Saturday, December 13, 2008

HOW DO FRUITS RIPEN?

Ripening of fruits is associated with the process of senescence or aging in plants. It involves change in colour, texture, flavour, sugar content and acidity, and is influenced by the ripening hormone ethylene. As ripening begins there is a climacteric increase in respiration, which is followed by increased ethylene production. It triggers a series of biochemical changes such as lateral growth, loosening of cell walls resulting in more intercellular spaces, conversion of starch and organic acids into sugars, hydrolysis of stored materials, softening by enzymatic changes of pectin substances, decrease in chlorophyll content with corresponding increase in anthocyanin pigments and emission of characteristic volatile oils. It is well known that ethylene production is increased more than 100-fold during climate rise. Colour changes occur due to synthesis of carotenoids and phenolic compounds like anthocyanins. Changes in texture occur by limited degradation of cell walls followed by an increase in poly-galaturonase and pectin-esterase activity. In banana and apple, the enzyme phosphorylase and in mangoes, amylase, break the starch into glucose and sucrose leading to their sweet taste. Volatile compounds such as ethyl-2-methyl butrate elicit a sweet smell. He adds, acidity of fruits is due to the presence of malic acid, citric acid, and malic acid and tartaric acid. Ripening is a pre-requisite for the development of embryos after fertilization and for better dispersal of seeds for survival.

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