Fruits and vegetables are living parts of plants and contain 65 to 95 percent water. When water and nutrient reserves are depleted, rotting and death of these products occurs. Anything that increases the rate at which nutrients and water from a product’s reserves are used up increases the likelihood of losses. Acceleration of normal physiological development can be caused by high temperature, low atmospheric humidity, or physical injury. Such injuries often result from careless handling, causing internal bruising, skin tears, thus rapidly increasing water loss.
Respiration is a continuous process in plants and cannot be stopped without damage to either the growing plant or to harvested products. It uses stored starch or sugar and stops when the reserves of these elements are exhausted, leading to aging. Respiration depends on a good air supply. When the air supply is reduced, fermentation can replace respiration. Poor ventilation of the product also leads to the accumulation of carbon dioxide. The increase in carbon dioxide concentration quickly leads to losses.
Fresh produce continues to lose water after harvest. Water loss leads to shrinkage and weight loss. The rate at which water is lost varies with the product. Leafy vegetables lose water quickly because they have thin skins with many tomatoes. Potatoes, on the other hand, have a thick skin with few duckweeds. But whatever the product, to extend its life or shelf life, the rate of water loss must be minimal. The most important factor is the ratio of the surface area of the fruit or vegetable to its volume. The higher this ratio, the faster the water loss. The rate of loss is related to the difference between the water vapor pressure inside the product and in the air. Therefore, products must be stored in a humidity controlled atmosphere.
Diseases caused by fungi and bacteria cause losses, but viral diseases, which are very common in crops, are not a major problem after harvest. Deep decomposition renders infected products unusable. This is often the result of infection of produce in the field before harvest. Quality losses occur when the disease affects only the surface of the produce. Visible skin blemishes may lower the selling price, but do not make a fruit or vegetable inedible. Fungal and bacterial diseases are spread by microscopic spores, which spread through the air and soil or through decaying plant material. Infections can occur at any time after harvest. They often result from injuries caused during harvesting or handling.
Ripening occurs when a fruit is ripe. The ripening stage is followed by senescence and decay of the fruit. The “fruit” category also includes fruiting vegetables such as eggplant, peppers and tomatoes. Non-climacteric fruits only ripen when they remain attached to the mother plant. Their taste quality suffers if they are harvested before full ripeness, as their sugar and acid contents do not change afterwards. Examples are citrus fruits, grapes and pineapples. Early harvesting is often done for export shipments to minimize losses during transport, but the consequence of this practice is that the flavor suffers. Climacteric fruits are those that can be picked before the ripening stage has begun. These fruits include bananas, melons, papaya and tomatoes. In the marketing of commercial fruits the rate of ripening is artificially controlled, allowing careful planning of transportation and distribution.
Ethylene is a gas produced in most plant tissues that plays an important role in triggering the ripening process. It can be used commercially to ripen climacteric fruits. However, endogenous ethylene produced naturally by fruit can lead to storage losses. For example, ethylene destroys the green color of plants. Leafy vegetables may be damaged if stored with ripening fruit. Ethylene production is increased when fruit is injured or decaying and this can cause climacteric fruit to ripen prematurely during transport.
Source: wikipedia.org