Most of the citrus fruits originated as subtropical plants from Southeast Asia, about 4,000 years ago. Their watery pulp apparently evolved as an adaptation to the dry component of the monsoon cycle. The citrus fruits include the citron, several variants of the orange, lemon, lime, mandarin, kumquat and, as a later development, the grapefruit.
World production of citrus plants today averages about 50 million metric tons annually. Oranges make up about two-thirds of that total production. About one-fourth of all citrus fruit produced worldwide is consumed in the United States. The citrus fruit that we eat is the ovary of the plant, with each segment, called a "carpel," being a compartment of the ovarian structure. Juice cells of the pulp fill up with a sap, providing the "flavor" and high carbohydrate constituents.
Generally, as native products, most citrus fruits are fairly low in total calories. They contain little or no starch. Thus, they will not generally sweeten very much after picking. The fruit therefore, must reach its desired balance of sugar and acid on the tree, before it is harvested. The color of the citrus fruit usually coincides with a drop in temperature. In warm climates where the temperature does not drop, such as in parts of the tropics, oranges will usually remain green. Citrus fruits commercially processed may be treated with ethylene, or by other means, to "improve" their color to our "trained" expectations.
It is generally a perception that the citrus fruits are rich in vitamin C, and historically limes and other citrus products were given to sailors to prevent vitamin C deficiency, or scurvy. Actually, most of the vitamin C is in the peel or in what is called the albedo (the white layer just under the peel) rather than in the pulp.
The citron, which is an egg-shaped fruit, is the largest (up to ten inches long) of the citrus family. The citron tree is small and thorny. It was grown in ancient times and may have been the earliest of the citrus fruits cultivated and used by man. The citron was brought from the Orient to the Middle East, where it was known in antiquity as the "Persian apple." It is widely held that the Persian leader, Cyrus the Great, transported the citron westward when he conquered Babylon in 539 B.C. The citron was then distributed throughout the Mediterranean crescent by the Greeks, under Alexander the Great in 300 B.C.
In biblical times, the citron was cultivated in Palestine by the Jews, who used a smaller variant, the etrog, in part as an offering at the Feast of the Tabernacles. The citron became one of the symbols of resistance to Roman rule in the first century A.D., and the image of the fruit replaced the Emperor Nero on Jewish coins of the time. With the diaspora, the citron was carried throughout the Mediterranean and to southern Europe. The Romans grew citron trees widely in Italy throughout the reign of Caesar Augustus and thereafter. Some of the very first greenhouses, constructed out of a mica-like "glass," were developed to protect the citron tree through the winters in Northern Italy.
On the tree, the citron fruit looks somewhat like a "rough-skinned" lemon. Americans know the citron through the consumption primarily of its candied peel, which is derived from the very thick rind of the fruit. Compared to other crops, however, worldwide production of citron fruit is very small. The plant grows only in tropical and subtropical climates. Thus, most of the citron production still originates in the Mediterranean area, primarily in Israel, Greece, Italy, Corsica, Sicily and southern France. Some citron is grown in Florida and in California in this country. It cannot be grown in cold weather climates.
When harvested, the citron fruit is cut open and soaked in a solution, usually containing salt, calcium chloride to keep the peel firm, and sulfur dioxide, which serves as a preservative. Once cured, the salt is removed by soaking the rind in hot water. The remaining peel is then candied by soaking it in sugar solutions. Most of the sugar-embedded citron peel is carbohydrate, supplying about 314 calories per 100 grams. Without sugar impregnation, however, the native peel contains only about 20 to 50 calories per 100 grams.
The peel has a unique taste, differing from that of other citrus plants. The candied peel can be consumed alone, but more commonly it is added to cakes, cookies, candies, desserts and other preparations. The citron pulp, which is relatively small in amount, is too acidic to eat. Any of the citrus fruit peels are a good source of fiber and potassium. The processed citron peel contains a lot of sodium (close to 300 milligrams per 100 grams). The candied, citron peel contains an aldehyde, citral, that neutralizes vitamin A obtained from other dietary sources.
Historically, other citrus plants were initially treated more as ornamental and spice plants, until perhaps the 15th century A.D. or so. All were from the Far East in origin, except for the grapefruit, which was developed in the 18th century in the West Indies, as a cross between the orange and the pummelo, another new but all forgotten citrus plant.
In the coming weeks, several columns will be devoted to individual citrus fruits that we consume in great abundance in this country.
Dr. Huber is the director of the Texas Nutrition Institute, a not-for-profit program serving the needs of the people in East Texas. Do you have a question or a topic idea for Dr. Huber? E-mail him at
huber1997@aol.com.
Source:
http://www.tylerpaper.com/article/20080227/FOOD/802270301 
