The increased worldwide trade in fresh fruits and vegetables arose from the importance of these commodities to the human diet. They bring to our daily diet variety, flavour and aesthetic appeal while they meet certain essential nutritional necessities. Furthermore, the nutritional importance of fruit and vegetables can be seen as an advantage since they offer a high concentration of vitamins and minerals with a low contribution of calories and fats.
Fruits and vegetables are very rich sources of vitamins particularly vitamin A, in the form of ß-carotene, the precursor of vitamin A and vitamin C.
For example, daily human requirements for vitamin C are about 50mg, and many commodities such as kiwifruit and pepper, contain this amount in less than 100g of tissue. However, nutritional value of fruits and vegetables can be greatly affected by the storage environment. In general, vitamin C degradation is very rapid after harvest, and increases as the storage time and temperature increases. For example, losses in vitamin C content of strawberries stored at 1°C ranges from 20 to 30% over 8 days, while strawberries stored at 10°C may lose from 30 to 50% of their initial vitamin C content. At 20°C losses are very high and strawberries may lose 55 to 70% of the initial vitamin C content in only 4 days.
Fruit is defined as the edible product of a plant or tree, consisting of the seed and the envelope, especially the latter when juicy and pulpy. Fruits are usually soft, fleshy, edible plant products and because of their high moisture content are relatively perishable in the freshly harvested state.
The vegetables exhibit a wide variety of plant structures. They can be grouped into three main categories: seeds and pods; bulbs, roots and tubers; flowers, buds, stems and leaves.
Like human beings, fruit and vegetables are ‘living’ structures as they continue to respire even when detached from the plant. Respiration (consumption of oxygen with release of carbon dioxide plus water vapour) is the major metabolic process that takes place in harvested produce or in any living plant product. It can be described as the breakdown of complex material normally present in the produce such as starch, sugars and organic acids into simpler compounds such as carbon dioxide and water. This process is associated with the production of energy (heat).
The respiration rate of a produce is an excellent indicator of the metabolic activity of the tissues and is therefore a useful guide to the potential storage life of the produce. As the temperature of the surrounding environment increases, the respiration rate of the product increases, while shelf-life decreases due to the loss of stored reserves. In general, the higher the respiration rate of a fruit or vegetable the more perishable the product is.
Based on their respiration and ethylene production patterns during maturation and ripening, fruits can be classified as climacteric or non-climacteric. Climacteric fruits show a large increase in carbon dioxide and ethylene production rates that are coincident with ripening; while non-climacteric fruits show no changes in their generally low carbon dioxide and ethylene production during ripening.
Classification of Some Fruits According to their Respiratory Behaviour During Ripening
Ethylene is a natural organic compound produced by plants that regulates growth, development and senescence. Climacteric and non-climacteric fruits may be further differentiated by their response to applied ethylene and by their pattern of ethylene production during ripening. All fruits produce small quantities of ethylene during development.
However, coincident with ripening, climacteric fruits produce much larger amounts of ethylene than non-climacteric fruits. There is no relationship between the ethylene production capacity of a given commodity and its perish-ability. However, preventing exposure of such commodities to ethylene decelerates their ‘death’ (end of shelf life).
Therefore, ethylene released by such commodities or exhaustion gases (generated by machinery such as fork-lifts, cigarette smoke or other fumes) may accumulate in a closed room and cause undesirable accelerated ripening. This is why mixed storage of high ethylene producers is not advisable when other highly sensitive produces are present.