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Chemistry for Changing Times 11th Edition Hill and Kolb Chapter 16 Food John Singer Jackson Community College, Jackson, MI © 2007 Prentice Hall The Food We Eat Foods are chemicals. They include carbohydrates, fats, and proteins, along with water, vitamins, minerals, and fiber. Carbohydrates in the Diet The monosaccharides glucose (dextrose) and fructose, and the disaccharide sucrose are the most common dietary sugars. Carbohydrates in the Diet Digestion and Metabolism of Carbohydrates Glucose and fructose are absorbed directly into the bloodstream. Sucrose is hydrolyzed into glucose and fructose. Sucrose + H2O → Glucose + Fructose Carbohydrates in the Diet Lactose, found in milk, is hydrolyzed to glucose and galactose. Lactose + H2O → Glucose + Galactose Some people lack the enzyme necessary to hydrolyze lactose. This is known as lactose intolerance. Galactose is converted to glucose during metabolism. Some babies lack the enzyme (galactosemia) necessary for this conversion and require a synthetic formula for proper nutrition. Carbohydrates in the Diet Complex Carbohydrates: Starch and cellulose starch are polymers of glucose connected by alpha linkages; most animals and humans possess the enzymes necessary to hydrolyze starch to glucose that can then serve as a source of energy. Carbohydrates such as starch produce 4 kcal of energy per gram. Cellulose is a polymer of glucose connected by beta linkages; most animals and humans lack the enzymes necessary to hydrolyze cellulose, and it serves as a source of roughage or dietary fiber. Carbohydrates in the Diet Glycogen is the means by which animals store glucose. It is a highly branched polymer of alpha glucose. It is sometimes known as animal starch. Excess glycogen is stored as fat. Some bacteria found in the gut of termites and digestive tract of grazing animals can hydrolyze cellulose to glucose and these animals can use cellulose as a source of food. Fats and Cholesterol Fats are esters of fatty acids and glycerol. Some fat is metabolized for energy and produces 9 kcal of energy per gram. Some is used for cell membranes. Fats and Cholesterol Digestion and Metabolism of Fats Fats are digested in the small intestine. Enzymes called lipases hydrolyze triacylglycerols into mono and diacyl glycerols, fatty acids, and glycerol. Fats are stored in the body in adipose tissue in locations called fat deposits. Fat deposits are located around major organs beneath the skin. Fats and Cholesterol Fats and Cholesterol Dietary fats and cholesterol have been implicated in arteriosclerosis and cardiovascular disease. Deposits form on the inner walls of arteries called plaque. Normal Artery Hardened Artery Fats and Cholesterol Plaques that clog arteries are rich in cholesterol. Cholesterol is a fat-like steroid molecule that is common to animal tissue. Cholesterol is carried in the blood by lipoproteins. Lipoproteins are classified according to their density. Very low density lipoproteins (VLDLs) transport triglycerides. Low-density lipoproteins (LDLs) carry cholesterol from the liver to the blood and are responsible for the formation of plaques. LDLs are the so-called “bad” cholesterol. High-density lipoproteins (HDLs) carry the cholesterol to the liver and are the so-called “good” cholesterol. Fats and Cholesterol Fats and Cholesterol Diets high in saturated fats and trans fats have been linked to high LDL levels in blood. It is recommended that one limit the amount of saturated fat and trans fat in the diet. Trans fats are formed when unsaturated fats are hydrogenated in order to make margarines or more solid fats. Fats and Cholesterol Saturated vs. Cis vs. Trans Unsaturated Fats Proteins Proteins are digested into individual amino acids. These amino acids are used to synthesize proteins for growth and repair of tissue. The body can synthesize all but 9 amino acids necessary for protein synthesis. These 9 amino acids are called essential amino acids and include: Isoleucine, lysine, phenylalanine, tryptophan, leucine, methionine, threonine, and valine. Proteins Complete proteins contain all the essential amino acids needed for growth and repair of tissue. Lean meat, milk, fish, eggs, and cheese contain complete proteins. The human body requires about 0.8 g of protein per kg of body weight. Protein deficiency can lead to retarded growth and development, discoloration of the skin and hair, and swollen abdomen. Minerals: Inorganic Chemicals and Life Dietary minerals are the inorganic substances necessary for life. Bulk structural elements and macrominerals make up more than 99% of all atoms in the human body. Trace elements and ultratrace elements make up the rest. Minerals: Inorganic Chemicals and Life Minerals: Inorganic Chemicals and Life Lack of dietary minerals can have serious consequences. Lack of iodine in the diet can lead to thyroid goiters. Vitamins Vitamins are organic compounds that are essential in the diet. Vitamins do not include proteins, fats, carbohydrates, and minerals. Vitamins can be classified as either fat-soluble or water-soluble. Vitamins Fat-Soluble Vitamins Vitamins Water-Soluble