Ripening is a process in fruits that causes them to become more palatable. In general, a fruit becomes sweeter, less green, and softer as it ripens. Even though the acidity of fruit increases as it ripens, the higher acidity level is not reflected in its flavor, which can lead to the misunderstanding that the riper the fruit the sweeter. This curious fact is attributed to the Brix-Acid Ratio.
Ripening agents speed up the ripening process.
They allow many fruits to be picked prior to full ripening, which is useful, since ripened fruits do not ship well. For example, bananas are picked when green and artificially ripened after shipment by being gassed with ethylene. A similar method used in parts of Asia was to cover a bed of slightly green-harvested mango and a few small open containers of clumps of calcium carbide with a plastic covering. The moisture in the air reacted with the calcium carbide to release the gas acetylene, which has the same effect as ethylene. Ethylene is not emitted by the plant naturally, and cannot activate the ripening of nearby fruits, rather, it used as a hormone within the plant.
Calcium carbide is used for ripening the fruit artificially in some countries. Industrial-grade calcium carbide may contain traces of arsenic and phosphorus, and, thus, use of this chemical for this purpose is illegal in most countries. Calcium carbide, once dissolved in water, produces acetylene, which acts as an artificial ripening agent. Acetylene is believed to affect the nervous system by reducing oxygen supply to brain; however, it has been shown that, in practice, acetylene is not sufficiently reactive to affect consumers.
Catalytic Generators are used to produce ethylene gas, simply and safely. Ethylene sensors can be used to precisely control the amount of gas.
Covered fruit ripening bowls are commercially available to increase fruit ripening. The manufacturers claim the bowls increase ethylene and carbon dioxide gasses around the fruit which promote ripening.
Climacteric fruits are able to continue ripening after being picked, a process accelerated by ethylene gas. Non-climacteric fruits can ripen only on the plant and, thus, suffer from short shelf-lives.
Banana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red.
Although fruit of wild species (Musa balbisiana) have large, hard seeds, virtually all culinary bananas are "seedless", have only tiny seeds. Bananas are classified either as dessert bananas (meaning they are yellow and fully ripe when eaten) or as green cooking bananas.
During the ripening process, bananas produce a plant hormone called ethylene, which indirectly affects the flavor. Among other things, ethylene stimulates the formation of amylase, an enzyme that breaks down starch into sugar, influencing the taste of bananas. The greener, less ripe bananas contain higher levels of starch and, consequently, have a "starchier" taste. On the other hand, yellow bananas taste sweeter due to higher sugar concentrations. Furthermore, ethylene signals the production of pectinase, an enzyme which breaks down the pectin between the cells of the banana, causing the banana to soften as it ripens.
Export bananas are picked green, and ripen in special rooms upon arrival in the destination country. These rooms are air-tight and filled with ethylene gas to induce ripening. The vivid yellow color normally associated with supermarket bananas is in fact a side effect of the artificial ripening process. Flavor and texture are also affected by ripening temperature. Bananas are refrigerated to between 13.5 and 15 °C (56 and 59 °F) during transport. At lower temperatures, ripening permanently stalls, and turns the bananas gray as cell walls break down. The skin of ripe bananas quickly blackens in the 4 °C (39 °F) environment of a domestic refrigerator, although the fruit inside remains unaffected.
A 2008 study reported that ripe bananas fluoresce when exposed to ultraviolet light. This property is attributed to the degradation of chlorophyll leading to the accumulation of a fluorescent product in the skin of the fruit. The chlorophyll breakdown product is stabilized by a propionate ester group. Banana-plant leaves also fluoresce in the same way. Green bananas do not fluoresce. The study suggested that this allows animals which can see light in the ultraviolet spectrum (tetrachromats and pentachromats) to more easily detect ripened bananas.
Bananas must be transported over long distances from the tropics to world markets. To obtain maximum shelf life, harvest comes before the fruit is mature. The fruit requires careful handling, rapid transport to ports, cooling, and refrigerated shipping. The goal is to prevent the bananas from producing their natural ripening agent, ethylene. This technology allows storage and transport for 3–4 weeks at 13 °C (55 °F). On arrival, bananas are held at about 17 °C (63 °F) and treated with a low concentration of ethylene. After a few days, the fruit begins to ripen and is distributed for final sale. Unripe bananas can not be held in home refrigerators because they suffer from the cold. Ripe bananas can be held for a few days at home. They can be stored indefinitely frozen, then eaten like an ice pop or cooked as a banana mush.
Ethylene is an anesthetic agent (in an 85% ethylene/15% oxygen ratio) and it can be used to hasten fruit ripening.
Ethylene serves as a hormone in plants. It acts at trace levels throughout the life of the plant by stimulating or regulating the ripening of fruit, the opening of flowers, and the abscission (or shedding) of leaves. Commercial ripening rooms use "catalytic generators", to make ethylene gas, from a liquid supply of ethanol. Typically, a gassing level of 500 ppm to 2,000 ppm is used, for 24 to 48 hours. Care must be taken to control carbon dioxide levels in ripening rooms when gassing, as high temperature ripening (68F) has been seen to produce CO2 levels of 10% in 24 hours.
Ethylene has been used in practice since the ancient Egyptians, who would gash figs in order to stimulate ripening (wounding stimulates ethylene production by plant tissues). The ancient Chinese would burn incense in closed rooms to enhance the ripening of pears. In 1864, it was discovered that gas leaks from street lights led to stunting of growth, twisting of plants, and abnormal thickening of stems. In 1901, a Russian scientist named Dimitry Neljubow showed that the active component was ethylene. Doubt discovered that ethylene stimulated abscission in 1917. It wasn't until 1934 that Gane reported that plants synthesize ethylene. In 1935, Crocker proposed that ethylene was the plant hormone responsible for fruit ripening as well as senescence of vegetative tissues.
See also: http://en.wikipedia.org/wiki/Ripening
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)