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Recommendations for Maintaining Postharvest Quality

 Keri L. Morrelli and Adel A. Kader
Department of Plant Sciences, University of California, Davis, CA 95616

Maturity can be judged by the angularity of the fingers. Plantains are harvested mature-green and may or may not be ripened upon arrival at destination markets since plantains are eaten both at the mature-green stage and when fully yellow.

Quality Indices
  • Finger size (minimum length of 22 cm = 9 inches)
  • Freedom from mechanical damage, scars, insect damage, disease and chemical residues.

Optimum Temperature
7.2 – 10˚C (45-50˚F) for up to 7 days
10 – 12˚C (50-54˚F) for longer than 7 days

Optimum Relative Humidity
90-95%

Rates of Respiration Production
Temperature 7.2°C(45°F) 10°C(50°F) 12.5°C(54.5°F) 14°C(57.2°F) 20°C(68°F)
ml CO2/kg·hr1, 2
3-21
2-15
6-15
8-12
7-107

1
Low end for mature-green plantains and high end for ripening plantains.
2To calculate heat production multiply ml CO2/kg·h by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production
Temperature 7.2°C(45°F) 10°C(50°F) 12.5°C(54.5°F) 14°C(57.2°F) 20°C(68°F)
µl C2H4/kg·hr1
0.01-0.05
0.01-0.26
0.01-0.11
0.01-0.12
0.01-2.58
1Low end for mature-green plantains and high end for ripening plantains.

Responses to Ethylene
Ethylene stimulates ripening of plantains. Thus, plantains that are marketed mature-green should be protected from exposure to ethylene. Plantains that are marketed ripe should be ripened with bananas (exposure to 100-150 ppm ethylene for 24-48 hours at 15-20°C = 59-68°F and 90-95% relative humidity).

Responses to Controlled Atmospheres (CA)
  • Optimum CA: 2% O2 and 5-10% CO2
  • CA delays ripening, reduces respiration and ethylene production rates, and maintains overall appearance of the fruit.
  • CA may decrease the occurrence of subepidermal browning at marginally low temperatures.

Physiological Disorders
Chilling Injury. Symptoms include peel browning, dull or smokey peel coloration, subepidermal vascular browning, abnormal ripening (possible acceleration); and in severe cases failure to ripen. Chilling injury results from exposure of plantains to temperatures less than or equal to 7.2 °C (45°F) for 7 or more days, depending on cultivar, maturity, and temperature. Chilled fruit are more sensitive to mechanical damage and postharvest decay.

Physical Disorders
Skin abrasions. Abrasions result from skin scuffing against other fruit, surfaces of handling equipment, or shipping boxes. When exposed to low relative humidity conditions (<90%), water loss from scuffed areas is accelerated and peel color turns brown and in severe cases black, which is similar to severe peel browning associated with chilling injury.
Impact bruising. Dropping of plantains may induce browning of the flesh with or without damage to the skin. In some cases, damaged areas may become infected with fungal growth.

Pathological Disorders
Crown rot. This disease is caused by one or more of the following fungi: Thielaviopsis paradoxa, Lasiodiplodia theobromae, Colletotrichum musae, Deightonialla torulosa, and Fusarium roseum – which attack the cut surface of the hands. From the rotting hand tissue the fungi grow into the finger neck and with time, down into the fruit.
Anthracnose. Caused by Colletotrichum musae, becomes evident as the bananas ripen, especially in wounds and skin splits.
Stem-end rot. Caused by Lasiodiplodia theobromae and/or Thielaviopsis paradoxa, which enter through the cut stem or hand. The invaded flesh becomes soft and water-soaked.
Cigar-end rot. Caused by Verticillium theobromae and/or Trachysphaera fructigena. The rotted portion of the plantain finger is dry and tends to adhere to fruits (appears similar to the ash of a cigar).
Control strategies. Minimizing bruising; prompt cooling to 12°C (54°F); proper sanitation of handling facilities; hot water treatments (such as 5 minutes in 50°C (122°F) water and/or fungicide (such as Imazalil) treatment to control crown rot.

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