135 S cientists estimate that more than 50% of the earth’s biomass is made of carbohydrate compounds. (Biomass refers to the dry weight of all plants and animals.) About 75% of the dry mass of all land plants and seaweed are carbohydrates of some form. This includes the plants used to make such products as wood, paper, cotton, linen, and rayon. Because of their abundance throughout nature, carbohydrates make up the bulk of the biomass in food. Carbohydrates are a major source of energy for humans, providing 55% to 80% of calorie needs. Compared with people in other countries, people in the United States have one of the lowest carbohydrate intakes. Even so, these organic compounds still provide the bulk of energy in the US diet. See 8-1. Carbohydrates provide a reserve energy store for all living things and form the vital structure of living cells. Even DNA, which provides genetic information to all living things, is composed of a carbohydrate base. Understanding the functions of carbohydrates is important to many areas of industry and research however, it is vital to food science. You will rarely work with a food mixture that does not contain carbohydrates in some form. You can group carbohydrates in food ingredients into three categories: sugars, starches, and fiber. In this chapter, you will examine the structures and functions of sugars. Carbohydrate Production All carbohydrates are compounds composed of the elements carbon, oxygen, and hydrogen. The name carbohydrate means a hydrate of carbon, or carbon that is bound with water. This is because scientists originally felt the molecular structure was carbons bonded to an equal number of water molecules—Cx(H2O)y. Although they quickly abandoned this view, the name carbohydrate has remained. Carbohydrates are nature’s means of storing solar energy. Through the process of photosynthesis, plants convert energy from the sun into the most common of the carbohydrates, glucose. Photosynthesis requires carbon dioxide, water, chlorophyll, and sunlight. Sunlight is the source of energy that powers the chemical reaction of photosynthesis. Chlorophyll is a green pigment found only in plants. It traps the radiant energy from the sun and turns it into chemical energy. All green plants use this process for growth as well as energy storage. The equation for photosynthesis is 6CO2 + 6H2O + sunlight C6H12O6 + 6O2 carbon dioxide + water + energy glucose + oxygen (simple sugar) Initially, all carbohydrates in plants are produced in the form of glucose. Plants can then convert glucose into whatever form of sugar, starch, or fiber they need at the time. As the plant matures, it turns glucose into fiber to form the structure of the stems and leaves. As the plant reaches full size, it begins to transfer its energy into sugars and starches. These are storage forms of Key Terms carbohydrate photosynthesis saccharide hydroxyl group monosaccharide fructose glucose galactose ribose ribonucleic acid (RNA) disaccharide sucrose maltose lactose hydrolysis invert sugar alcohol molasses dextrose solubility supersaturated interfering agent agitation ripening caramelization glycogen added sugar empty calories diabetes mellitus insulin Yulia_Davidovich/iStock/Getty Images Plus 8-1 Most calories in a meal should come from carbohydrates in fruits, vegetables, and whole grains. Copyright Goodheart-Willcox Co., Inc.