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Postharvest Handling of Papaya

Postharvest handling of the papaya (Carica papaya L.) requires care and attention to detail. Papaya is susceptible to several factors that can reduce its marketability, including extreme or fluctuating temperature, moisture, disease, and mechanical damage. Exposure to these factors‹through improper harvesting, decontamination, and inappropriate handling‹can cause under- or over-ripening, inconsistent quality, and poor flavor and result in high postharvest losses. If properly cared for, papayas can sustain a shelf life of four to six days under ambient tropical conditions (25oC to 28oC), or up to three weeks under lower temperatures (10oC to 12oC).

Export Criteria

Papayas intended for export are carefully graded by size and stage of ripeness. Fruit should be uniform in size and ripeness and be free from bruises, blemishes, and insect damage. Most importers also require that papayas be mostly yellow and have a uniform softness; a smooth, unblemished skin; and a minimum sugar content of 12 Brix.

When harvested, papayas are green with a stripe of yellow at their base; they ripen during transport or are commercially ripened on arrival. As papaya ripens, skin color changes from green to yellow, and the fruit becomes softer and develops a fruity aroma.

Papayas are normally sold to consumers when they are at least one-quarter ripe. Optimal ripeness occurs at the three-quarter stage, when the fruit bears a yellow-orange peel and an orange-red pulp. Peel color may vary from yellow to reddish-orange, depending on the variety of papaya.

Three Hawaiian varieties‹Solo Sunrise, Kapoho, and Waimanalo‹ are the most popular, and Solo Sunrise is the most important in world trade. Papayas of all three varieties are relatively small, normally weighing from 250 to 500 grams. Some countries are beginning to produce and export several Taiwanese varieties, which tend to be larger than those from Hawaii. Some markets require very large, local varieties of papaya. In the Latin market in the United States, for example, papayas weigh about 3 kilograms.

Fruit shape is not a function of variety but of the sex of the plant the fruit grows on. Round fruit comes from a female plant, and traditional pear-shaped fruit comes from a hermaphrodite plant. Because the market prefers pear-shaped fruit, female plants are normally removed from production as soon as their sex is known.

Commercial papayas are normally harvested 9 to 10 months after being transplanted from nurseries. Fruit should be harvested when skin color changes from dark green to light green and when one yellow streak begins developing from the base of the fruit upward. Fruit in this condition will continue to ripen normally after harvest. If harvested before or after this stage, however, papayas will either fail to ripen completely (if picked too early) or become more susceptible to damage and bruising during handling (if picked too late). Because their ideal stage of maturity is so short-lived, papayas are usually harvested three or four times a week. Leaving fruit as long as five to seven days between harvests can lead to its rejection as over-ripe.

Papayas are harvested by hand alone or with knives or specialized tools, depending on the size and age of the tree. When harvesting papayas by hand or with knives, harvesters snap or cut the stem directly adjacent to the tree and immediately trim it flush against the top of the fruit. To reach fruit at the top of tall trees, harvesters use a long pole with a small hoop and a small, mesh bag at the end. Above the hoop sits a horizontal blade, which the harvester positions below the stem of the fruit and moves upward to detach the papaya from the tree and catch it in the mesh bag below. Two or three fruits are collected at a time in this manner. Bags should be shallow to prevent overfilling and should be made of a soft material to prevent damage to the papaya skin.

After harvest, the fruit are placed gently‹never thrown or dropped‹in single layers in shallow, light-colored plastic field crates, preferably with a foam layer for cushioning. Mesh bags, sacks, or baskets are unacceptable for papaya transport because of the fruit's high susceptibility to bruising. Care should be taken during transport to minimize jostling of the fruit, and all stems should be trimmed to ensure that no stem-to-fruit rubbing occurs. Prior to collection, field crates and fruit should be left in shaded conditions, protected from the sun and rain.

Grading and packing should be carried out as soon as possible after harvest, normally within three hours, after which time the fruit should be kept at ambient tropical conditions (25oC to 28oC) to continue ripening, or cooled and stored at 10oC to 12oC.

