الفهرس 
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Abstract
Handling and storage processes are considered the most important
factors affecting the quality of the agricultural products after harvesting. After
preliminarily surveying for the most effective problems facing the handling and
storage of the agricultural products, it was found that, under the currently used
system for oman storage in Egypt, the bulk of onions is stored in the field
where they are placed in piles covered with rice straw and kept under the
ambient conditions for 5 months. During the Summer period, the average
temperature is high (35°C) and the relative humidity is low (30%) while in the
rainy season, rhe temperature is around 21°C and the relative humidity is more
than 60 %. The dimensions of these piles vary from a farmer to another and
from one place to another. The total weight losses of onions for this method are
about 50 %, which are mostly due to moisture loss and deterioration by insects
and microorganisms. Moreover, the losses due to harvesting and handling of
onions before storage amount to 7.4 % of the total production (CAPMS of
A.R.E.,1980-1994).
In Egypt, the onion is one of the most important crops, not only for local
consumption but also for export, and is considered one of the main sources of
hard currency. The Egyptian onion is grown as winter crop in Middle and
Upper Egypt in August to September and it is harvested in January to
February. In Delta area, onion is grown as a summer crop in October to
November and harvested in May to June. It is grown also as an interplanted
crop for mature dry bulbs and green bunch in February to March, and
harvested in July (Morsy et al., 1959~Eweida et al., 1986~El Kafoury, 1986~
and EI-Sheekh et al., 1994). In 1993, the total cultivated area was 63302 ha
and the total production was 1150334 tonnes (18.17 ton.zha). Most Middle
and Upper Egypt onion production is devoted for export and all production of
Delta onion is used for domestic consumption (CAPMS of A.R.E., 1980-
1994). Although Egyptian exports represented 80.4 % of total African exports
in 1993, exports of Egyptian onions have decreased from 159000 ton in 1965
to 137560 tonnes in 1993 (FAa, 1976-1993) due to the decreased production
in the Middle and Upper Egypt and the increased local consumption. Also, the
delay in production, the unsuitable packages used for exports, and the
complicated operations in shipping are reasons for decreased exports (Saleh et
al., 1992).
For sound storage of onions, important factors such as cultivation
practices, harvesting and curing time, control of temperature and humidity in
the store, storage structure design, and application of sprout-inhibiting
chemicals play major roles. Onions as perishables have an optimum
temperature range for storage, above which, they respire at unacceptably high
rates and are more susceptible to ethylene and disease damage. According to
Robinson et al. (1981), Wang (1982) and Kader (1986), most horticultural
commodities respire at rates which double, triple, or even quadruple for every
10°C (18 OF) increase in temperature. On the other hand, temperature below
the optimum will result in freezing or chilling damage. The optimum conditions
to store onions are O°C temperature and 65-70% relative humidity (RH) with
adequate air circulation (Hardenburg et al., 1986~ and Smittle 1988). No
commercial application has been identified for varieties with long storage
potential for controlled atmospheres (CA). Onions are damaged by < 1% O2
and 10% C02. There is some commercial use ofCA (3% O2 and 5-7% CO2)
for sweet onion varieties (short storage potential). Losses in quantity and
quality occur in onion crops between harvest and consumption. The magnitude
of postharvest losses of onions are estimated to be 5 to 25 %in developed
countries and 20 to 50% in developing countries, depending upon the
commodity (Kader, 1985).
The main aim of this work was to evaluate the current Egyptian storage
system for onions and to develop an appropriate system for onion storage that
will minimize the losses, preserve the quality of onions and prolong the storage
life of onions in order to overcome the supply demand problem during the rest
of year and keep the onion prices stable through the whole year.