Vitamins Vitamins Vitamins Vitamin deficiency can be serious. (a) Softened bones due to deficiency of vitamin D. (b) Pellagra due to deficiency of niacin. Other Essentials: Fiber and Water Dietary Fiber Fiber may be soluble or insoluble. Insoluble fiber is mostly cellulose while soluble fiber is mostly gums and pectins. Fiber has a number of benefits. It helps to maintain proper colon function, and may help to control blood sugar and lower cholesterol levels. Other Essentials: Fiber and Water Water Water is an essential part of our diet. Actually, most of what we ingest is water. In addition we require 1-1.5 L of water daily. Starvation and Fasting Starvation is the total deprivation of food. It takes less than one day for the body to deplete itself of glycogen stores. After the glycogen is depleted, the body will then metabolize the fat reserves. Fat metabolism leads to ketosis as ketone bodies are released into the blood and urine. This can lead to acidosis as the blood pH drops. Body proteins will also be metabolized and eventually muscle proteins will be metabolized. Starvation and Fasting Ketone Bodies Starvation and Fasting Malnutrition can also occur due to eating too much processed food. Processing of food removes much of the nutritional value and fiber. It is ironic that people in developed nations experience obesity and poor nutrition while living in a land of food abundance. Food Additives Food additives are substances other than basic food stuffs added to food as a result of production, processing, packaging, or storage. Sugar, salt, corn syrup, citric acid, baking soda, vegetable colors, mustard, and pepper make up more than 98% of all additives by weight. Food Additives Additives That Improve Nutrition KI: added to salt to prevent goiter Vitamin B1: added to polished rice Vitamin C: added to fruit juice and other beverages Vitamin D: added to milk to prevent rickets Vitamin A: added to margarine to match nutritional value of butter Food Additives Flavoring Agents Food Additives Artificial Sweeteners Food Additives Artificial Sweeteners Food Additives Flavor Enhancers A popular flavor enhancer is monosodium glutamate (MSG). Excess MSG can be harmful. It has been shown to cause birth defects if eaten in large amounts by pregnant women. Food Additives Spoilage Inhibitors Antimicrobials prevent spoilage from molds, yeasts, or bacteria. Propionic acid, sorbic acid, benzoic acid, and their salts can be used. Food Additives Spoilage Inhibitors Sodium nitrate (NaNO2) is used to cure meats and gives the pink color to ham, hot dogs, bacon, and bologna. However, stomach acid converts the nitrite ion to nitrous acid which can then react with amines to form nitrosoamines, which are known carcinogens. Food Additives Antioxidants: BHA and BHT Foods that contain fats can turn rancid due to the formation of free radicals. Antioxidants react with free radicals, preventing their chain reaction formation. Antioxidants include butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), tertbutylhydroquinone, and propyl gallate. Food Additives Antioxidants Food Additives Food Colors Food Additives Food Colors Some food colors such as FD & C Orange No. 1 have been banned by the FDA. Others have been found to be carcinogens. Even so, they present little risk since they are used in such small amounts. Poisons in Our Food Carcinogens Foods contain both natural and added carcinogens. Scientists estimate that we consume natural carcinogens at 10,000X the rate of synthetic carcinogens. Poisons in Our Food Incidental Additives Incidental additives get into food accidentally during production, processing, packaging, or storage. About 10,000 incidental additives end up in our food. Some have been causes of concern, including Alar (its breakdown product is dimethylhydrazine, a suspected carcinogen), PCBs, PBBs, antibiotics, DES, etc. A World Without Food Additives Food additives are likely a necessary part of a modern society. Each year in the U.S., there are 76 million illnesses, including 5000 deaths due to bacteria, viruses, and parasites in food. Few if any deaths are associated with the use of intentional food additives. Green Plants: Sun-Powered Food Making Machines Green plants contain chloroplasts. These organelles have the ability to convert solar energy into food energy. 6 CO2 + 6 H2O + solar energy → C6H12O6 + 6 O2 Green Plants: Sun-Powered Food Making Machines In an early agricultural society, people grew plants for food and obtained energy from food. Green Plants: Sun-Powered Food Making Machines Shown here is the flow of nutrients in a simplified system. Farming with Chemicals: Fertilizers Fertilizers are used to replace plant nutrients that agricultural activities remove from the soil. There are three primary plant nutrients: nitrogen, potassium, and phosphorus. Farming with Chemicals: Fertilizers Nitrogen Nitrogen from the atmosphere is unavailable for plant use. Legumes contain bacteria in root nodules capable of fixing nitrogen; lightning can also fix nitrogen. Anhydrous ammonia or nitrogen-containing fertilizers are also used to replace nitrogen removed from soil by crops. Farming