11.5.3 Ripening triggers

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Ethylene is both a promoter and a product of fruit ripening, and an accelerant of senescence in vegetables and cut flowers. Ethylene hastens ripening in a number of fruit (Tucker 1993), and despite contrasts in endogenous ethylene production most fruits nevertheless respond to exogenous ethylene as an external ripening trigger.

In climacteric fruits, ethylene exposure brings about an autocatalytic production of ethylene, and ripening proceeds rapidly, continuing even when exogenous ethylene has been removed. In non-climacteric fruits, when ethylene is present loss of chlorophyll proceeds more rapidly and respiration increases.

Taking kiwifruit as a test case, ethylene promotes ripening, but if exposure to ethylene is insufficient, or fruit are too immature, then removal of ethylene results in non-climacteric behaviour. Ethylene as a ripening trigger is used commercially with banana, avocado and early-season kiwifruit to ensure that fruit are at optimum ripeness when eaten. Conversely if kiwifruit are to be stored a long time, then ambient ethylene must be removed (usually by scrubbing this gas from coolstore environments).