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.

Mature, unripe mango, peach, custard apple, kiwifruit and tomato were stored at 20˚C in air containing ethylene at <0.005, 0.01, 0.1 1.0 and 10 L/L. The time to ripen of all the climacteric fruits increased linearly with logarithmic decrease in ethylene concentration over the whole concentration range examined. Similar observations were also obtained with kiwifruit and custard apple held at 0 and 14˚C, respectively. However, the sensitivity of fruits to ethylene varied with banana and kiwifruit > custard apple and mango > tomato, avocado and peach. Since the ethylene level around horticultural produce during marketing is always >0.005 L/L, the time climacteric fruit can be held in an unripe condition is currently less than optimal but intervention to limit ethylene action would appear to be only warranted for the most sensitive fruits.

This study examined the effect of fumigation of iceberg lettuce with 1-methylcyclopropene (1-MCP) at 0.1-1 ml l À1 for 1-5 h on the storage life at 5°C in air containing 0.1 ml l À1 ethylene. 1-MCP extended the storage life of shredded lettuce at all concentrations, with the optimal treatment being fumigation with 0.1 ml l À1 1-MCP for 1 h at 5°C, which resulted in an extension in storage life of about 50% over untreated lettuce. Application of this treatment to whole lettuce heads resulted in a 100% increase in storage life. 1-MCP thus appears to be of considerable commercial potential for the lettuce industry.

Over 700 measures of the level of ethylene in the atmosphere of fruit and vegetable holding areas in wholesale markets, distribution centres, supermarket retail stores and domestic refrigerators were taken over a 3-year period. The lowest ethylene levels were found in supermarket stores with a mean level of 0.017–0.035 L/L in produce receival, storage and display areas. Levels in the ambient air of wholesale markets and distribution centres were higher at about 0.06 L/L. Domestic refrigerators were grouped into those that contained or did not contain apples with the ethylene level being much higher at 0.20 L/L where apples were present and 0.029 L/L where apples were absent. Using a rating scale, which was developed from published literature on non-climacteric produce, of ≤0.015 L/L ethylene as a low level where less than 10% of potential postharvest life is lost and ≥0.1 L/L as a high level where there is higher than 30% loss of postharvest life, suggests that most produce during marketing is held in an ethylene atmosphere where 10–30% of potential postharvest life is lost.

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.