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Storage and Post-harvest
reduce respiration and conserve moisture within the product. These will be described later below.
Vegetables Vegetables are derived from virtually all types of plant tissue and include underground organs such as swollen roots (e.g. carrots, Daucus carota) and swollen stem tubers (e.g. potatoes, Solarium tuberosum), and above ground parts such as leaf blades (e.g. spinach, Spinacia oleracea), axillary buds (e.g. Brussels sprouts, Brassica oleracea), swollen inflorescences (e.g. broccoli, Brassica oleracea and seeds (e.g. sweet corn, Zea mays). Vegetables also include some fleshy fruits such as tomatoes (Ly copersicon esculentum) and cucumbers (Cucumis sativus) and immature fruits such as peas (Pisum sativum) and bean pulses (Phaseolus spp.). The part of the plant that the vegetable develops from has important implications for its likely storage ability. The stage of development may also be critical in the maintenance of quality in the shorter or longer term. Vegetables such as lettuce (Lactuca sativa) and spinach, which are made up of young tissues, are respiring and transpiring actively and are likely to lose quality particularly rapidly; in commercial practice, immediate steps are taken to reduce the rate of metabolism and transpiration of the product. Practical measures for preserving the quality of vegetables (including those of a highly perishable nature) will be considered later. Certain types of vegetable are more suited to storage, particularly those that are biennial in nature; normally some kind of storage organ is formed in the first season, followed by flowering and seed formation in the second year. Although biennial vegetables are extremely varied morphologically they all cease growth in the autumn. The rate of metabolism (respiration rate) of their storage organs declines naturally which makes them adapted for long-term storage. Storage techniques have been developed to extend the natural dormant period of biennial vegetables and increase the period of their availability. Commercial storage of biennial vegetables in the UK includes winter white cabbage (Brassica oleracea), onion bulbs (Allium cepa) and potatoes.
Fruits The botanical definition of a fruit is a 'seed receptacle developed from an ovary' (see also Chapter 1); a consumer definition is more likely to concentrate on sensory qualities, the aromatic flavours and sweetness that distinguish a fruit from a vegetable. In nature the aromas and palatable nature of most fruits are important to ensure that seeds are consumed and dispersed by animals. The tissues (up to twelve types) that form various fruits are derived from different parts of the flower. Some examples from the temperate fruits that are common in gardens include strawberries (receptacle), apples (accessory tissue) and tomatoes (placental tissue). Ripening is a term reserved for fruits and relates to changes in colour, texture, flavour and aroma. The state of ripeness at the point of harvest has particular implications for producers and consumers alike. Generally fruits that are allowed to ripen on the plant achieve a higher sensory quality, but are more susceptible to damage during post-harvest handling and may have a reduced storage life. The biochemical changes associated with fruit ripening and the controlling mechanisms continue to attract much research attention. Understanding the ripening processes may in future show how ripening can be controlled more effectively, and so increase product availability and improve the eating quality and nutritional value of products to the consumer. Although fruit is important in a healthy diet, it is likely that many consumers eat fruit primarily for enjoyment. The perception of flavour is an important part of sensory quality, and it is vital that technologies to extend the period of availability of fruits do not result in an unacceptable loss of flavour quality. The flavour of fruits is derived from a complex mix of sugars, acids, phenolics and more specialised flavour compounds, including a wide range of volatile chemicals. Sugars (and acids) originate from photosynthesis and in some fruits such as apples and pears these sugars are converted to starch during fruit development. Fruits that accumulate carbohydrates such as starch are often picked at an immature stage and only achieve an acceptable flavour during subsequent ripening when starch is