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Pear, Pyrus cummunis / Rosaceae
Postharvest Atmosphere Management
Pear
The summer varieties may last between 2 and 10 weeks if they are conserved at 0 or 1ºC, whereas the autumn-winter varieties last between 3 and 7 months in the same condition. The pear conserved in storage room must be kept for several days at 20ºC before it is marketed, and must arrive firm at the consumer. They usually puts a drop of wax in the peduncle to avoid the penetration of fungi or bacteria through the cut, causing the rotting of the fruit.

In the case of the varieties Bosc, Comice and Anjou, the optimal temperature varies from -1 to 0ºC; the freezing temperatures are between -1,5 and -2ºC. The optimal humidity is of 90-95%.

The chilling helps to the uniformity of maturation, causing all of the stored pears to mature almost at the same time. The treatment of pears with 10 ppm of ethylene for 1 or 2 days may replace the cooling (4 to 8 weeks at -1 and 0ºC) for a uniform maturation. The optimal conditions of maturation are 15-22ºC (the higher the temperature, the faster the maturation takes place), and 90-95% of relative humidity. CO2 must be kept below 1%.

In the case of controlled atmospheres, the optimal rank is 1-2% of O2 and 0-1% of CO2. The winter varieties may be stored thus at temperatures of -1ºC for more than 4 months, according to the varieties. Oxygen levels below 1% and/or carbon dioxide levels over 1% for more than two weeks bring about physiological disorders. The greater damages take place with very low levels of O2, high levels of CO2, high temperatures and storage for a certain length of time.

As an example, the optimal conservation of the ‘Blanquilla’ pear is between -0,5 and 0ºC, with a relative humidity of 92% and a level of ethylene of 2 ppm. In controlled atmosphere, oxygen must be kept at 2.5% and carbon dioxide at 1,5%.

Concerning the nashi, some varieties are kept up to 6 months at temperatures between 0 and 1ºC and 90% of relative humidity. However, the conservation depends on the maturation stage of the fruit at the moment of harvesting. The conservation may last up to 2 months in controlled atmosphere.

Pre-cooling is recommended for a good conservation of pears. The aim of this technique is to remove the high temperature of the fruit when it reaches the fruit packing station. The heart of the fruit must be cooled down until it reaches 0-1ºC in the first 24 hours.
Distribution
In general, pears must be transported at temperatures near 0ºC, always taking into account the fruit’s freezing point. In this way, the damages concerning rots and deterioration of the fruit diminish. The moisture levels must be high, around 95-100%, in order to avoid drying.
Postharvest Problems
Pears may show various physiological alterations or diseases during their conservation. Among the physiological problems there are brown heart, dehydration, internal breakdown and scald. Among the diseases we find blue mould and gray mould.

Brown heart: it is perceived when a pear is cut in half, showing a brown colour around the seeds, along with a dense and shining liquid that surrounds the seeds. It occurs when the CO2 in the storage room is excessive.

Dehydration: it brings about the fruit’s loss of weight.

Internal breakdown: the symptoms are a general softening of the fruit, decomposition of the pulp from the heart, and the appearance of a translucent beige colour spot. This physiological alteration is accelerated by a delayed harvesting.

Scald: at the beginning, the fruit looses its colour, and afterwards takes place a browning of the skin of irregular shape and variable colour. This alteration is due to multiple causes, such as an early harvest, a delayed cooling, lack of ventilation during conservation and high oxygen levels.

Blue mould: caused by the fungus Penicillium expansum, that brings about blurred spots of a pale brown colour, causing the rot. The affected zone is covered with a white powder that turns into a bluish green colouring.

Gray mould: caused by the fungus Botrytis cinerea. This fungus gives birth to a rot covered with a gray filter. It usually attacks the peduncle.

Rhizopus: it resembles mould. The fruit attacked by this fungus gives off a characteristic fermentation smell.
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