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R.B.H. Wills and M.A. Warton

A systematic study was conducted on the ability of potassium permanganate absorbent to remove low levels of ethylene from the atmosphere. Absorption of potassium permanganate onto alumina beads by dipping in a saturated solution was maximal at 2 g/100 g after 2 hours at 20 °C and 4 g/100 g after 1 hour at 65 °C. Commercial alumina-based absorbents were found to contain potassium permanganate at 2.7 to 6.0 g/100 g suggesting many are prepared at elevated temperature. Trials in a closed system at 20 °C and 60% to 70% RH with alumina beads containing potassium permanganate at 4 g/100 g showed a logarithmic decrease in ethylene concentration with 90% of the ethylene removed after 2.5 to 3.0 hours. Relative humidity (RH) had a marked inverse effect on ethylene absorption with reactivity at 100% RH calculated to be 15% of that at 0% RH. Performance of potassium permanganate where ethylene was continually generated by a continuous flow of ethylene at 14 μL·h-1 through the container showed a steady state was attained within 1 hour and maintained for 24 hours. Ethylene removal increased linearly with bead weight and ranged from 30% with 1 g to 90% with 50 g. Examination over 20 days showed a continuing decrease in rate of ethylene removal which after 14 days had declined to 10% of incoming ethylene although 44% of the original level of potassium permanganate still remained in the beads. Calculations based on known endogenous ethylene production rates suggest that at 20 °C and 90% RH, use of a potassium permanganate-alumina absorbent would be beneficial with produce having a low level of ethylene generation. Suitability for larger packages of produce generating higher ethylene levels is questionable as >1 kg of absorbent may be required.

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L. Soegiarto and R.B.H. Wills

Broccoli (Brassica oleracea), green bean (Phaseolus vulgaris), and bok choy (Brassica chinensis) were fumigated with nitric oxide (NO) gas in air or in nitrogen for 2 hours at 20

°C (68.0 °F), then stored at 20 °C in humidified air containing 0.1 μL.L-1 (ppm) ethylene. The postharvest life of all vegetables was extended by NO although the concentration of NO required and the magnitude of the extension varied between produce ranging from 14% for green bean to more than 50% for broccoli. NO uptake by produce from air was not significantly different than from nitrogen at the lower effective NO concentrations, but NO uptake was less from air at the highest concentration used for broccoli. Application of NO in an air atmosphere is considered a feasible, more convenient treatment regime for horticultural produce than use of a nitrogen atmosphere.

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D. Badiyan, R.B.H. Wills, and M.C. Bowyer

Snapdragon (Antirrhinum majus L. `Chitchat'), delphinium (Delphinium ajacis L. `Bellisimo'), chrysanthemum (Dendranthema grandiflora RAM. `Regan'), tulip (Tulipa hybrid `Golden Brush'), gerbera (Gerbera jamesonii H. Bolus `Manovale'), oriental lily (Lilium asiaticum L. `Specisiom Simplon'), rose (Rosa hybrid L. `Carnavale') and iris (Iris hollandica Tub. `Blue Magic') cut flower stems were placed at 20 °C in water containing the NO donor compound 2,2'-(hydroxynitrosohydrazino)-bisethanamine (DETA/NO) at 10 and 100 mg·L-1 and after 24 h, transferred to humidified air containing 0.1 μL·L-1 ethylene. Compared with flowers kept in water, the vase life of all eight flowers was extended by DETA/NO with an average extension of about 60% with the range being about 200% for gerbera to 10% for chrysanthemum. DETA/NO appears to have widespread applicability to cut flowers and offers a simple technology to extend vase life.

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R.B.H. Wills, M.A. Warton, and J.K. Kim

Potato tubers (Solanum tuberosum cv. Sebago) were stored at 20 °C in air containing ethylene at <0.005, 0.01, 0.1, 1.0, or 10 μL·L-1 and the level of sprouting was measured over 35 days. The time for tubers to develop an average of one sprout per tuber was found to linearly increase as the log10 ethylene concentration decreased with the effect present over the whole range of concentration. After 35 days of storage, the number of sprouts/tuber was inversely related to the ethylene concentration, but the weight of sprouts was only lower for tubers held in <0.005 μL·L-1 ethylene. The more numerous sprouts on tubers held in 10 μL·L-1 ethylene were short and thick, while the less numerous sprouts on tubers in 0.01-1.0 μL·L-1 were long, thin, and branched, and resulted in no significant difference in total sprout weight between these concentrations. Reducing the concentration of ethylene in the atmosphere around stored potatoes thus reduced sprouting, but levels <0.01 μL·L-1 are required to minimize both sprout emergence and sprout growth.

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V.V.V. Ku, R.B.H. Wills, and S. Ben-Yehoshua

Strawberry (Fragaria ×ananassa Duch.) fruit were fumigated for 2 hours at 20 °C with 1-mcp at concentrations from 5 to 500 nL·L-1, then held at 20 and 5 °C in air containing 0.1 μL·L-1 ethylene. Fumigation with 1-mcp at 5 to 15 nL·L-1 extended the postharvest life by ≈35% at 20 °C and 150% at 5 °C, but at higher 1-mcp concentrations there was an accelerated loss of quality with a 30% to 60% decrease in postharvest life at 500 nL·L-1 at both 20 and 5 °C. Chemical name used: 1-methylcyclopropene (1-mcp).