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This lemon will turn yellow as it ripens.

Ripe lemons.

Lemon in the process of ripening

Ripening is a process in fruits that causes them to become more edible. In general, a fruit becomes sweeter, less green, and softer as it ripens. However the acidity as well as sweetness rises during ripening, but the fruit still tastes sweeter regardless. The reason for this is the Brix-Acid Ratio.

The life stages of a plant are influenced by plant hormones. An organic compound involved with ripening is ethylene, a gas created by plants from the amino acid methionine. Ethylene increases the intracellular levels of certain enzymes in fruit and fresh-cut products, which include:

• Amylase, which hydrolyzes starch to produce simple sugars, and
• Pectinase, which hydrolyzes pectin, a substance that keeps fruit hard.

Other enzymes break down the green pigment chlorophyll, which is replaced by blue, yellow, or red pigments.

Hormone levels in fruit are often connected to pollination. If too few seeds in a multiseeded fruit are formed (by fertilization of the ovules), the flesh of the fruit may not develop in some areas, and as a consequence ripening will be retarded or prevented. Fruit growers increasingly monitor seed ratios in developing and/or mature fruit and adjust pollination management accordingly.

Many fruits are picked prior to full ripening because 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 apparently has the same effect as ethylene.

Climacteric fruits are able to continue ripening after being picked, a process accelerated by ethylene gas. Non-climacteric fruits can only ripen on the plant and thus typically suffer from short shelf-lives.

Some fruits, such as Hachiya persimmons, are eaten only after bletting, the fermenting process of decay after severe ripening.

SmartFresh is a technology useful to maintain fresh-picked quality of whole fruits and vegetables. 1-Methylcyclopropene (1-MCP 0.14%) works with the ripening process to dramatically slow down ethylene production and prevent over-ripening and problems associated with aging.

Iodine (I) can be used to check if the fruit is ripening or rotting by showing whether starch in the fruit has turned into sugar. For example, in an apple that has rotted (not bruised, just rotted) a drop of iodine on a slightly rotten part (not skin) will turn a dark blue or black color if there is starch there. If it stays yellow, then most of the starch did turn into sugar.

Artificial ripening

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 acetylene¹ which is the essential gas for ripening process. Acetylene is believed to affect the nervous system by reducing oxygen supply to brain, however in practice it is sufficiently reactive that this should not affect consumers^{citation needed}.

References

• http://plantphys.info/plants_human/fruitgrowripe.html
• http://www.actahort.org/books/398/398_17.htm
• http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=549760

Wikipedia content modification information:

• This page was last modified on 25 November 2008, at 11:33.

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