Ethylene Treatments for Ripening & Degreening Ethylene Ethylene Ethylene

Ethylene Treatments Ethylene for Ripening & • The most important plant hormone in postharvest horticulture. Degreening • Has a slight sweetish smell.

Mark A. Ritenour - UF IRREC • Not toxic - but can cause asphyxiation & if the gas displaces oxygen in the Jeffrey K. Brecht - UF Gainesville atmosphere.

Ethylene • Has anesthetic properties. • It is active at < 0.1 ppm (some say as low as 0.005 ppm). • Explosive at concentrations between 3.1% and 32% (31,000 to 320,000 ppm) by volume in air.

Ethylene Ethylene Production • Key hormone coordinating physical and Sensitivity and biochemical changes associated • Produced by all harvested commodities. with ripening of climacteric fruits. • Quantities vary depending on organ type. • E.g. “gassing” to ripen bananas, tomatoes, etc. • Effects desirable or deleterious. • Also stimulates respiration and • Commodities producing little or no hastens senescence in non- ethylene may respond adversely to climacteric crops. exposure. • E.g. degreening in citrus.

1 (µl C2H4/kg-hr Class at 20oC (68oF) Commodities Very Low < 0.1 Artichoke, asparagus, cauliflower, cherry, citrus Ethylene Pollution Sources fruits, grape, jujube, strawberry, pomegranate, leafy vegetables, root vegetables, potato, • Plants (e.g., ripening fruits). most cut flowers • Decomposition of organic materials (incl. oil, Low 0.1 - 1.0 Blackberry, blueberry, casaba melon, cranberry, coal, gas). cucumber, eggplant, okra, olive, pepper (sweet • Internal combustion engines. and chili), persimmon, pineapple, pumpkin, • Decomposing/rotting produce. raspberry, tamarillo, watermelon Moderate 1.0 - 10.0 Banana, fig, guava, honeydew melon, lychee, • Heating systems. mango, plantain, tomato • Cigarette or other smoke. High 10.0 - 100.0 Apple, apricot, avocado, cantaloupe, feijoa, • Tar-based light ballasts. kiwifruit, nectarine, papaya, peach, pear, plum • Some rubber materials when exposed to UV light. Very High > 100.0 Cherimoya, mammee apple, passion fruit, sapote

Ethylene Concentrations Ethylene Effects Sample Location Range (ppm) Mean (ppm) Field Trace-0.12 Field to cooler 0.13-0.11 0.07 • Ripening and color changes in many fruits. Holding before cooling 0.01-0.80 0.16 – Promotes faster, more uniform fruit ripening. After cooling 0.01-0.29 0.12 • Loss of green color in citrus (degreening). Cold storage 0.01-2.78 0.33 • Loosens fruits & nuts for mechanical Inside rail cars 0.01-0.19 0.06 Inside trucks 0.04-0.22 0.08 harvest Distribution warehouses 0.03-2.49 0.25 – Abscission Retail storage 0.06-2.88 0.41 Home refrigerator 0.02-1.58 0.25

Ethylene – Negative Effects Ethylene – Negative Effects • Accelerated ripening & softening of fruits • Toughening (lignification) of asparagus. (e.g. kiwifruit) during storage. • Stimulated sprouting of potatoes (or • Hastens senescence. inhibition if exposure prolonged and at high – E.g., yellowing of broccoli or cucumbers. concentrations). • Induction of stress metabolites. • Abscission of leaves and flowers (cabbage, – Formation of a bitter-tasting chemical cauliflower, ornamentals). (isocoumarin) in carrots. • Reduced storage life and quality of – Promotes phenolic metabolism related to cut flowers (“sleepiness” in carnations). lignification and oxidative browning.

2 Ethylene – Negative Effects Factors Affecting Ethylene • Causes or promotes some physiological Production & Action disorder. • Genotype (species and cultivar). – E.g., Russet spotting on lettuce. – Apple vs. tomato vs. citrus vs. strawberry etc. – ‘Sleepiness’ of carnations (the – Different cultivars (e.g., of avocado) may have bloom does not open). different ethylene production & ripening rates. – Bulb crops: inhibition of shoot • Physiological age. and root elongation; – Ethylene production and response of gummosis; bud necrosis and flower bud climacteric fruits depends on their blasting. physiological age.

