Growth and Development of Horticultural Crops (1+1)

1. Changes with ripening

The general changes that occur during the process of ripening of fruits are,

1. Softening of fruit
2. Hydrolytic conversion of complex storage materials into simpler forms
3. Changes in pigments and flavours.
• Softening is an important change with the ripening of fruits. The major role played in this process is that of cell wall degrading enzymes, associated with hydrolysis of cell contents. As such pectolytic enzyme activities induces solubilization of pectic substances found in middle lamellae. The solubilization may occur through an increase in methylation of the galacturonic acid or through reduction in the size of a chain of polygalacturonoid or both.
• Hydrolytic changes in the fruit during ripening usually lead to the formation of sugars. Such changes show different rates in different fruits, e.g. banana ripens extremely fast, apple shows gradual ripening and citrus fruits show very slow changes.
• During ripening of fruits, some qualitative changes occur such as change in pigmentation, production of flavour and depletion of astringent substances.
• The changes in pigments in fruits are normally the loss of chlorophyll and the development of carotenoids. There may be changes in colour due to moderate loss of chlorophyll with little or no formation of carotenoids as in banana or due to complete formation of carotenoids, as in oranges. The pigment changes occur mainly in the chloroplasts with grana into chromoplasts with loosely dispersed thylakoid membranes. Electron microscopic studies have revealed that new thylakoid membranes are synthesized in the conversion. Chlorophyll is lost due to chlorophyllase activities. The newly developed pigments may be carotenes as in papaya or anthocyanins as is strawberry and these are synthesized in the presence of sunlight and with the involvement of phytochrome.
• Very little work has been done on development of flavour substances. In apples, numerous volatile esters, aldehydes, ketones etc. have been identified. The loss of astringent materials such as phenolics is commonly found in pomaceous fruits.