Sugar

Sugar

Sugar, from the Greek word saccharis, is a term with a variety of meanings. To the biochemist, sugar is a broad term covering a large group of related organic compounds , all of which are composed of carbon, hydrogen, and oxygen. Green plants utilize their chlorophyll to transform solar energy (sunlight) into chemical energy by converting carbon dioxide and water into plant sugars through the process of photosynthesis. Generally, when people speak of sugar, they are referring to sucrose, which is a disaccharide or double sugar composed of equal parts of glucose and fructose. Glucose and fructose are monosaccarides or single sugars, found in fruits and in honey (together with sucrose). There are hundreds of different sugars and these are only a small section of the vast family of carbohydrates, which includes cellulose at one end of the scale and simple alcohols at the other. Starches, also made by plants, are dense complexes of sugar molecules. Starches and sugars make up the group of foodstuffs known as carbohydrates. All carbohydrates are formed originally by photosynthesis.

Sources of Natural Sugar

Sucrose, fructose, dextrose, and glucose are the natural sugars most frequently used. Although many fruit-bearing plants like the date palm and the carob produce sugar as a product of photosynthesis, the world's major supply of sugar is obtained from the cultivated or managed crops of sugarcane, sugar beet, corn, sugar maple, and sweet sorghum. Sugarcane, corn, and sweet sorghum are cultivated grass plants that store sugar in their stalks or seed. Sugar beet is a broadleaf plant that stores sugar in its root. Sugar maple is a hardwood tree with sugar in its sap, and honey is produced by honey bees from the nectar of plant flowers that contains sugars.

Sugar, Calories, and Energy

In addition to its flavor, which was the original reason for its popularity, sugar supplies an important nutritional factor in the form of energy. Sugar contains four calories per gram and one teaspoon of white table sugar (sucrose) weighs about 3.5 grams. The basic calorie requirement for maintaining life (respiration, circulation, muscle tone) varies between 750 and 1,630 per day in a state of complete rest. Intense muscular effort may require upwards of 7,000 calories during the day. Carbohydrates are an essential component of the human diet, and Recommended Dietary Allowances (RDAs) for nutrients in the American diet have been established by the National Academy of Sciences. The RDAs suggest that the average dietary energy intake (in calories) should consist of 10 to 15 percent protein, 35 to 40 percent fat, and 45 to 50 percent carbohydrates. Carbohydrates, therefore, contribute the major part of the available energy in the human diet. In less-developed areas, it is not unusual to find 80 to 90 percent of available energy in the diet coming from carbohydrate sources.

To get the energy needed, humans reverse the process that plants utilize to make sugar. Digestion of sugars (carbohydrates) is accomplished by enzymes beginning in the mouth and continuing in the small intestine. In the cells of the human body, all usable carbohydrates are converted to the same basic fuel, pyruvic acid , which is then burned to release energy, stored as fat for future energy needs or converted to intermediates for growth or maintenance of body tissue. Although proteins and fats can also be used as sources of energy, only sugars can yield pyruvic acid. That is why sugar is the principal and preferred fuel for the body's energy cycle.

Social and Environmental Impact

During its long history, sugar has been the cause and prize of wars, as well as the object of political activity. There are logical reasons for this. Sugar is an attractive commodity and thousands of people throughout the world gain their livelihood from sugar. With a rapidly expanding world population, this is important because sugarcane and sugar beet are, respectively, the most efficient plant fixers of solar energy among tropical and temperate-zone vegetation. Sugarcane is four times as effective as any tropical plant in terms of dry-matter production per unit of land, and sugar beet is twice as productive as any temperate-zone plant. It requires an average of only 0.07 hectare (0.17 acre) to fix solar energy to the equivalent of one million kilocalories of energy in the form of sugar. All other forms of edible energy require more. Beef is at the top end of the scale, needing 7.7 hectares (19 acres)—more than one hundred times as much land as needed for sugar.

Processing and Marketing

Crystallized sugar, which is the basic commodity of the international sugar trade, comes from sugarcane, grown in warm, moist climates, and sugar beet, grown in temperate climates. Juice containing sugar is extracted from the stalks of sugarcane and from the roots of sugar beet. The process of crystallization separates sugar out of a sugar-saturated solution. It begins by the formation of minute crystals that act as nuclei for the growth of larger ones. The size of the crystals is controlled by temperature. The uniform small crystals in table or white sugar are the result of controlled crystallization.

Sugar in the international market is under the review of members of the International Sugar Agreement. About 70 percent of the world's sugar supply is consumed in the areas in which it is grown. Twenty percent is marketed through agreements or some form of preference. The remaining 10 percent is world market or free market, and is sold at a price that has no relationship to the cost of production.

Total caloric sweetener consumption in the United States is about 130 pounds per capita each year. Use of refined sugars (from sugarcane and sugar beet) has declined from 67 percent of total caloric sweeteners (84 pounds) in 1980 to less than 49 percent (63 pounds) in 1999. The principal reason for this decline is the increased per capita consumption of corn sweeteners, especially high fructose corn syrup. The approval of the artificial sweetener aspartame (for example, Nutrasweet) for table and industrial use in 1982 is another reason for this decline.

see also Carbohydrates; Economic Importance of Plants; Grasses.

Garry A. Smith

Bibliography

Clark, Margaret A., and Mary Ann Godshall, eds. Chemistry and Processing of Sugar-beet and Sugarcane. New York: Elsevier, 1988.

Patura, J. M. By-products of the Cane Sugar Industry, 2nd ed. Amsterdam: Elsevier, 1982.

Smith, Garry A. "Sugar Myths and Majesties." Sugar Journal 61 (1998), nos. 2, 3, 4.

——. "Sugar Beet." Principles of Cultivar Development, Vol. 2, ed. Walter R. Fehr. New York: Macmillan, 1987.

——. "Sugar Crops." CRC Handbook of Plant Science in Agriculture, Vol. 2, ed. B. R. Christie. Boca Raton, FL: CRC Press, 1987.