in some members of the Cucurbitaceae including cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus Thunb. Matsum and Nakai), and tropical pumpkin (Cucurbita moschata Duch.). Previous studies have found that immature beit-alpha cucumber (cv. Manar) exhibit watersoaking after 6d of continuous exposure to 10 μLL(-1) ethylene in air (21 kPa O(2)). The present study was designed to investigate the early dynamics of ethylene responses in immature cucumber fruit in order to provide insight into the watersoaking triggering mechanism. Changes in respiration, epidermal color, firmness, reactive oxygen species (ROS) production and electrolyte leakage were evaluated as a function of time under different ethylene concentrations and exposure duration. Ethylene concentrations exceeding 10 μLL(-1) did not accelerate changes in any of the evaluated responses. The first detectable change was a significant rise in respiration on day 2, followed by a significant rise in ROS on day 4, and significant degreening, mesocap softening, and increased electrolyte leakage on day 6; the latter responses coincident with incipient watersoaking. Varying the duration of exposure to ethylene indicated that the critical exposure time is between 2 and 4d. Notably, all deleterious responses to ethylene were suppressed under a hypoxic atmosphere. A model is proposed in which ethylene induces a sharp increase in respiration with a concomitant sharp rise in ROS, which the immature fruit is incapable of quenching. The resulting production of excess ROS leads to discoloration and membrane deterioration, leading to the release of cytoplasmic content, rapid softening, and the visual symptom of watersoaking.

Tubes for modified atmosphere packaging of fresh fruits and vegetables: Effective permeability measurement

Tubes can serve as mediators of gas exchange between the atmosphere inside an impermeable modified package and the surrounding atmosphere. Gas permeabilities through different size tubes (diameter: 0.0065, 0.010, 0.012 and 0.016 m; length: 0.005, 0.010, 0.015, 0.020, 0.022, 0.030, 0.040 m) were measured at 1.5°C, 7°C, and 19°C. It was found that gas permeabilities through tubes were not significantly affected by temperature in the range tested; however tube diameter and length did affect gas permeability. An increase in tube diameter and/or decrease in tube length caused an increase in gas permeability. A regression model relating permeability to tube diameter and length was developed. Oxygen permeability was always greater than carbon dioxide permeability for the same tube dimensions, and permeability ratios (K*B /K*A ) of tubes were found to be between 0.72 and 0.98.

Instrumented Sphere Impact Analyses of Tomato and Bell Pepper Packing Lines

Transfer points with potential to cause mechanical injury were identified in 11 tomato packing lines (5 packing green tomatoes, 5 packing tomatoes showing red color, 1 repacker); 3 bell pepper packing lines; and 2 mobile field pack units for peppers. Average maximum impact levels for the lines packing tomatoes with red color were higher than those packing green tomatoes. Field pack units for peppers had significantly fewer numbers of impacts than the pepper packing lines. Modifications to some transfer points resulted in over 50% reduction in impact levels.

Effect of High Tunnels on the Growth, Yields, and Soluble Solids of Strawberry Cultivars in Florida

Two studies were conducted to compare the effects of high tunnel and open-field production on the growth, fruit earliness, yield, and soluble solid content of Florida strawberry cultivars. Three strawberry cultivars and two production systems were tested inside high tunnels and in open fields. The cultivars were ‘Strawberry Festival’, ‘Winter Dawn’, and ‘Florida Elyana’. Production systems and cultivars significantly affected strawberry early and total yields, but the interaction between both factors was not significant. Early yields increased by up to 54% inside high tunnels in comparison with those from open fields. Strawberry total marketable yields maximized inside high tunnels in comparison with open fields, with up to 63% fruit weight increments. Fruit yields after freezing events and soluble solid contents were also increased inside high tunnels. Using high tunnels in Florida for strawberry production might benefit growers by improving earliness and providing a competitive edge in the market, reducing sprinkler irrigation use for freeze protection, hence lowering fruit damage and fuel or electricity costs, and the incidence of foliar and fruit diseases.

Strawberry fruit resistance to simulated handling

ABSTRACT: Harvest operations are currently the main source of mechanical injury of strawberry( Fragaria x ananassa Duch. ). Experiments were designed to simulate conditions encountered duringcommercial handling. Individual fruits were subjected to impact or compression forces with similarenergy to determine the sensitivity to mechanical injury. Bruise volume was used as the measurementof injury. Bruise severity increased as a function of impact energy for both impact types. However,dropped fruits had larger bruise volume than fruits submitted to pendulum impactor at the sameenergy level. Doubling the impact energy (0.040 to 0.083 J) increased bruise volume by 7 times (13 to91 mm 3 ). Fruits dropped from 380 mm (0.075 J) showed 71% greater bruise volume than those droppedfrom either 130 mm (0.025 J) or 200 mm (0.040 J). Compressed fruits showed higher bruise volume thanother tests. Some cultivars are more susceptible to compression forces than others. ‘Sweet Charlie’berries showed bruise volume 40% higher than the others cultivars when subjected to compression.Fruits subjected to impact showed bruise volume lower than the compressed fruits, indicating thepossibility to be handled and graded in a packing line.Key words: