Lemon

Since lemons are citrus fruit having a juicy/aromatic flesh with a high acid content, they are primarily used for their juice and for seasoning. The flesh and juice are used to make lemonade, soft drinks, jams and the like, while the highly fragrant lemon oil is extracted from the peel in the countries of cultivation.

Figure
(Click on the Figure to enlarge it.)
Figure 1


Countries of origin
This Table shows only a selection of the most important countries of origin and should not be thought of as exhaustive.

Europe
Spain, Italy, Turkey, Cyprus

Africa
South Africa, North Africa, Egypt

Asia
Israel, India

America
Chile, Uruguay, Argentina, USA, Brazil, Mexico

Australia
 

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Packaging
Lemons are transported in boxes and cartons.

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Transport
Symbols
General cargo
Temperature-controlled


Means of transport
Ship, aircraft, truck, railroad

Container transport
Refrigerated container
with fresh air supply or controlled atmosphere.

Cargo handling
Because of its impact- and pressure-sensitivity, the fruit has to be handled with appropriate care.
The required refrigeration temperature must always be maintained, even during cargo handling.
In damp weather (rain, snow), the cargo must be protected from moisture, as there is otherwise a risk of premature spoilage.

Stowage factor


1.71 m3/t (cartons on disposable pallet) [1]


2.55 - 2.80 m3/t (boxes and cartons) [14]


Stowage space requirements
Cool, dry, good ventilation

Segregation
Fiber rope, thin fiber nets, wooden dunnage

Cargo securing
Because of its considerable impact- and pressure-sensitivity, packages of this cargo must be secured in such a way that they are prevented from damaging each other. Spaces between packages or pallets must be filled, to prevent slippage or tipping. By selecting the correct packaging size or cargo unit (area module or area module multiple), holds can be tightly loaded (without spaces).

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Risk factors and loss prevention
RF Temperature
Lemons require particular temperature, humidity/moisture and ventilation conditions (SC VII) (storage climate conditions).
A written cooling order must be obtained from the consignor before loading is begun. This order must always be complied with during the entire transport chain.
The following Tables merely constitute an estimate of appropriate temperature ranges. Temperatures may deviate from these values, depending on the particular transport conditions.

Designation
Temperature range
Source

Travel temperature
10 - 11°C
[1]

10 - 13°C
[2]

12 - 14°C
[5]

10 - 12°C
[6]

The cargo and holds/containers should be precooled prior to loading.
Depending upon the species and variety, all citrus fruits are highly cold-sensitive. Grapefruit, lemons and limes are more susceptible to chilling damage than are oranges and mandarins, and late-ripening varieties are more temperature-sensitive than early varieties. While oranges can withstand temperatures of 5°C, more temperature-sensitive types should never be shipped below 10°C. Green citrus fruits require higher transport temperatures than do yellow; the higher is the acid content of the fruit, the greater is its cold-sensitivity.
Chilling damage is manifested in citrus fruits in particular by spots on the peel (brown dots on the peel), accompanied by a bitter taste and unpleasant odor, rot and cell wall collapse. The glossiness of the peel is lost and the albedo layer (inner layer of the peel), which is normally white, turns a dark color. When the fruit is divided up, the segments, which have a low juice content, break up and the whole fruit is glassy and soft. The severity of the chilling damage is determined not only by the extent to which the temperature has fallen beneath the limit, but also by the length of exposure to this temperature. Chilling damage does not generally occur in cold stores, but instead prior to cooling or after leaving the cold stores.
Excessively rapid warming of refrigerated fruit results in condensation and spoilage.
During loading, pulp temperature measurements must be performed continually. The pulp temperature must never be < 4°C or > 25 - 30°C as storage life and appearance are impaired outside this range. Fruits punctured for pulp temperature measurement must be discarded as they would rapidly spoil and infect the other fruit. The measurements must be recorded.

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RF Humidity/Moisture
Lemons require particular temperature, humidity/moisture and ventilation conditions (SC VII) (storage climate conditions).

Designation
Humidity/water content
Source

Relative humidity
80 - 90%
[1]

85 - 90%
[2]

85 - 90%
[5]

85 - 90%
[39]

Water content
approx. 90%
[1]

Maximum equilibrium moisture content
85%
[1]

It is essential to protect lemons from moisture (seawater, rain, condensation, snow) as moisture in particular promotes green and blue mold and black rot.
In general, due to the high water content of lemons of approx. 90%, a relative humidity of 85 - 90% is required. Only lemons, oranges and mandarins with a dark green peel color are able to withstand a relative humidity of 82 - 85%.

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RF Ventilation
Lemons require particular temperature, humidity/moisture and ventilation conditions (SC VII) (storage climate conditions).
Recommended ventilation conditions: circulating air, 40 - 60 circulations/hour with continuous supply of fresh air
The addition of fresh air is extremely important as citrus fruit can start to ferment within a few hours due to anaerobic respiration (resulting in total loss of the fruit). If ventilation is inadequate, storage damage may occur, taking the form of a bitter flavor and peel scab.

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RF Biotic activity
Lemons display 2nd order
biotic activity.
They are living organs in which respiration processes predominate, because their supply of new nutrients has been cut off by separation from the parent plant.
Care of the cargo during the voyage must be aimed at controlling respiration processes (release of CO2, water vapor, ethylene and heat) in such a way that the cargo is at the desired stage of ripeness on reaching its destination. Inadequate ventilation may result in fermentation and rotting of the cargo as a result of increased CO2 levels and inadequate supply of atmospheric oxygen (see Ventilation).

