Ethylene Inhibition and Control

The Dual Role of Ethylene in Postharvest Handling

• Useful: – Accelerates ripening – Chlorophyll degradation – Causes abscission • Problematic: – Accelerates ripening – Accelerates senescence and chlorophyll degradation – Causes abscission – Other undesirable changes

Ethylene Production Rates by Fresh Produce at 20°C (68°F)

Temperature Relative Humidity Ethylene Odour

Ethylene can be detrimental for Fruits.

Detrimental Ethylene Effects on Vegetables

The lower the temperature, the lower the amount of ethylene produced by fruits. At lower temperatures, vegetables are less affected, with the exceptions of lettuce and carrots.

Ethylene:- Accelerates ripening.
– Accelerates senescence.
– Causes abscission.
– Causes bitterness in carrots.

Manage Ethylene Effects

1. Temperature and Time
2. Avoidance
3. Removal
4. Inhibition of Production
5. Inhibition of Action
6. Germplasm Modification

Temperature and Time

Low temperature slows reaction rates by slowing enzyme activity.
Ethylene responses are slowed by low temperature.
Time is required for product to perceive ethylene and cause response.

– How long can a product be exposed before there is a detrimental effect?
– Ethylene concentration, temperature, time.

Avoidance

Keep ethylene sources away from sensitive products.
Ethylene sources include:
– Forklifts and floor polishers – Ethylene producing products
– Smoking
– Decaying Produce

Removal

Ventilation – about 1 air exchange per hour, fresh air.Measure ethylene concentrations to remain below the threshold.

Absorption (act. carbon, filters)
Oxidation – KMnO₄, U.V, Ozone.

See: http://postharvest.ucdavis.edu/yellowpages/?maincat=44 for a list of Ethylene scrubbers and action inhibitors.

Inhibition of Ethylene Production

– Low temperature- Low O₂
– Chemical inhibitors of enzymes
– AVG, AOA, Others.
– Antisense technology
– Gene/DNA inserted reverse order
– Nonfunctional
– Natural Mutants

Molecular Manipulation of Ripening

– Anti-sense ACC synthase; Anti-sense ACC oxidase.- Result – Fruits that ripen very slowly require ethylene treatment to ripen or to produce aroma volatiles.

Inhibition of Ethylene Action

– Low temperature
– High CO₂
– Low O₂
– STS – Silver thiosulphate (Cut nonedible flowers)
– Cyclopropenes
1-MCP (Smartfresh™; Ethylbloc™)

Inhibition of ethylene action
1-MCP (SmartFresh™) Treatment
• Gas liberated from a substrate in closed space much like an ethylene treatment
• Irreversibly binds to ethylene receptor
• Concentration sufficient to saturate receptors (~1000 ppb = 1 ppm )
• Treatment time sufficient for gas to penetrate tissues (hours)
• Treatment temperature (0-20°C)
• Single or multiple applications
• Product and stage of maturity

1-MCP and Melons

– Western shipping cantaloupes – not much benefit on firmness at storage temperature.
– Eastern shipping cantaloupes – Reduce softening at warm temperatures.- Galia; extend shelf-life, reduce firmness loss.
– Watermelon – Clear benefit; reduce firmness loss and internal breakdown

Fruits and SmartFresh™ (1-MCP)
SmartFresh™ is a powerful regulator of climacteric fruit ripening

Its use is complicated for fruit because results depend on:
– Fruit maturity/ripeness at application
– 1-MCP concentration and exposure time
– Temperature during and following treatment

Important to determine where SmartFresh™ can add value to the fruit category