WILL ONE BAD APPLE RUIN THEM ALL ?

You've heard that 'one bad apple spoils the whole barrel', right? It's true. Bruised, damaged, or overripe fruit gives off a hormone that accelerates the ripening of the other fruit -- ETHYLENE.

What is ETHYLENE ?

Ethylene (C2H4, also known as ethene) is a gaseous organic compound that is the simplest of the alkene chemical structures (alkenes contain a carbon-carbon double bond).  Ethylene is the most commercially produced organic compound in the world and is used in many industrial applications. 

Plant tissues communicate by means of hormones. Hormones are chemicals that are produced in one location that have an effect on cells in a different location. Ethylene is the hormone that will cause a wide range of effects in plants, such as fruit ripening, loss of chlorophyll, abortion of plant parts, stem shortening, abscission of plant parts, and epinasty (bending of stems) which  depending on the age of the plant and how sensitive the plant is to ethylene. Ethylene can be either good or bad, depending on what merchandise you work with. It is used in a positive manner in fruit ripening, for instance. It can also cause damage in crops. Examples of damage might include yellowing of vegetables, bud damage in dormant nursery stock, or abscission in ornamentals (leaves, flowers drop off). Most plant hormones are transported through the plant vascular system, but some, like ethylene, are released into the gaseous phase, or air.

                                         

Where does it come from?

Ethylene is produced and released by rapidly-growing plant tissues. It is released by the growing tips of roots, flowers, damaged tissue, and ripening fruit. The hormone has multiple effects on plants. One is fruit ripening. When fruit ripens, the starch in the fleshy part of the fruit is converted to sugar. The sweeter fruit is more attractive to animals, so they will eat it and disperse the seeds. Ethylene initiates the reaction in which the starch is converted into sugar.

Commercial Use of Ethylene to Ripen Fruit

Climacteric fruits are frequently harvested at a physiological stage that is considered ‘commercial maturity’, typically in a hard green but mature stage just before ripening has initiated.  Examples include bananas, mangoes, tomatoes and avocados.  This enables the fruit to be harvested, cooled, stored and transported significant distances to where it will be marketed and consumed.

Ripening can then be conducted under controlled conditions of temperature, relative humidity and ethylene to achieve uniform appearance and quality of ripe fruit.  Fruit is placed into specially constructed ripening rooms and brought to optimum ripening temperature and humidity.  Ethylene is then raised to a prescribed concentration using either a "catalytic generator" that makes ethylene gas from liquid ethanol or from commercially available gas supplies.  Forced-air cooling systems ensure that fruit are uniformly exposed to the room ethylene concentration.  When fruit are exposed to ethylene under these controlled conditions they will initiate their respiratory climacteric pattern and ripen at a relatively uniform rate.  Conditions and duration can be varied to suit customer specifications for stage of ripening and colour development.

However, concerns are periodically raised in mass media about fruit being ‘gassed’, implying that this confers some residual food safety risk from the ethylene gas and that the fruit has been somehow rendered ‘unnatural’.  The public should understand that the commercial use of ethylene for fruit ripening is at a low concentration and simply initiates the respiratory climacteric.  The ethylene used commercially has the same molecular structure.  By the time the ethylene-treated fruit reaches the consumer the climacteric may have started, there is no trace of applied ethylene gas, any ethylene emitted by the fruit is generated by the fruit itself and is of a much greater concentration.  Therefore, there are no food safety issues associated with the consumption of climacteric fruit.