Preventing soft landings and storage related disorders in export avocados

PRINCIPAL INVESTIGATORS: Dr Frans Kruger and Danie Lemmer
CONTACT DETAILS: +27 13 753 7000/ +27 83 391 5822/
DURATION: Four years
LEAD INSTITUTION: ARC–Institute for Tropical and Subtropical Crops
BENEFICIARY: The subtropical fruit sector

South Africa exports avocados to the same Northern Hemisphere markets at the same time of the year as South American fruit exporting countries. All of these countries share overlapping harvesting seasons, but the South American growing conditions are more favourable. As a result, the South African industry is under extreme pressure to deliver superior quality produce.

Factors that influence the respiration and softening rates of avocados

If the South African industry can minimise soft landings (which happens when the fruit ripens prematurely during storage and arrives soft in overseas markets), and ensure the supply of excellent quality hard export avocados, fruit can be marketed late in the season when the demand is big and the profit at its highest.

The storage related physiological and pathological disorders that develop during the exportation process, is another serious problem. However, there is a significant lack of information on how the different storage factors interact to influence respiration and softening rates and the development of physiological disorders of the fruit.

The issue was addressed in a project, jointly sponsored by the Post-Harvest Innovation Programme and the South African Avocado Growers’ Association (SAAGA). Dr Frans Kruger and Danie Lemmer led the study at the ARC-Institute for Tropical and Subtropical Crops (ITSC) in Nelspruit.

Trials conducted on export avocados over four seasons

  • Trials on the ‘Hass’ cultivar were focused on generating baseline information during the first season (2008).
  • ‘Hass’ avocados were stored in regular atmosphere conditions for thirty days at three maturity levels (moisture content: 75%, 70% and 65%) and at five temperature settings (8.0°C, 7.0°C, 6.0°C, 5.0°C and 4.0°C).
  • Respiration rates were determined every second day and flesh firmness was measured every fourth day.
  • Trials were repeated in the second season with the introduction of CA Smartfresh™.
  • The effect of temperature breaks on fruit quality was also determined. It mainly caused a drastic increase in pathological disorders.
  • During the third and fourth seasons, the ‘Fuerte’, ‘Pinkerton’, ‘Ryan’ and ‘Maluma’ cultivars were included in the study.

The outcome of export avocado research trials

  • The initial respiration rates of ‘Hass’, ‘Maluma’, and ‘Fuerte’ were higher than those of ‘Pinkerton’ and ‘Ryan’.
  • The respiration rate of ‘Pinkerton’ started to increase during the third week of storage, and the other four cultivars during the fourth week. However, the eventual respiration rate of ‘Pinkerton’ and ‘Ryan’ was the lowest at the end of the thirty-day storage simulation period.
  • In all cultivars, flesh firmness started to decline before the respiration rate increased.
  • Temperature breaks caused a significant increase in pathological disorders in all cultivars and a higher incidence of grey pulp in ‘Fuerte’.
  • A Smartfresh™ application successfully reduced the occurrence of grey pulp and pathological problems in all cultivars.

Outcome of study and benefits to industry

  • The scientific data generated by this project provides a major breakthrough. For the first time, it can provide the evidence required to help settle commercial claims, e.g. regarding ‘soft landings’.
  • The project focused on quantifying the effect of cold chain breaks on the respiration and softening rates of export avocados. The information is now being used to establish the ideal temperature settings and storage regimes for the ‘Pinkerton’ cultivar, which is prone to develop chilling injury.
  • The study clarified the physiological reasons why it is essential to reduce the initial respiration rate of the new ‘Maluma’ cultivar as soon as possible after harvest.
  • Smartfresh™ applications are also being refined to achieve better ripening profiles in European markets.
  • The full value of the project will become apparent over the next few seasons with the introduction of additional storage applications.