Researchers discover key to reducing skin damage to Honey Gold

Researchers investigating the causes of underskin browning (USB) on Honey Gold mangoes have found that spirt sap from mangoes harvested in the afternoon is more likely to cause the skin disorder than sap from mangoes harvested in the morning.

Typical underskin browning. Notice that there is slight physical damage in the USB area. USB often develops from sites of physical damage, often caused during long distance roadfreight.

Typical underskin browning. Notice that there is slight physical damage in the USB area. USB often develops from sites of physical damage, often caused during long distance roadfreight.

The ongoing research project by the Queensland Department of Agriculture and Fisheries ‘Improving consumer appeal of Honey Gold mango by reducing underskin browning’ has been exploring ways to reduce the incidence of USB on the Honey Gold variety. Initial findings led researchers to examine ways to produce more robust fruit and they have since uncovered numerous findings that, while yet to be scientifically proven, could mean big changes for the industry.

Gavin Scurr, Managing Director of Pinata Farms said that the way mangoes are harvested and handled has fundamentally changed due to the project.

“Before the start of the project, our losses due to underskin browning were up to 20% of our Northern Territory crop. Since initiating the project, we have adopted the recommendations and have reduced our USB losses to below 1%. As well as harvesting at night, we have designed and built a harvest aid to carry fruit with conveyer belts to the baths due to the outcomes of this project.” Mr Scurr said.

The fruit above was harvested at 10am and the fruit below at 10pm. The fruit were lightly abraded with sandpaper, held below 14ºC for about six days then ripened. The USB develops around the abrasion sites in sensitive fruit.’

The fruit above was harvested at 10am and the fruit below at 10pm. The fruit were lightly abraded with sandpaper, held below 14ºC for about six days then ripened. The USB develops around the abrasion sites in sensitive fruit.’

USB is a mango skin disorder that appears as a bruise like symptom underneath the skin. While several Australian mango cultivars are susceptible to USB, Honey Gold is the most sensitive.

Some of the key finds include:

The percentage of fruit with commercially significant USB (more than one cm2) when harvested at different times during the day and night. The USB occurred either around abraded sites on the skin or on non-abraded parts of the skin. These areas were likely damaged during road freight from Katherine to Brisbane.

The percentage of fruit with commercially significant USB (more than one cm2) when harvested at different times during the day and night. The USB occurred either around abraded sites on the skin or on non-abraded parts of the skin. These areas were likely damaged during road freight from Katherine to Brisbane.

  • Harvesting mangoes between 10pm and 6am significantly reduced the incidence of USB. Based on these findings, Piñata Farms harvested close to 80% of their Katherine Honey Gold crop at night during the 2014/15 season and saw their lowest commercial USB losses on record.
  • Honey Gold grown in the hotter production areas of the Northern Territory and north Queensland are more susceptible to skin damage than those grown in colder areas.
  • Road freight at temperatures lower than 16°C increases incidence of USB
  • Mangoes harvested in the afternoons are more susceptible to the skin conditions when compared with mangoes harvested during the night or morning
  • Ooze sap collected from either morning or afternoon-harvested fruit does not cause USB
  • Holding fruit for at least 24 hours between harvest and cooling can reduce USB development
  • Only spirt sap from afternoon-harvested fruit results in USB-like symptoms.

Some of these findings have been made through tests on abraded mango skin by applying small amounts of mango sap or by holding the fruit at below optimum temperatures so see at what points the fruit becomes susceptible to the disorder.

Researcher are now analysing the sap to find out what components cause the damage and plan to test whether these effects apply to other Australian cultivars in coming seasons.

This project, MG13016 Improving consumer appeal of Honey Gold mango by reducing underskin browning has been funded by Horticulture Innovation Australia Ltd with co-investment from Piñata Farms and funds from the Australian Government. Project partners include Tropical Horticulture Consulting and the University of Queensland.

Peter Hofman
Senior Principal Horticulturist
Deartment of Agriculture and Fisheries
Queensland