Chapter 18 The Chemistry of Food

1. Chapter 18The Chemistry of Food

2. You Are What You Eat • Our body parts are ultimately composed of atoms borrowed from food. • We use these atoms for about 75 years and then return them to the environment.

3. You Are What You Eat Between the mouth and the rectum, food is plundered of its nutritionally valuable biomolecules. Some molecules are oxidized to meet the body’s energy needs, while others are rearranged to make the necessary structures and components of the body.

4. Sugars, starches, and fibers in food Simple carbohydrates are easily and efficiently transported in the bloodstream. Remember glucose, fructose, and sucrose from Chapter 16 Lactose: Milk sugar Carbohydrates

5. Simple Carbohydrates • Glucose • Exclusive fuel of the brain • 4 Calories of energy per gram • Fructose • Sweetest of all sugars

6. Sucrose Digested to glucose and fructose, then into bloodstream Lactose Digested to glucose and galactose Lactose intolerance Lack of lactase, the enzyme that breaks down lactose Causes discomfort, flatulence, diarrhea Simple Carbohydrates

7. Concept Check 18.1 • Galactosemia is a rare genetic metabolic disease that affects the an individual’s ability to metabolize galactose. Failure to detect the disease early results in organ damage and has a 75% mortality rate in infants. Explain why infants are so profoundly affected by galactosemia’s effects and what can be done to manage the disease. • Hint 1: What is the primary component of an infant’s diet? • Hint 2: Where does the galactose come from?

8. Concept Check 18.1 Solution • The primary source of nutrition for infants is milk, which has a large amount of lactose. • Lactose is a disaccharide, that when digested, hydrolyzes to glucose and galactose. • Individuals with galactosemia lack the enzymes to further break down galactose, thus causing galactose to build up in cells causing damage. • Infants are routinely tested for galactosemia. If an infant is found to have galactosemia, it is kept on a strict lactose-free diet and can lead a relatively normal life.

9. Complex Carbohydrates • Most common complex carbohydrates (polysaccharides) are starch and fiber. • Starch has alpha linkages. • Digestible

10. Fiber has beta linkages Indigestible Fiber increases food bulk without adding significantly to caloric content. Good for the digestive tract, but can be overdone Carbohydrates should compose 45–64% of total caloric intake. Complex Carbohydrates

11. Proteins • The body produces only half of the amino acids it needs. • The remaining come from food (essential amino acids). • Meat, cheese, eggs, milk, grains, legumes, and nuts • During digestion, proteins are cut into amino acid components, which then enter the bloodstream. • Cells use amino acids to construct their own proteins. • Proteins can be metabolized at 4 Calories per gram, but the body does this only as a last resort.

12. Concept Check 18.2 • What substance in a vegetarian’s diet that would be considered a complete protein?

13. Concept Check 18.2 Solution • Most plant proteins lack one or more of the essential amino acids; therefore, there is no single substance that provides the vegetarian with a complete protein. • Vegetarians get around this limitation by combining several protein sources, such as combining a legumes (beans, peas, lentils, peanuts, and soy products) with a cereal grains (barley, cornmeal, oats, rice, pasta, and breads) or nuts and seeds (sesame seeds, sunflower seeds, cashews, and peanuts).

14. Workhorse Molecules • Physical structure, enzymes, hormones, oxygen transport, and antibodies • Proteins need ALL amino acids for proper functioning. • Must be obtained in the right proportions in the diet • Should compose 30% of total caloric intake • Complete proteins contain all of the essential amino acids in the right proportion. • Meat • Proper combinations of legumes and grains or nuts

15. Concept Check 18.3 • Which of the following are essential amino acids? • Valine • Glycine • Aspartic acid • Lysine

16. Concept Check 18.3 • The amino acids (a) valine and (d) lysine from the list are essential amino acids. • This means that they must come from food because the body cannot make them.

17. Fats and Oils • Dietary sources are primarily triglycerides. • From Chapter 16 • Saturated fatty acid side chains • Solids • From meats • Unsaturated side chains • Liquids • From plants • Sources: Meat, vegetable oils, butter, cheese, cream, egg yolks, ice cream

18. Fat Metabolism • Slower for fats than for carbohydrates • Lingering sense of fullness after ingestion • Reassembled to triglycerides before entering bloodstream • Nonpolar • Need lipoproteins to be carried in bloodstream • Transported for dismantling and reassembly into other fats • Used for energy directly (9 Calories per gram) • Stored in fat cells

19. Concept Check 18.4 • Give some common sources for unsaturated fats.

20. Concept Check 18.4 Solution • Oils from plant sources provide a good source of unsaturated fats. Examples include: • Corn oil • Safflower oil • Olive oil • Walnut Oil • Sesame seed oil

21. Cholesterol • Nonpolar compound found in animal foods • Integral part of hormone synthesis • Liver makes it • Excessive amounts lead to deposition on arterial walls. • Arteriosclerosis • Blockage leads to heart attack and/or stroke

22. Lipoproteins • Carry cholesterol in the bloodstream • Classified by their density • Low-density lipoproteins (LDL) • Transport cholesterol from the liver • Tend to deposit cholesterol on arterial walls • High-density lipoproteins (HDL) • Transport cholesterol to the liver • Tendency to reduce cholesterol deposition • Fats should compose less than 20% of total caloric intake.

23. Food provides energy for our bodies. It must either be used or stored. According to the first law of thermodynamics: Energy intake (food) = energy expended (used) + energy stored (fat) Caloric Intake and the First Law

24. Energy Intake

25. Concept Check 18.5 • Compare the different food types for caloric content per gram. Which food type has the greater caloric content, which one the least?