The key packing processes followed in exporting papayas are shown below.

Pre-grading: Fruit that fail to meet export specifications (see Export Criteria above) should be removed before the washing and decontamination stages and packed later or in a different packing line. Failed fruit may be acceptable for sale on the domestic market.

• Over-ripeness-fruit exhibits localized softening or has more than three yellow stripes at its base.
  
  
• Under-ripeness-fruit has no yellow stripes.
  
  
• Mechanical damage-fruit has been damaged by knives, harvesting poles, rubbing from the crate, and the like.
  
  
• Washing: Pre-graded fruit should be placed in a water tank to remove latex and debris. In larger operations, fruit is washed with water in a separate tank or with overhead sprays before being passed to the main wash tank. Normally papayas require no additional cleaning, but some may benefit from a careful wiping with a soft cloth. Fruit can also be cleaned with rotating brushes if the brushes are very soft, but simple movement through a water tank for 10 to 15 minutes generally suffices.
  

• Quarantine/fungicide treatment: Depending on the papayas' origin, some importing countries require that the fruits be treated for fruit flies. Treatments are determined by importing-country requirements, but may include long-exposure, hot-water dip treatment, or vapor heat treatment. Papayas that travel from Hawaii to Japan must undergo vapor heat treatment.
  
  
• Disease control: Disease control begins in the field. In some cases, and where permitted, postharvest treatments can be used to help prevent the development of anthracnose and phytophthora neck rot.
  
  
• Grading: After pre-grading, washing, and fungicide treatment, the papayas are left to dry and then are graded for packing. Graders remove any fruit that shows signs of fresh mechanical damage or any of the conditions that qualify the fruit for rejection in the pre-grading stage. Remaining papayas are classified for packing based on size, stage of ripeness, and, if applicable, shape. Fruits of different shape may not be mixed in the same carton.
  

• Small: 13 to 16 count (308 to 250 grams);
  
• Medium: 9 to 12 count (440 to 330 grams);
  
• Large: 6 to 8 count (666 to 500 grams).
  

Papayas are best packed on their sides, in rows, with the stem ends at an angle; interlocking rows support one another. Papayas should not be packed on their bases because they soften from the base up. Packers should guard against overfilling the cartons.

The packing cartons should be one-piece, self-locking, or two-piece, full telescopic units, and should have a bursting strength of 200 to 250 pounds per square inch. All are made of fiberboard. Ventilation holes must be provided to allow for both horizontal and vertical cooling. Suggested external dimensions are 39.5 by 29.5 by 10.5 centimeters (length by width by height). In addition, cartons should be compatible with the importing country's palletization system. The carton suggested above fits the 1.0-by-1.2-meter International Standards Organization pallet used in Europe.

• Names of exporter and importer;
  
• Country of origin;
  
• Contents, variety, and net weight; and
  
• Grade, size, and ripeness at packing.
  

Papayas can be transported by sea when they are shipped at optimal harvest maturity‹that is, when they exhibit one or two yellow streaks. Fruit should be pre-cooled (preferably with forced air) before loading and conditions in the reefer container should be set at 10oC to 12oC with 50 percent ventilation. Pre-cooling and palletization are essential to prolong shelf life and prevent bruising during shipping. Equally important, palletization is a very cost-effective means of transporting fruit, as it helps minimize labor costs during unloading.

Disease control is critical for papayas that are shipped by sea, particularly to prevent anthracnose and phytophthora. Color development during sea shipment usually increases from 10 to 40 percent over 10 days at 12oC, and increases further during the customs, clearance, and delivery periods. When possible, containers should be delivered to the buyer to ensure cold-chain maintenance.

Fruit harvested at the recommended harvest stage (one yellow stripe) will ripen to 60 to 70 percent yellow within four to six days under ambient tropical conditions (25oC to 28oC). When stored at low temperature (10oC to 12oC), fruit harvested at the one-stripe stage will last for 14 to 21 days if postharvest disease incidence can be controlled. Papayas harvested at more advanced stages of ripening will display a significantly reduced storage life. (Storage life also varies depending on variety of fruit and growing conditions.)