Factors Affecting Ethylene Death Initiation Development Production & Action Growth •Temperature. Maturation – Peak ethylene production at ~25°C. – Ethylene production inhibited above 30°C. Physiological • Oxygen level.

Maturity – Reduced O2 (<8%) reduces ethylene action and production rates. Ripening – Elevated O2 (>21%) stimulates ethylene production and action. Senescence

Factors Affecting Ethylene Factors Affecting Ethylene Production & Action Production & Action

•CO2 level. • Other hydrocarbons. –CO2 competitively inhibits ethylene action. – Propylene, carbon monoxide, acetylene, etc. • Inhibition of ripening at >1.0%. can enhance ethylene production by fruits and • Inhibition of degreening at >0.1%. mimic ethylene action.

–CO2 injury can induce elevated ethylene • Stresses. production. – Physical damage, diseases, fumigation, • Exogenous ethylene. irradiation, etc. are all stresses that stimulate – Ethylene exposure induces climacteric fruits to ethylene production. initiate autocatalytic ethylene production.

3 Ripening – Fruit Changes Ripening – Fruit Changes

• Softening of the fruit flesh. • Change in color. • Change in texture from firm to soft. • Loss of chlorophyll. • A function of cell wall and middle lamella • Synthesis of yellow and red pigments. dissolution. • Carotenoids - tomato, peach. Chloroplast • Changes in the synthesis and excretion conversion to chromoplasts. of surface waxes. • Anthocyanins (pink, red, purple) – • E.g. development of the “bloom” on grapes, cherries, apples, blueberries. plums, etc.

Ripening – Fruit Changes Commercial Use of Ethylene

• Changes in aroma and flavor • Methods of application (compositional changes). – Cylinders of ethylene or banana gas • Conversion of starch to sugar (e.g. sucrose, (C2H4 in N or CO2) with flowmeters. fructose, glucose). – Ethylene generators (liquid ethanol plus • Decreases in acidity. catalyst → C2H4). • Production of aroma & flavor volatiles – Ethylene-releasing chemicals. (alcohol esters). • E.g., Ethephon (2-chloroethane-phosphonic • Polymerization of tannins (reduced acid). Breaks down at pH>3.5 to release astringency, e.g. persimmons). ethylene.

Commercial Use of Ethylene Ethylene for Ripening

• Ethylene concentration and duration of Ethylene can be used to ripen treatment a variety of commodities – Physiological responses saturated at 100 ppm. • Bananas • Mangos – Mature climacteric fruit should initiate •Tomatoes endogenous ethylene production within no more • Pears than 72 hours. • Avocadoes • Papayas – Degreening should continue for no more than • Kiwifruits 72 hours or risk increased peel senescence and • Persimmons decay. • Melons

4 Commercial Use of Ethylene Tomato Banana Avocado Kiwifruit

Temp. 68-70F 58-65F 60-65F 32-68F RH 90-95% Ethylene 100-150 10-100 100 (ppm)

Ventilation Keep CO2 < 1% (approx 1 room exchange/h) Circulation 0.1 to 0.2 ft3 per min. per. lb. product. Duration 72-84 h 24-48 h 8-48 h 12 h

Ethylene Ripening

Banana pressure ripening room

5 Degreening of Citrus • Recommended conditions (Florida) – 82 to 85oF (28 to 29°C). – 90 to 96% RH. – 5 ppm ethylene. – Air circulation = 10 ft3 per min. per box. – Ventilation = 1 air change per hour.

• Rate of degreening is slowed if CO2 reaches 0.1%, and will nearly stop if it reaches > 1%.

Degreening of Citrus • Recommended conditions (California) – 68 to 70oF (20 to 21°C). – 90 RH. – 5 ppm ethylene. – Air circulation = 0.1 ft3 per min. per. lb. product. – Ventilation = 1 to 2 air changes per hour.

Ethylene Biosynthesis

Methionine S-Adenosylmethionine (MET) (SAM) Thank You ACC Synthase 1-aminocyclopropane-1-carboxylic acid (ACC) – Can be transported in plant UF Postharvest Website

http://postharvest.ifas.ufl.edu ACC Oxidase Ethylene

(C2H4)

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