Fruits Vegetables
es en ca
Date, Phoenix dactylifera / Palmae
Postharvest Atmosphere Management
The optimal temperature for storage during 6 or 12 months is 0ºC, depending on the variety (semidry dates like "Deglet Noor" and Halawi, have a longer period of life than other fresh dates like "Medjool’ and " Bardhi’).

At -18ºC (0ºF) the period of storage extends. The freezing point is –15.7ºC (3.7ºF).

The optimal relative moisture oscillates around 70-75%.

Cooling is the technique used to preserve soft dates varieties for two weeks. In order to avoid dehydration, dry dates must be stored in cool and dry places, protected from the sun and air. Under these conditions the period of storage lasts for several months and even a year.

The fresh produce consumed at present are put under preservation processes immediately after the harvest, ultra-frozen and later on defrosted just before they are put into sale. Dates which have undergone this treatment are barely damaged because they contain very little fluid and a lot of sugar (up to 70% of the total is inverted sugar).

Ripe dates are hardly influenced by ethylene but they can really absorb the aroma of some other produce. Dates must not be stored next to garlic, onions and potatoes.

Storage under controlled atmosphere with nitrogen (excluding oxygen) diminishes rottings of the dates and prevents the infections caused by insects.

For further information consult the Web page of the University of Davis ( http://postharvest.ucdavis.edu )
The same environmental conditions for conservation are recommended for the transport and distribution stages. These are: temperature around 0ºC for preservation between 6 and 12 months and relative moisture between 70 and 75%.
Postharvest Problems
After the harvesting some problems may arise caused by rotting, the fruit turning sour, the sugar crystallization on the surface and damages caused by pathogens.

Dates undergo enzymatic and non-enzymatic processes that increase with humidity and high temperatures. The enzymatic processes can be inhibited by means of low concentrations of oxygen. It can be that the enzymatic processes release fluids that favour the proliferation of pathogens.

The fermentation that makes dates turn sour takes place in fruit with 25% of moisture content.

Sugar crystallization
Sugar crystallization on the fruit’s skin and flesh occurs in some varieties of dates. It does not usually influence the taste but it affects the texture and appearance of the fruit. It is recommended to maintain low temperatures of storage in order to avoid this disorder.

This type of crystallization usually takes place in varieties in which the glucose and fructose are the chief sugar elements.

Damages caused by pathogens
Most of the damages caused by microbes are due to yeasts (most of them important), mould and bacteria. The yeast species Zygosaccharomyces are quite tolerant to high sugar contents than other found in dates. Dates infected by yeast give off an alcoholic smell (similar to fermentation). The bacterium Acetobacter is capable to turn alcohol into acetic acid (vinegar). Fungi (Aspergillus, Alternaria and Penicillum spp) may develop in dates with high levels of moisture, specially when they undergo humid or rainy periods.
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