Are your mangoes being treated well as they travel by road or rail from farm to market? Are the conditions in the refrigerated container controlling the quality of the fruit as you expected, or are your fruit ripening too quickly or getting damaged because the temperatures are too low? Are your transport conditions being monitored so you can identify if improvements need to be made to prevent loss of quality and value?
Controlling fruit temperatures is the most important tool for preventing quality loss during transport. We have been monitoring conditions of mangoes in refrigerated road or rail containers during transport from the Northern Territory to southern markets over the last six years. We have found that:
- Fruit temperatures can be more than 10°C warmer near the back of the container compared with near the front, and vice versa (Figure 1)
- Fruit can be exposed to air temperatures as low as 7°C even though the container is set at 13°C (Figure 2). This is more likely if fruit temperature at loading is more than 3°C warmer compared with the container set temperature
- The typical fruit temperature in the majority of the load are usually higher than the temperature of the air from the refrigeration unit
- The temperature in the pallet closest to the door is not a good indicator of average fruit temperatures for the whole load.
So, container set temperatures do not accurately indicate the fruit temperature during transport. It is important to monitor temperatures in the load to help identify the causes of poor quality when the fruit are ripe, and to determine where improvements are required. Our recommendations for monitoring fruit temperatures include:
- Monitor temperatures in several locations within the load. As a minimum, loggers should be placed in the second row from the front and in the second row from the back, in trays at least four layers down from the top, and at least 50 cm from the walls of the container
- Ideally, fruit pulp temperatures should be measured, but these loggers require a probe and are more expensive than air temperature loggers. Pulp and air temperatures within the bulk of the load (typically where there is less airflow) are usually within 1-2°C, so in most instances air temperature loggers can be used.
There are many brands of temperature loggers. Technology has advanced to the stage where wireless temperature loggers are an affordable option. These download data from the logger to an internet gateway with no need to physically retrieve the logger to download the data. The data is instantly available on a secure website, often in the form of a temperature graph and with associated email alerts when consignments have been exposed to undesirable temperature conditions.
Current recommendations for journeys longer than three days includes cooling the fruit to about 13°C, transporting at this temperature, then ripening at 18-20°C at the markets. However, starting the ripening process in the refrigerated container (in-transit ripening) can save ripening time in the markets, and energy costs (less cooling) on farm and during transport. For mangoes, this involves cooling the fruit to 16-18°C, transporting at this temperature, and maintaining ethylene concentrations in the transport container between 10-50 parts per million (ppm) for at least two days.
There are two key conditions to successful in-transit ripening:
- Fruit must be cooled to less than 18°C before loading, then maintained at or below 18°C during transport
- Carbon dioxide (CO2) concentrations inside the refrigerated container can increase to more than 15% because of respiration of the fruit. CO2 concentrations need to be measured, and controlled to below 4% (depending on cultivar) to prevent loss of ripe fruit quality and to minimise worker risks. CO2 loggers are more expensive than temperature loggers, but only one logger per container would be required. This can be placed on the top of a pallet anywhere in the load.
Monitoring ethylene concentrations is also important during in-transit ripening, but ethylene loggers are considerably more expensive than CO2 loggers. More accurate and cheaper ethylene monitoring systems may be available in the future, which we intend to evaluate when available.
Fruit temperatures after harvest are often not ideal—what you expect is often not what you get. Regular monitoring of fruit temperatures from harvest onwards is a key component of ensuring your fruit can reach maximum quality when ripe. It is also key to on-going improvement—we cannot fix it if we do not know it is broken. Cost-effective systems for routine temperature monitoring are now available. Regular monitoring and a common commitment from key post-farm gate supply chain members will help your fruit ripen to the best quality every time.
In-transit ripening can reduce post-harvest costs, but regular monitoring of temperature and atmosphere conditions are essential to success.
Article submitted by Peter Hofman and Andrew Macnish from Queensland Department of Agriculture and Fisheries (DAF) and Daryl Joyce from DAF and the University of Queensland.
Acknowledgements: This has been a team approach over many years. We thank mango growers, transporters and ripeners, Khamla Mott (PhD student) and Professor Bhesh Bhandari (ethylene release systems) from the University of Queensland, and Dr Roberto Marques.
Project MG12016 is funded by Hort Innovation using voluntary contributions from Piñata Farms Pty Ltd and matched funds from the Australian Government. The Queensland Government has also co-funded the project through the Department of Agriculture and Fisheries. The Northern Territory Department of Primary Industries and Resources is providing support for the PhD stipend. Additionally, the generous cooperation of Honey Gold growers and Piñata Farms staff is gratefully acknowledged.