|Characteristics and fitness for container transport
Vegetables are edible plant parts, such as leaves, shoots, stalks, flowers, fruits, seeds, buds, roots, rhizomes (rootstocks), which are predominantly obtained from annual and herbaceous plants.
Vegetables, like fruit, can be classified in accordance with various criteria, but the following classification based on the part of the plant which is used is effective for transportation purposes and thus for container transport:
A comparison of the classification criteria for fruit and vegetables (see Table 13) shows that vegetables, like fruit, exhibit elevated, 2nd order biotic activity (BA 2) and a high water content (WCC 3); the water content of curly kale is 80% and that of cucumbers as much as 97%.
Table 13: Comparison of fruit and vegetables
Fruit and vegetables differ with regard to their constituents, with the sugar/acid content dominating in fruit and the starch content dominating in vegetables.
Examples of constituents are:
While chilling damage in fruit occurs far above freezing point, the transport temperatures for vegetables may be very close to freezing point.
Vegetables require specific temperature, humidity/moisture and ventilation conditions (SC VII) because respiration processes must be specifically controlled (dormancy temperatures), so requiring vigorous ventilation to supply oxygen and remove harmful gases, especially carbon dioxide.
Refrigerated containers with a fresh air supply and CA containers are the most suitable temperature-controlled transport.
Transport instructions and damage
Perforated plastic bags as the inner packaging in wet strength cartons are conventional for many kinds of vegetables. This type of packaging has proved particularly effective, for example, for sweet peppers, as shriveling and shrinkage of the thin skin rapidly impair quality. Sweet peppers are also transported in palletized cases, fruit crates, nets in food containers.
Carrots are usually washed and packaged in perforated plastic film bags and transported in fruit crates. Water vapor-impermeable film without perforations would cause the carrots to respire anaerobically, rapidly resulting in spoilage (soft surfaces, insipid flavor and hard black spots). Tomatoes are packaged in fruit trays made of wood, cardboard or plastic. It must be possible to provide potatoes and onions with proper ventilation and these products are thus often packaged in wide-meshed bags.
It is clear from Table 14 that transport temperatures for most kinds of vegetables are close to 0°C and even as low as -1°C. Berry-like types of vegetables, such as aubergines, egg-plants, cucumbers and tomatoes are an exception and have a transport temperature of 8 - 12°C. Vegetables are also somewhat more tolerant of temperature variations than is fruit (e.g. 0.5 - 2°C).
Table 14: Temperature and humidity/moisture conditions for fresh vegetable
storage during transport;
Chilling damage takes various forms, for example being manifested as dark, watery areas on the skin of sweet peppers. The skin becomes detached from the flesh and the inside of the sweet pepper may break down. In tomatoes, chilling damage results in softening of the fruit, associated with brown discoloration of the skin and loss of the ability to ripen. At < 3°C, potatoes become sweet, glassy and take on a watery, grey color. Carrots crack at the surface and the root becomes paler in color. At < 0°C, asparagus very rapidly freezes and dies. Onions and potatoes begin to sprout at > 4°C.
Transport temperatures for the frozen storage of vegetables are -18 - -20°C, as for fruit.
Table 14 shows that relative humidity is on average still higher (85 - 95%) than for fruit, in order to avoid flabbiness/shriveling and weight loss. Inner packaging in perforated film bags ensures retention of freshness.
When packing a container, fresh vegetables must be provided with particular protection from the action of wet weather (rain, snow) as softening and rot of e.g. potatoes, onions or carrots may otherwise occur. Consignments of new harvest onions are more susceptible to injury than warehoused onions due to their higher water content. Humidity/moisture results in self-heating, sprouting, root growth and decay of the bags, if they are made of jute. Wetting damage makes asparagus rubbery and mushy, which may often be observed if the ends of the asparagus bundles are packaged in paper sleeves to keep the cut surfaces fresh.
With the exception of tomatoes, vegetables are nonclimacteric. Tomatoes must not be packed in a container together with ethylene-sensitive kinds of fruit and vegetables, nor with cucumbers, which would age more rapidly. Potatoes are extremely sensitive to ethylene, especially to pomaceous fruit, such as apples. The latter cause premature sprouting of potatoes. Carrots are made bitter by the action of ethylene. Leaf vegetables, such as cabbage lettuce, are turned yellow by ethylene, the leaves develop brown spots and are finally lost.
A phytosanitary certificate must, on principle, be provided for container shipment. Potatoes, for example, are affected by quarantinable diseases, such as potato wart, bacterial ring rot, potato moth and powdery scab. The foliage (peduncle) of onions must have been twisted off (not cut off) as there is otherwise a risk of onion neck rot caused by the mold Botrytis allii. The commonest storage disease of tomatoes and washed carrots is grey mold rot, which is caused by the mold Botrytis cinerea. Carrots which have suffered mechanical damage are at particular risk from Fusarium spp. molds.
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