Respiratory and ethylene activity and heat release of Pears Cv. yanis, treated with ethylene inhibitor depending on cooling mode

Abstract

Pear is a valuable fruit crop which, after apple trees, occupies a leading place in the structure of Ukrainian horticulture. Pear fruit are more difficult to store than apples and they are sensitive to improper conditions in the fruit storage. Too early picked fruit will wither and, if harvested too late, they will be more susceptible to rot, flesh browning and taste deterioration during storage. Rapid post-harvest cooling reduces fruit susceptibility to physiological disorders, while a delay in setting a recommended temperature leads to premature ripeness.

The optimum storage temperature of pears is in the range from minus 1 °C to 0 °C and its excess by only 1 °C from a recommended one for a pomological cultivar reduces the storage duration by 20 %. The elimination of a negative impact of inappropriate storage conditions, in particular the untimely achievement of a recommended temperature and atmosphere in the storage is carried out by a post-harvest treatment with 1-methylcyclopropene (1-MCP).

The optimal harvest time is important for pears, because the treatment of prematurely harvested fruit slows down the ripening process significantly and pears do not reach a desired quality, and if they are harvested too late, the effect of 1-MCP will be insufficient. During respiration, the fruit emit carbon dioxide, water and heat. The treatment of 1-MCP reduces ethylene activity and respiration intensity, the heat output will be lower as well as energy consumption - up to 35 %, respectively, to maintain the temperature in the fruit storage.

The purpose of this study was to improve the storage technology of pears, cv. Yanis, of different picking dates and to establish the effect of a harvest time, the delay of post-harvest cooling and the treatment of 1-MCP on ethylene activity, respiration rate and fruit heat release. The research was conducted in the storage seasons of 2013/2014 and 2014/2015 at the Department of Fruit Growing and Viticulture of Uman National University of Horticulture. Yanis pears were collected from trees on a quince rootstock A (planting of 2007) and stored in a branch of the Department – the farm «Yanis» of Khotyn district, Chernivtsi region. The soil management system between the rows was sod-humus and herbicide fallow in the stem strips.

The fruit were collected in two terms: the first term – the onset of harvesting maturity (the beginning of harvest maturity, mass picking) and the second term – a week later (full harvest maturity, delayed picking). After picking, half of the fruit were immediately cooled at a temperature of 5±1 °C and a relative humidity of 85–90 % (immediate cooling), the rest was cooled similarly after a 24-hour exposure at 18…20 °C and a relative humidity of 55…60 % (cooling delay). The following day, the fruit were treated with a 1-MCP dose of 500 ppb (0.034 g/m³ SmartFresh). After a 24 hour- exposure, the container was removed, the treated and control fruit were stored in a refrigerated chamber at a temperature of 2±0.5 °C and a relative humidity of 85–90 % (untreated fruits - control).

The temperature in the chamber was monitored with alcohol thermometers and automatically, and the relative humidity – with a hygrometer. An ethylene production rate was periodically measured by a portable analyzer ICA-56 at 18…20 °C, the fruit respiration – by the amount of carbon dioxide, and the heat release was calculated from the amount of CO₂ emitted during respiration.

Regardless of the picking date, at the end of a six month-storage, immediately cooled Yanis pears emit ethylene by 1.2–1.3 times less. 1-MCP treatment more effectively slows down the synthesis of ethylene in mass picked fruits with an indicator decrease by 1.8 times for delayed cooled and 2.2 times for immediately cooled pears, as compared with untreated fruit (1.2 and 1.7 times for delayed picked fruit, respectively). The ethylene activity of mass picked fruit was 1.4 times lower with immediate cooling and it was 1.2–2.7 times lower in the case of post-harvest treatment of 1-MCP. The change in ethylene activity of freshly harvested pears is mainly determined by the harvest time (influence of 51.5 %), post-harvest treatment of 1-MCP (24.6) and post-harvest cooling (11.7 %) and after six-month storage – mainly by treatment of 1-MCP (44.6) and cooling (29.7) with significantly less influence of the harvested period (14.5 %).

At the end of six-month storage, fruit respiration and heat release do not significantly depend on the harvest time and a post-harvest cooling mode. Post-harvest 1-MCP treatment reduces the intensity of fruit respiration by 1.5 times and the heat release – by 1.6 times.