Principles of Food Science 5e, Textbook Page 138 (156 of 608)

138 Principles of Food Science O — — — — — CH2OH OH OH HO OH glucose H H H H H + O — — — — — CH2OH OH OH HO OH glucose H H H H H O — — —— — — — — CH2OH OH HO OH maltose H H H H H O — — — — CH2OH H2O OH OH O OH H H H H H + — —— O O — — — — — CH2OH OH OH HO OH glucose H H H H H + O — — — — HOCH2 CH2OH H HO HO OH fructose H H H2O + O — — — — — CH2OH OH HO OH H H H H H O — — — HOCH2 CH2OH H HO OH sucrose H H O — — — — — CH2OH OH OH HO OH glucose H H H H H + O — — — — — CH2OH OH OH HO OH galactose H H H H H O — — — — — — — CH2OH OH HO OH lactose H H H H H O — — — — — CH2OH H2O OH OH O OH H H H H H + Composition of Disaccharides 8-4 Two monosaccharide molecules combine to form one disaccharide molecule and one water molecule. Dairy producers offer a variety of lactose-free and lactose-reduced products. Examine the labels in the dairy case. Many stores stock milk that has 70% to 100% of the lactose removed. Some ice cream manufacturers also make lactose-reduced ice creams. Lactase is produced by Lactobacillus acidophilus bacteria, which normally live in the intestines. Antibiotics will kill these helpful bacteria while killing the bacteria that cause infections. Therefore, milk will sometimes be difficult to digest for several weeks after taking antibiotics. You can remedy this problem by eating a serving of yogurt shortly after finishing your antibiotic prescription. Be sure to choose yogurt that contains an active culture of Lactobacillus acidophilus. Nutrition News Lactose Intolerance Lactase is an enzyme that is present in the small intestines. Its presence is necessary for the digestion of milk sugar. Lactose intolerance is an inherited inability to produce the lactase enzyme necessary to properly digest lactose or milk sugar. Most Asian, Native American, and African American adults experience this problem to some degree. Symptoms of lactose intolerance include a sour after- taste when drinking milk. Gas, bloating, nausea, diarrhea, and flulike stomach cramps followed by constipation are other symptoms. People who are lactose intolerant can buy lactase from most pharmacies in either pill or liquid form. Experimentation with dosages will help them determine how much of the enzyme is needed to avoid symptoms when consuming milk products. The liquid lactase is usually added to milk and allowed to sit before drinking. The lactase will cause the milk to have a sweeter flavor. This is because the lactose is broken down into glucose and galactose. Copyright Goodheart-Willcox Co., Inc.

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138 Principles of Food Science O — — — — — CH2OH OH OH HO OH glucose H H H H H + O — — — — — CH2OH OH OH HO OH glucose H H H H H O — — —— — — — — CH2OH OH HO OH maltose H H H H H O — — — — CH2OH H2O OH OH O OH H H H H H + — —— O O — — — — — CH2OH OH OH HO OH glucose H H H H H + O — — — — HOCH2 CH2OH H HO HO OH fructose H H H2O + O — — — — — CH2OH OH HO OH H H H H H O — — — HOCH2 CH2OH H HO OH sucrose H H O — — — — — CH2OH OH OH HO OH glucose H H H H H + O — — — — — CH2OH OH OH HO OH galactose H H H H H O — — — — — — — CH2OH OH HO OH lactose H H H H H O — — — — — CH2OH H2O OH OH O OH H H H H H + Composition of Disaccharides 8-4 Two monosaccharide molecules combine to form one disaccharide molecule and one water molecule. Dairy producers offer a variety of lactose-free and lactose-reduced products. Examine the labels in the dairy case. Many stores stock milk that has 70% to 100% of the lactose removed. Some ice cream manufacturers also make lactose-reduced ice creams. Lactase is produced by Lactobacillus acidophilus bacteria, which normally live in the intestines. Antibiotics will kill these helpful bacteria while killing the bacteria that cause infections. Therefore, milk will sometimes be difficult to digest for several weeks after taking antibiotics. You can remedy this problem by eating a serving of yogurt shortly after finishing your antibiotic prescription. Be sure to choose yogurt that contains an active culture of Lactobacillus acidophilus. Nutrition News Lactose Intolerance Lactase is an enzyme that is present in the small intestines. Its presence is necessary for the digestion of milk sugar. Lactose intolerance is an inherited inability to produce the lactase enzyme necessary to properly digest lactose or milk sugar. Most Asian, Native American, and African American adults experience this problem to some degree. Symptoms of lactose intolerance include a sour after- taste when drinking milk. Gas, bloating, nausea, diarrhea, and flulike stomach cramps followed by constipation are other symptoms. People who are lactose intolerant can buy lactase from most pharmacies in either pill or liquid form. Experimentation with dosages will help them determine how much of the enzyme is needed to avoid symptoms when consuming milk products. The liquid lactase is usually added to milk and allowed to sit before drinking. The lactase will cause the milk to have a sweeter flavor. This is because the lactose is broken down into glucose and galactose. Copyright Goodheart-Willcox Co., Inc.