with Chemicals: Fertilizers Phosphorus Phosphorus is used by plants in the phosphates of DNA and RNA as well as ATP. Animal bones and the ore rock phosphate are sources of phosphates that can be converted to fertilizer. Farming with Chemicals: Fertilizers Potassium Potassium ions (K+) are taken up by the plants and used to balance fluids in cells. They are also involved in formation and transportation of carbohydrates and may be involved in protein synthesis. The most common form of potassium in commercial fertilizers in KCl. Farming with Chemicals: Fertilizers Other Essential Elements In addition to the three major nutrients, three secondary plant nutrients, magnesium, calcium, and sulfur, are needed in moderate amounts. Also, eight micronutrients are needed in smaller amounts. Farming with Chemicals: Fertilizers Farming with Chemicals: Fertilizers The “complete fertilizers” that are purchased by farmers and home gardeners usually only contain the three major plant nutrients. The numbers on the fertilizer bags/boxes, such as 5-10-5, give the percentage of N, P2O5, and K2O, respectively. The War Against Pests Insects have always been a problem involved with our food production. Insecticides are used to kill insects. The War Against Pests DDT was developed shortly before World War II and was at one time considered to be an ideal insecticide. Its widespread use has saved many human lives from disease and at the same time has caused much environmental damage. The War Against Pests DDT is a persistent chemical substance; that is, it does not break down in the environment. It is fat soluble and concentrates in fatty tissues. It is biologically magnified and causes the disruption of calcium metabolism. Its use has been documented to cause the decline of fish-eating birds. The War Against Pests Organic phosphorus insecticides have been developed that are less persistent than DDT. Most are more toxic to mammals than DDT. Malathion is less toxic than DDT. The War Against Pests Carbomates are another family of insecticides. Most are narrow-spectrum insecticides that are only directed at one or a few insect pests. They break down easily in the environment and do not accumulate in fatty tissue. Biological Insect Controls Parasitic, predatory organisms, microbes, or viruses can be used to destroy target insects. The release of sterile insects to ineffectively mate with wild insects can reduce a population. Pheromones can be used to attract and trap certain insects. Juvenile hormones have been approved by the EPA to control mosquitoes and fleas. They prevent the non-reproducing larvae stage from forming adults. Herbicides and Defoliants Herbicides are used to kill weeds and defoliants cause leaves to fall off plants. Herbicides and Defoliants 2,4-D and 2,4,5-T 2,4-D (2,4-dichlorophenoxyacetic acid) was introduced in 1945. It is an herbicide that is effective against newly emergent, broad-leafed plants. 2,4-D can be purchased in garden supply stores. 2,4,5-T (2,4,5-trichlorophenoxyacid) is a defoliant that is effective against woody plants. 2,4-D and 2,4,5-T were mixed as a product called Agent Orange that was used in Vietnam to defoliate the jungle and kill crops of the enemy. Unfortunately, 2,4,5-T contained a contaminant called dioxin that led to birth defects and potential cancers. The EPA banned 2,4,5-T in 1985. Herbicides and Defoliants Atrazine and glyphosphate are the most widely used herbicides in the U.S. Atrazine binds to protein in chloroplasts and shuts down photosynthesis. Atrazine is used on corn crops. Corn is resistant to Atrazine. Glyphosphate is a nonselective herbicide that is metabolized by soil bacteria. Therefore, other plants can be grown on the soil shortly after use. It is sold by the trade name Round-Up®. Herbicides and Defoliants Paraquat is a preemergent herbicide that inhibits photosynthesis by accepting electrons that would be used to reduce carbon dioxide. It kills weeds before crop seedlings can emerge and it is rapidly broken down in the soil. Sustainable Agriculture Conventional farming uses pesticides and fertilizers that have negative environmental consequences. Conventional farming is also energy-intensive. Organic farming does not use synthetic fertilizers or pesticides. It provides lower yields than conventional farming but is more labor-intensive. Some Malthusian Mathematics Thomas Robert Malthus stated in 1830 that the human population increases faster than the food supply. Unless population growth is controlled, poverty and war will be limiting factors. Populations grows geometrically and the food supply grows arithmetically. Some Malthusian Mathematics The irony is that in the developed world, food is abundant and obesity is a concern, while in the developing world, malnourishment is still a fact of life. Can We Feed a Hungry World? The Earth’s population continues to grow. Modern agriculture has greatly increased our food production. At some point, limiting factors will affect the human population. The only questions are when and how? We can reduce the birth rate and/or increase the death rate through war, famine, pestilence, or destruction of our environment.