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Ethylene reduction process with ozone


Understanding ethylene

The ethylene reduction process in cold storage or controlled atmosphere storage is primarily aimed at slowing down the ripening and senescence of fruits and vegetables by managing the levels of ethylene gas. Ethylene is a natural plant hormone that promotes ripening, but high concentrations can lead to over-ripening or spoilage.

  • Production: Many fruits and vegetables produce ethylene as part of their natural ripening process. The rate of production can increase as they ripen, creating a feedback loop that accelerates spoilage.
  • Effect on produce: Ethylene not only affects the fruit or vegetable it’s produced from but can also influence surrounding produce, leading to quicker ripening, changes in color, texture, and flavor, and ultimately, spoilage.

Method for ethylene reduction with ozone

Ozone (O₃) reacts with ethylene (C₂H₄) to form carbon dioxide and water, effectively removing ethylene from the atmosphere. This process uses ozone generators to introduce controlled amounts of ozone into the storage environment. The reaction is:O_3 + C_2H_4 –> CO_2 + H_2O

Steps involved:

  1. Ozone generation:
    • Ozone is produced using an ozone generator, which converts oxygen (O₂) from the air or from a pure oxygen supply into ozone. These generators can be corona discharge or UV light-based.
  2. Ozone distribution:
    • The generated ozone is then distributed throughout the storage area. This can be done via fans or through direct injection into the air system of the storage facility.
  3. Controlled exposure:
    • The concentration of ozone must be carefully controlled. Too much ozone can damage the stored produce, while too little won’t effectively reduce ethylene levels. Typically, ozone levels are kept low, around 0.1 to 0.3 ppm (parts per million) for continuous application, or higher levels might be used intermittently when no workers are present.
  4. Reaction with ethylene:
    • Once ozone is distributed, it comes into contact with ethylene in the air, initiating the chemical reaction that converts ethylene into harmless compounds.
  5. Monitoring and adjustment:
    • Ethylene and ozone levels need to be monitored to ensure they remain within safe and effective ranges. Sensors for both gases are used to adjust the ozone generation as needed.
  6. Ventilation:
    • After treatment, particularly if higher levels of ozone were used, the area needs to be ventilated to remove excess ozone, which can be harmful to humans in high concentrations.

Benefits of using ozone for ethylene reduction

No residue: Ozone naturally decomposes back to oxygen, leaving no chemical residues on the produce.

  • Broad spectrum: Beyond ethylene, ozone also helps in managing other microbial contaminants, thus improving overall air quality and reducing spoilage risks.
  • Environmentally friendly: It’s a chemical-free approach to ethylene management, which is appealing for organic produce or in regions with strict chemical use regulations.

Implementation

  • Continuous low-level dosing: For ongoing ethylene management without human presence, low levels of ozone can be maintained.
  • Intermittent High-level treatment: When the storage area is empty (e.g., during cleaning or between batches), higher ozone concentrations can be applied to thoroughly sanitize the environment.

This method of ethylene reduction using ozone is particularly appreciated in the horticultural industry for its efficacy in maintaining the quality and extending the shelf life of stored fruits and vegetables.