The optimal storage conditions for papaya vary according to the maturity state in which they are harvested. If they are harvested when green or with a quarter of their surface of yellow colour, they must be stored at 13ºC. If they are partially mature (between ¼ and ½ of their surface of yellow colour), the temperature must be lowered at 10ºC. If they are mature (more than half of the skin of yellow colour) the optimal temperature is 7ºC. The optimal relative humidity in all the cases is 90-95%.

Papaya has a respond to the application of ethylene. If it is subject to an atmosphere with 100ppm of this gas, around 20 and 25ºC and with a humidity of 90-95% for 24-48 hours, maturation is faster and more uniform.

If modified atmospheres are used, maturation may be delayed, improving the firmness of the fruit. The optimal conditions are 3-5% of oxygen and 5-8% of carbon dioxide. Under these conditions, at a temperature of 13ºC they may be stored up to 5 weeks, whereas in normal atmosphere the maximum is 4 weeks.

Heat treatments are used to control insect attacks. There are several methods:

Hot water: 30 minutes at 42ºC followed by 20 minutes at 49ºC.
Water steam: temperatures of 44.4ºC are reached, kept for more than 8 hours.
Hot air: in two hours intervals, papayas are put under temperatures of 43ºC, 45ºC, 46.5º and finally at 49ºC.

Papayas may undergo different problems like physiological alterations during their storage, caused by an excess of cold or heat. They may also be affected by diseases like Colletrotichum gloesporioides, Poma caricae-papayae, Phomopsis caricae-papayae and Phytophthora nicotianae.

Among the various problems affecting papayas during their storage we find the mechanical damages and diverse physiological alterations and diseases.

The skin of the papaya is thin and offers little protection; it is easily damaged by rubbing, hits or cuts.

Among the physiological alterations there are:

Skin abrasion: characterized by green areas when the fruit matures; they burst and accelerate the loss of water.

Chilling injuries: they cause the appearance of ‘dimples’ in the fruit, spots, unequal maturation, skin scald and hard areas where the pulp becomes watery. Green papayas are more susceptible than the mature ones.

Heat injuries: if papayas are put under temperatures over 30ºC for more than 10 days, it causes alterations like irregular maturation and excessive softening of the fruit. These damages are diminished with fast-cooling at 13ºC after the heat treatment.

Among the diseases affecting papaya during storage, there are the following ones:

Antracnosis: originated by the fungus Colletrotichum gloesporioides, mainly causing great postharvest losses. It generates brown and superficial small injuries, that may measure 2.5cm or more.

Poma caricae-papayae is a fungus affecting the fruit’s peduncle, turning it brown or black.

Phomopsis caricae-papayae affects the fruit turning the skin into a black colour and softening it.

Phytophthora nicotianae is a fungus that causes watery areas in the fruit that are afterwards covered by a white down.

The strategies to control these diseases are: careful handling in order to reduce mechanical damages, cooling the produce as soon as possible, application of fungicides like tiabendazol and put the fruits under hot water at 49ºC for 20 minutes.