[BojanaL]

Transformation of the fruit from green to fully mature, desirable for eating, is called ripening. Process is induced by gaseous plant hormone called ethylene. Its production is associated with outer temperature, surface wounds, and diseases. Ethylene triggers enzymatic activity that will convert complex polysaccharides (starch) to simple sugars, degrade chlorophyll and produce other pigments. Enzyme pectinase will degrade pectin and result in softer surface layer of the plant. Each fruit species demand certain weather conditions and climate to develop normally. During the past couple of years (thanks to improved shipping methods) fruit is traveling faster and people all over the globe can eat different types of fruit all year long. Ripened fruit can’t be safely transported because it is too soft and decay prone. Besides applying delay ripening methods, fruit is normally collected while still green. Artificial ripening (using different chemicals) will provide expected color and taste when fruit reach its final destination. Methods used in fruit ripening can provide fast and effective results but they are not necessarily 100% safe for humans. Also, if they are not administered properly, fruit might overripe and decay completely.

Calcium carbide is used as ripening agent in some countries. When combined with water, it turns in acetylene which induces fruit ripening. Calcium carbide can contain traces of arsenic and phosphorus that are known toxicants in humans. Mostly used ripening agent is ethylene. Specially designed facilities used for fruit ripening release previously determined amount of ethylene. Iodine is used to check ripening status of the fruit. Interaction between iodine and fruit sugar will indicate whether fruit is still green, in the ripening phase or fully ripe. Reaction between starch and iodine result in dark blue colored complex. Since starch turn in more simple sugar during ripening, green fruit will color dark when sprayed with iodine, while ripe fruit will produce bright color.

List of fruits that is collected while still green is long: bananas, papayas, mangos, tomatoes… are typical examples of fruit that will be harvested during “commercial maturity” stage and ripen prior being delivered to the desired location. Each species demand specific amount of ethylene to ripen properly. Although ethylene is safe artificial ripening agent, his storage and release could be a problem. Explosive accidents associated with tanks containing ethylene were reported in the past. Compressed gas is not just unsafe, but hard to accomplish and expensive to maintain. Scientists from the University of Queensland recently discovered another biological material that might offer solution for this issue. Starch derived material have crystalline structure and cavities that could safely encapsulate ethylene in couple of powder forms. Rise of temperature and humidity will induce ethylene release (from the powder complexes). This system is much cheaper and safer than previously used storage facilities and it could even be incorporated in the trucks that are delivering the fruit to the market. As a result, customers will be able to buy a fruit that have just ripened.

Another group of scientist (from the Massachusetts Institute of Technology) discovered the way to detect amount of ethylene using the newly developed nanotech device. Ethylene is small non-polar hard to detect molecule. Conventional methods applied in ethylene measurement are expensive. Newly developed device is portable, safe and easily produced. Sensor consists of two gold electrodes. Single walled carbon nanotubes and specially designed complex copper mixture lies in between electrodes. Bond between copper and nanotubes is very strong. When sensor is exposed to ethylene atmosphere, copper will bind ethylene and loosen its connection with nanotubes. Sensor is highly sensitive: electronic properties of the nanotube will register the slightest change in connectivity between copper mixture and nanotubes. Change in electronic resistance is proportional to the level of ethylene. Device was used to establish amount of ethylene released during ripening phase (amount of released ethylene is species specific) and to determine the peak of ripening for each species (when fruit ripen, it doesn’t demand ethylene anymore and it will slowly decrease its production). This little device could help prevent fruit from overripe and assist manufacturers while determining the proper amount of ethylene during ripening phase.

Newly applied method could greatly improve fruit ripening industry. Potential ethylene associated accidents could be prevented, timing associated with harvest and fruit ripening could be improved, and decay could be avoided.