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Peach, Prunus persica / Rosaceae
Postharvest Atmosphere Management
Peach
Peaches must be put under a precooling treatment for their correct conservation, and later on put in storage rooms at a temperature around 0ºC.

Preecooling is essential after the harvesting. This must take place within the first 12 hours of reception, working under 95% relative humidity conditions. The most advisable method of precooling is hydro-cooling, because it favours the fruit’s turgidity when the heat is released.

It is very important not to exceed the storage capacity of 150 Kg/m3. There must also be a continuous and periodic renovation of the environment in order to avoid ethylene. The application of ethylene to the fruit harvested in the suitable degree of maturity will only lead to a greater uniform maturity, without accelerating the rate of maturation. The main benefits obtained from the application of controlled atmospheres are the preservation of turgidity and the change from a green fruit to a mature one. Thus, for example, the conditions of controlled atmosphere for peaches are 6% of O2 and 17% of CO2.

The maximum self life is obtained when the fruit is stored approximately at 0ºC and varies from 1 to 7 weeks for nectarines and from 1 to 5 weeks for peaches. Given that internal degradation is the greater limiter for self life, the postharvest life is significantly less when the fruit is stored at 5ºC.

The storage after harvesting is determining for the fruit’s self life, but the production practices have also a very important role. Thus, for example, the small fruit that has grown in the external part of the crown has a longer self life than the greater size one that has grown in an internal position.
Postharvest Problems
The peaches may have brown internal deteriorations due to the cold conditions or external black deteriorations that reduce the quality of the fruit.

There are several fungi that also affect the external aspect of the peach, producing rots.

Peaches, throughout their conservation, may suffer different physiological deteriorations or physiological disorders and diseases.
The most remarkable physiological disorders are:

- Internal Deterioration or damage by cold: characterized by an internal browning of the fruit pulp, tissues’ mealiness, red iking in the fruit pulp, incapacity of maturation and flavour loss. These symptoms are usually detected by the consumer since they develop during the maturation period, after cold storage. The fruit with more susceptibility to this problem is the one stored within a range of temperatures of 2,2 to 7,6 ºC.

- Black Colouring (Inking): it is a cosmetic problem that affects only the skin. It is characterized by black or coffee dots or grooves. The symptoms usually appear within 24-48 h after the harvest. The black colouring is due to the damage by rubbing. This takes place during the stages of postharvest handling, although it is more usual that they appear in the operations of harvest and transport. The recommendations to reduce black colouring are to handle the fruit carefully and to avoid applications of nutrients on the leaves during the last 15 days before the harvest, as well as to follow the guidelines of the deficiency period to apply fungicides in preharvest.

Concerning the diseases, the most outstanding are:

- Brown rot: caused by the Monilinia fructicola fungus, it is the most important postharvest disease. It is characterized by a dark brown humid spot in the surface of the fruit, that quickly develops into a humid and soft rot in the whole fruit. The injuries are later covered with white mycellium. A bitter scent similar to vinegar goes along with rotting. The infection begins in the flowering; the rot may take place before the harvest but it often occurs in postharvest. As preventive control measures it is recommended to clean the orchard to diminish infection sources, the application of fungicides in the preharvest period and the immediate cooling of the fruit after the harvest.

- Gray Mould: caused by Botrytis cinerea. It is characterized by the appearance of a cottony grayish mould. It can be of great impact during the wet season of spring. It usually appears once the consumer has stored it at home, in the case that the fruit has been contaminated during harvest or due to handling damages.

- Rhizopus rot: caused by Rhizopus stolonifer, it is found in mature or almost mature fruits maintained at 20-25ºC. The infected tissue is brown but nonwatery and the rotten solid part can be easily removed. It is possible to fight against it by cooling the fruit or maintaining it below 5ºC.
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