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Chapter 8 Sugar: The Simplest of Carbohydrates 139 There are several commonly used additives that are “sweet” alcohols. These alcohols are glycerol, mannitol, sorbitol, and xylitol. One source of glycerol is animal fats. See 8-5. Sources of Sugar Sugars have a sweet flavor and provide 4 kilocalories of energy per gram. Types of sugars commonly used as food ingredients are granulated, brown, and confec- tioners’ sugars honey corn syrup molasses and maple syrup. Food companies often use several kinds of sweeteners in a single food product. This allows food scientists to optimize sweetness for each product and minimize product costs. Each sweetener is listed separately in the ingredient list on product labels. Total carbohydrates are listed on the Nutrition Facts panel on a food label. Amounts Alcohols All organic compounds that contain at least one -OH group are called alcohols. Sugars are a related group of compounds that have multiple -OH groups plus an oxygen atom with a double bond. This similarity in chemical structure helps explain the high caloric content of most alcoholic (ethanol) beverages. Names of alcohols end in -ol. Examples include ethanol (ethyl alcohol), methanol (wood alcohol), and isopropanol (rubbing alcohol). All these alcohols are toxic if consumed in excess. Ethanol is the alcohol in alcoholic beverages. It can be made from any sugar or starch source. Small amounts of methanol in bad batches of “moonshine” have been known to cause permanent nerve damage, blindness, or death. Methanol is produced by burning wood without oxygen present. Isopropanol is derived from petroleum and is also not safe to consume. The Sweet Alcohols Glycerol Mannitol Sorbitol Xylitol Structure H C OH CH2OH CCH2OH HO C H CH2OH H C OH HO C H CH2OH H C OH H C OH CH2OH H C OH HO C H CH2OH H C OH H C OH CH2OH H C OH HO C H CH2OH Sources Exists in wine and beer By-product of soap manufacture Extracted from seaweed Fruits: apples, berries, pears, plums Seaweed and algae Apples, berries, plums, and other foods Description Warm, sweet, oily liquid Sweet, white, odorless crystalline solid Sweet, white powder, flakes, or granules Sweet, white, granules Kilocalories/ gram* 2.0 1.6 2.6 2.4 Uses Humectant1 in candy Solvent for colors and flavors Used in beverages, baked goods, gelatin, chewing gum, meat products, and commercial hot fudge sauces Texturizer2 in gum and candy Sweetener in sugar-free products but does contain calories and carbohydrates Texturizer, humectant, anticaking agent3, diabetic sugar substitute Texturizer, humectant, sugar subsitute Can be used in baking Cautions No limitations May worsen kidney disease Excess consumption may cause diarrhea Excess consumption may cause diarrhea 1 Humectants are additives that help products retain or hold on to moisture. 2 Texturizers are additives that give food products a desired mouth feel. 3 Anticaking agents are additives that keep powders or granules from lumping. * For comparison, mono- and disaccharides have 4 kcal/g. 8-5 The sweet alcohols are used as additives to serve a variety of functions in food products. Copyright Goodheart-Willcox Co., Inc.

