Green ripe fruit is a major quality problem for mangoes because it reduces their saleability, especially the Kensington Pride variety. Although green ripe fruit softens, the skin retains a green colour or appears motley green/yellow in colour. This fruit is certainly not in demand as consumers and retailers expect ripe Kensington Prides to have a yellow skin colour, preferably with some pink or red blush. Green fruit will generally be left on the retail shelf.
The change in skin colour from green to yellow typically occurs during ripening. It can be affected by both orchard management and postharvest handling practices. Research to investigate the cause of green ripe fruit was done back in the 1990’s and it is still very applicable today. Researchers studied several production factors that may have contributed to the green skin colour. Below were some of their findings:
Factors that cause green fruit
- Nitrogen - Orchards receiving high nitrogen applications often produce fruit with greener skin colour when ripe. Some nitrogen can be applied near flowering without having a large effect on skin colour.
- Water stress - Fruit from trees suffering water stress had more green colour on the skin at ripe
- Maturity – the amount of green colour on the skin of ripe fruit was lower in more mature fruit.
- Shade - in most instances, fruit that gets less sun has more green colour when ripe.
- Temperatures and Ethylene treatment during ripening have a large effect on the amount of green on ripe fruit. The optimum range for the development of yellow colour is 18-22°C. If fruit ripens at temperatures above 22°C or at temperatures below 18ºC, the amount of green on the skin can be higher. Three days exposure to 10 ppm ethylene gives less green colour than one day. However, ethylene concentrations higher than about 100 ppm can increase green colour if fruit is held at low temperatures (10-13°C).
- Ripening mangoes produces large amounts of carbon dioxide. Ripening rooms containing a lot of ripening fruit can result in the carbon dioxide concentrations reaching 4% or higher if there is poor ventilation in the rooms. Fruit ripened in 5% carbon dioxide can have more green colour. Therefore, it is important that the ripening rooms are well ventilated to prevent carbon dioxide getting too high.
- Factors that cause stress to fruit can increase the risk of green colour on ripe fruit. For example, excessive heat from disease control or disinfestation treatments can increase the green skin colour. Physical injury during harvesting and handling can also cause localised green areas on the ripe skin.
Yellow skin colour can be increased by:
- Avoid excessive nitrogen fertilisation
- Ensure that trees receive adequate water
- Maintain an open tree canopy and avoid crowding of trees to improve light penetration
- Harvest only mature fruit, and delay harvesting if green fruit is known to be a problem. Shaded fruit can be harvested later.
- Minimise the risk of fruit injury, especially during de-sapping and heat treatment.
- Ripen fruit at 18-22ºC with 10 ppm ethylene for two-three days.
- Do not ripen at low temperatures and do not use low temperatures with more than 50 ppm ethylene
- If ripening has to be delayed, hold the fruit at 10-13ºC, then ripen them under ideal conditions.
- Make sure that the temperature inside the pallet does not get too high during ripening. Either air stack the lidded trays or use a forced air ripening system.
This research was conducted by Dr. Peter Hofman, Rowland Holmes and Scott Ledger from the Agency for Food and Fibre Sciences division of the Queensland Department of Primary Industries in 1997 and revised in 2003. It has recently been reviewed by the technical adviser of project MG12001 – Mango Quality, Terry Campbell.