Because papayas produce ethylene when they ripen, they should not be stored or shipped with ethylene-sensitive produce. As noted earlier, papayas are particularly susceptible to postharvest losses because they are easily damaged and infected by disease. Measures papaya handlers can take to control fruit loss are shown below, by risk factor.

• Mechanical damage: Many factors contribute to papaya skin damage, including the harvesting tool used, dropping of fruit into crates, overfilling of crates, and jostling of fruit during field transportation. During ripening, bruised areas will develop into soft, dark regions that are susceptible to secondary microbial infection. Similar problems can result from poor handling during washing, grading, and packing.
  Papaya handlers can minimize fruit damage by taking protective measures throughout all handling stages. Staff should be trained in proper harvesting techniques. As noted earlier, stems should be removed in the field to prevent puncturing or scratching of adjacent fruit, and fruit should never be thrown or dropped. In addition, transporters should drive slowly and carefully when taking fruit from the field to the packing house.
  At the packing house, crates should include foam in their base and contain only one layer of fruit. In automated operations, all machinery should be padded where possible. Palletized systems are preferable for moving produce in both field crates and final packages.
  

• Pathological factors: Anthrac-nose is prevalent in papayas during long-term storage, particularly as a result of orchard humidity, inappropriate pre-harvest disease control, or other poor orchard management. The presence of the disease is characterized by small black or light-brown spots that gradually grow and may coalesce and sink.
  Anthracnose can be controlled or reduced with pre-harvest sprays, which vary according to importer market. In operations that use pre-harvest sprays, postharvest control should consist of a cold-water dip or spray containing 0.05 percent thiabendazole solution and surfactant. (Before using any chemicals in the field or the packhouse on papaya for export, growers and packers should consult importing- and exporting-country legislation.)
  Where no pre-harvest sprays are used and anthracnose is present in the orchard, the cold-water dip may be insufficient to disinfect the fruit. In that case, harvesters should use a hot-water treatment for 20 minutes at 46oC. Specialized equipment is needed during hot-water treatments to maintain proper temperature and water circulation. Regulation is necessary because temperature fluctuations will reduce the treatmentıs effectiveness and may damage the fruit.
  Phytophthora can attack papayas during long-term storage at low temperatures if an orchard's disease-control systems are not in operation. Phytophthora is characterized by circular, translucent lesions that develop with gray surface mycelia. The disease is particularly apparent around the fruit's peduncle.
  

• Low temperatures: Storing unripe papayas at temperatures below 10oC will cause chilling injuries. Indications of chilling injury are surface pitting, discoloration of the peel and flesh, incomplete ripening, poor flavor, and increased susceptibility to disease. Although ripe papayas can be stored successfully below 10oC, transporting ripe fruit is not recommended because of increased susceptibility to mechanical damage and bruising.
  

• Small: 13 to 16 count (308 to 250 grams);
  
• Medium: 9 to 12 count (440 to 330 grams); and
  
• Large: 6 to 8 count (666 to 500 grams).
  

• No latex stains or surface debris;
  
• No wounds from harvesting or handling, including punctures, scratches, or bruises;
  
• No scars or residue from insects or sprays; and
  
• No fruit above the required color stage for shipment.
  

Selected markets and importers require medium-sized and large fruit, particularly for ethnic or catering markets. Hermaphrodite fruit are preferred because large female fruit show a large cavity size and are more susceptible to mechanical damage.

Handling in importing countries: Papayas should be stored at 10oC to 12oC. Temperatures below this range will cause chilling injuries and rapid deterioration in fruit quality. To induce ripening, handlers should store papayas at 18oC to 25oC and treat them with ethylene at 100 parts per million (0.01 percent) for 24 hours. Unripe papayas are sensitive to ethylene and will commence ripening if stored with ethylene-producing commodities. Similarly, ripe papayas produce ethylene and will cause deterioration in ethylene-sensitive crops.