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RF Gases

CO2 evolution
at 10°C: 12.5 mg/kg*h [1]


Upper limit of permissible CO2 content
0.1 vol.% [1] < 0.5 vol.% [39]


Ethylene evolution
 


Active behavior
The rate of ethylene production is very low, being below 0.1 µl/kg*h [16].


Passive behavior
Lemons are moderately sensitive to ethylene [16] and should thus not be stored with goods having an elevated ethylene production rate (allelopathy).

In fresh fruit, metabolic processes continue even after harvesting. The fruit absorbs oxygen (O2) and excretes varying amounts of carbon dioxide (CO2) and ethylene (C2H4) as well as aromatic compounds during the conversion of starch into sugar (ripening process).
Levels of respiratory gases which promote ripening, such as ethylene as well as carbon dioxide, should be kept as low as possible. If ventilation is inadequate, storage damage, such as a bitter flavor and peel scab, may occur. The supply of fresh air must thus be constant in order to dissipate these gases.

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RF Self-heating / Spontaneous combustion
No risk.

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RF Odor


Active behavior
Lemons have a strong, pleasant odor. Due to their high content of highly volatile essential oils (formic acid, acetic acid, ethanal, ethylene and the odor substance limonene), citrus fruits are in general a highly odor-contaminating cargo and must thus not be stowed or stored together with fruit, vegetables and other odor-sensitive foodstuffs.


Passive behavior
Lemons are highly odor-sensitive.


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RF Contamination


Active behavior
Lemons do not cause contamination


Passive behavior
Lemons are sensitive to contamination by dust, dirt, fats and oils. The holds or containers must accordingly be clean and in a thoroughly hygienic condition before loading.


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RF Mechanical influences
Lemons are highly impact- and pressure-sensitive. Spoilage due to mold and rot occurs in particular when the peel of the fruit is injured. Injury to peel occurs in the event of careless harvesting and due to incorrect handling of packages. Such injury may also be a sign of excessively low temperatures or incorrect use of postharvest phytosanitary agents.
Attention must be paid to the level of filling of cartons in order to avoid damage: they should be filled no higher than the top as overfilling will inevitably result in pressure damage, and thus premature spoilage, when the cartons are stacked. Bruises become soft and the squashed peel looks like "goose-pimples". The aroma of the fruit is also lost and the flavor becomes bitter and unpleasant.

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RF Toxicity / Hazards to health
If ventilation has been inadequate (frost) or has failed owing to a defect, life-threatening CO2 concentrations or O2 shortages may arise. Therefore, before anybody enters the hold, it must be ventilated and a gas measurement carried out. The TLV for CO2 concentration is 0.49 vol.%.

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RF Shrinkage/Shortage
The normal weight loss due to a reduction in the moisture content of the product is approx. 1 - 2% [1].

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RF Insect infestation / Diseases

Blue mold rot or storage rot is the most feared storage disease of citrus fruits and is caused by two species of mold: green mold (Penicillium digitatum), which is of an olive-green color, and blue mold (Penicillium italicum), which is of a blue-green color. Lemons are primarily attacked by green mold. The fungal spores mainly penetrate through small injuries and initially form white, circular spots of fungal growth, which are subsequently covered from the center outwards with a green or blue-green sporulating layer. The peel becomes spongy, the pulp soft - a typical instance of wet rot. Development is optimal at 20 - 27°C; growth still flourishes at 10°C and comes to a standstill only at 4°C. Blue mold is transferred from fruit to fruit by contact.
Seawater, rain and condensation water promote green and blue mold growth.

Figure 2
Figure 3
Figure 4

Black rot (beginning at flower end) and stem-end rot (beginning at stem-end) are forms of dry rot which may occur as early as during harvest. Moisture promotes blue mold rot and black rot.
The Mediterranean fruit fly (Ceratitis capitata), a quarantine pest, in particular attacks thin-peeled citrus varieties, especially oranges and mandarins. The 8 mm long maggots of this boring fly in particular attack ripening and ripe fruit, causing rotting. Complete destruction of affected fruit and the use of contact insecticides during the flight time are the most effective methods of control. Countries apply strict quarantine measures to prevent introduction of this pest. Import of affected fruit is prohibited. Since these pests have many different food sources, they can find food throughout the year in the Mediterranean region; in January mandarins are attacked, from February to May early to late oranges, in the summer peaches, apricots and pomaceous fruit and, at the beginning of winter, back to mandarins. Externally visible signs of attack are sunken, soft, black puncture marks and, subsequently, brownish discoloration of the peel.
The quarantine regulations of the country of destination must be complied with and a phytosanitary certificate may have to be enclosed with the shipping documents. Information may be obtained from the phytosanitary authorities of the countries concerned.

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Lemon juice, rind, and zest are used in a wide variety of foods and drinks. Lemon juice is used to make lemonade, soft drinks, and cocktails. It is used in marinades for fish, where its acid neutralizes amines in fish by converting them into nonvolatile ammonium salts, and meat, where the acid partially hydrolyzes tough collagen fibers, tenderizing the meat, but the low pH denatures the proteins, causing them to dry out when cooked. Lemon juice is frequently used in the United Kingdom to add to pancakes, especially on Shrove Tuesday.
Lemon juice is also used as a short-term preservative on certain foods that tend to oxidize and turn brown after being sliced (enzymatic browning), such as apples, bananas, and avocados, where its acid denatures the enzymes.
Lemon juice and rind are used to make marmalade, lemon curd and lemon liqueur. Lemon slices and lemon rind are used as a garnish for food and drinks. Lemon zest, the grated outer rind of the fruit, is used to add flavor to baked goods, puddings, rice, and other dishes.
The leaves of the lemon tree are used to make a tea and for preparing cooked meats and seafoods.

They can be stored for up to 6 months under the right conditions.