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Chapter 8 Sugar: The Simplest of Carbohydrates 137 When scientists create diagrams of any ring-shaped organic compound, they simplify the drawing. They use the junction of lines to represent the location of a carbon atom. They draw lines where hydrogen atoms are located, but they do not write the letter H. In the following example, the diagram on the left shows glucose as a ring with all the atoms represented by letters. The diagram on the right is the shorthand version of the same molecule. C — O C — C OH OH OH H OHH — C C H — H H — C — H OH — H CH2OH C — O OH OH C C C — C OH OH All monosaccharides occur most frequently in a ring structure that contains five carbon atoms and one oxygen atom. They differ in the way the hydrogen and oxygen atoms are arranged around the ring. The difference in position affects the characteristics of the sugar and how it will respond in food preparation. To understand the importance of the arrange- ment of the atoms, look at two basic forms of glucose: α–D-glucose and β–D-glucose. As you can see from the following diagram, the alpha (α) glucose and beta (β) glucose have only one difference. That is the position of the -OH group on the right side of the ring. This one change in position determines whether the body is able to digest the sugar. Alpha-glucose is the basic energy source for humans. Beta-glucose is the main component of dietary fiber that provides bulk for the digestive track, but it provides no nutritive value because people cannot digest it. CH2OH OH OH C C CH2OH OH OH C C C — C OH OH C — C OH OH C — O C — O α - D - glucose β - D - glucose So far, the simple sugars described have a basic formula of C6H12O6. There are also some sugars that contain only five carbon atoms. These are riboses. The body uses them as the basic building blocks for ribonucleic acid (RNA). RNA carries the genetic code from DNA and is used for making protein. Disaccharides Sugars found in nature do not normally occur as monosaccharides. The sugar molecule’s structure enables it to readily combine with other sugars to form chains. A disaccharide is two joined monosaccharides. Most sugars consumed in the world are disaccharides. Sucrose, or table sugar, is a disaccharide that contains one glucose molecule and one fructose molecule. Other disaccharides found in the food supply are maltose and lactose. Maltose is commonly found in malted grains. It is made of two glucose molecules. This disaccharide is the least sweet. When in powder form, it is tan rather than clear or white like sucrose. Lactose is the sugar found in milk. It is composed of one glucose molecule and one galactose molecule. In pure form, it is white and contributes some of the color you associate with milk. When two monosaccharides join, a hydroxyl group from one and a hydrogen atom from the other separate to form water. See 8-4. This process of molecules joining and releasing water is reversible. Hydrolysis occurs when a large molecule, such as sugar, is divided into smaller parts by adding water. If you hydrolyze a molecule of sucrose, you will get one molecule of fructose and one molecule of glucose. The body uses this hydrolysis process to digest the disaccharides in food. For hydrolysis to occur, water must be present. This is why sweetened drinks are not as thirst quenching as plain water. Part of the water is used to digest the sugar and is not available for other functions. Three conditions can trigger hydrolysis. One condition is the presence of an enzyme to set off the reaction. A second condition is the addition of an acid. A third condition is the addition of heat. Digestion of sugar involves the addition of the enzyme sucrase. This enzyme is present in saliva. Thorough chewing of food enables the enzyme to be mixed into the food so the enzyme can work quickly. Lactose-free milk is produced by adding an enzyme to hydrolyze the sugar. Each type of sugar requires a different enzyme for hydrolysis to occur. You can determine the names of the enzymes by simply changing the -ose ending of the sugar to -ase. For instance, sucrase hydrolyzes sucrose and lactase hydrolyzes lactose. Sucrase is also known as invertase. This is because the fructose and glucose mixture that results from the hydrolysis of sucrose is sometimes called invert sugar. Copyright Goodheart-Willcox Co., Inc.

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Page 132Unit 3 Organic Chemistry: The Macronutrients click to expand contents

Page 238Unit 4 Food Chemistry: The Microcomponents click to expand contents

Page 324Unit 5 Food Microbiology: Living Organisms in Food click to expand contents

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