Senescence or biological aging of plants is associated with the ripening of fruits. It is influenced by the hormone ethylene and involves changes in acidity, color, flavor, texture and content. The production of ethylene increases nearly a hundred times.
When the ripening of a fruit begins, it involves a climacteric change ( a stage of fruit ripening associated with the production of ethylene and increased cell respiration). It sets off a series of biological changes such as lateral growth and loosening of cell walls. Fruits such as bananas, melons, apples, apricots and tomatoes. There are other fruits that are non-climacteric such as citrus, grapes and strawberries. These non-climacteric fruits do not require the production of additional ethylene nor do they have respiration bursts.
Color changes are due to the synthesis of carotenoids (organic pigments) and result in yellow or red color. Other compounds such as anthocyanins that give a fruit a red, blue or purple color depending on it pH value.
Textural changes are due to the limited degradation of cell walls and the activity of enzymes such as polygalacturonase and pectinesterase which plays an important role in the ripening of fruits.
Acidity in plants are due to the presence of citric acid (gooseberry, peaches and tomatoes), malic acid (plum, cherry, banana, apricot and apple) and both of these acids in grapes.
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