26. Concept Check 18.5 Solution • Fats have the highest caloric content at 9 Cal/g. • Carbohydrates and proteins each have 4 Cal/g. • Fiber is not digestible by humans, therefore, has no caloric content as a food that is eaten.

27. Energy Expended • Energy required to stay alive • Basal metabolism • Heart pumping, body temperature maintenance, and breathing • 0.5 Cal/hour per pound of body weight • Energy associated with exercise • Varies according to activity level

28. Calories Expended

29. Energy Stored • If energy intake exceeds energy used, the remainder is stored as fat. • Every 3500 Cal of excess intake means storage of 1 lb of fat. • Fat is energetically dense. • For every 3500 Cal energy output, the body burns 1 lb of fat (as long as fat is available).

30. Concept Check 18.6 • If a male who expends 2670 Cal/day wants to lose 6.0 lbs in 28 days, what should his daily caloric intake be?

31. Concept Check 18.6 Solution • First, calculate the number of Calories that need to be reduced per day: • Next, subtract the daily Calorie reduction needed by the total Calories usually expended: • Or, he can expend an additional 750 Cal/day than he normally does through exercise.

32. Essential in the diet, but have little to no caloric value Helpers in cell functions Nonpolar or fat soluble Vitamin A, vitamin D, vitamin E, vitamin K Stored in the body and not easily excreted Polar or water soluble Vitamin B, vitamin C Not stored by the body and easily excreted Vitamins

33. Fat-Soluble Vitamins: Vitamin A • Vision, immune defense, and maintenance of body lining and skin • Part of retinal pigments that absorb visible light • Liver, fish liver oils, milk, butter, eggs • Beta carotene in plant pigments • Carrots, squash, tomatoes, cantaloupe • Too much can have detrimental effects.

34. Fat-Soluble Vitamins: Vitamin D • Promotes absorption of calcium into the blood to be used for bone structure • Body can synthesize vitamin D with sun exposure. • Milk is vitamin D-fortified for children. • Too much vitamin D can cause deposition of Ca in soft body tissue. • Vitamin D deficiency causes rickets, which results in bone deformities. Example of rickets

35. Fat-Soluble Vitamins: Vitamin E • Antioxidant; prevents oxidative damage, especially to cell membranes • Widespread presence in food • Deficiencies are rare • Low toxicity

36. Fat-Soluble Vitamins: Vitamin K • Necessary for the synthesis of four proteins involved in blood clotting. • Present in leafy green vegetables and milk; synthesized by intestinal bacteria • Infants lack this bacteria, so they are given vitamin K at birth. • Overuse can result in blood clotting and subsequent brain damage. • Available only by prescription

37. Synthesis of connective tissue (collagen) Protection from infection Absorption of Fe Antioxidant Deficiency is called scurvy Common among early sailors “Limeys” Water-Soluble Vitamins: Vitamin C

38. Water-Soluble Vitamins: Vitamin C • Citrus fruits, leafy green vegetables, cantaloupe, peppers, tomatoes, mangoes • Water soluble • Excess is easily excreted. • Overuse can lead to nausea and cramping

39. B Complex Vitamins • Thiamine, riboflavin, niacin, vitamin B6, folate, and B12 • Central role in metabolism, protein synthesis, and cell multiplication • Spread through all food groups • B complex-containing grain hulls are removed during processing. • Milled grain frequently enriched • Deficiency results in irritability, depression, abnormal heart action, and skin problems

40. Concept Check 18.7 • Which of the following vitamins can be harmful if taken in more than the recommended amounts? • Vitamin A • Vitamin C • Vitamin D • Vitamin K

41. Concept Check 18.7 • Vitamins A, D, and K are fat-soluble and therefore can be stored in the body. Because of this, they can reach toxic levels if the intake exceeds amounts utilized by the body. • Consuming too much Vitamin A can result in blurred vision, hair loss and muscle soreness. • Excess amounts of Vitamin D can be deposited in the major organs. • Overuse of Vitamin K can lead to excessive blood clotting which can result in brain damage.

42. Minerals • Elements other than carbon, hydrogen, nitrogen, and oxygen that are needed for good health • Many are present in the body as ions rather than neutral atoms. • There are two groups of minerals, the major and minor groups, based on percent concentration in the body.

43. The Major Minerals • Compose about 4% of the body’s weight • Calcium • Structural material for bones and teeth, nerve signal transmission, and blood clotting • Persistent deficiency leads to osteoporosis • Phosphorus • Bound with Ca in bones and teeth, energy metabolism, and DNA • Sodium • Body fluid level regulation • Persistent excess leads to hypertension • Potassium and magnesium • Electrolyte balance in and around cells

44. The Minor Minerals • Present in trace amounts • Iodine • Involved in regulation of basal metabolic rate • Deficiency results in goiter • Iron • Composes a critical part of hemoglobin • Deficiency leads to anemia • Zinc • Enzyme functioning • Others • Selenium, chromium, and copper

45. Concept Check 18.8 • What is the role of iodine in the human body? • Where does it come from? • Is iodine classified as a major or minor mineral?

46. Concept Check 18.8 Solution • The thyroid is the only organ in the human body that uses iodine. The thyroid uses iodine to synthesize thyroxin, which is a hormone that regulates the basal metabolic rate. • Iodine is found in seafood and iodized salt (regular table salt with a small amount of sodium iodide added). • Individuals with an iodine deficiency can develop goiter, which is a swelling of the thyroid. • Iodine is classified as a minor mineral.

47. Food Additives • Long history (salt, sugar, vinegar) • Shift from rural to urban lifestyles requires preservation, packaging, and shipping • All additives regulated by FDA (25¢ of every consumer dollar spent) • GRAS: Generally Recognized as Safe • Salt, sugar, spices, sodium benzoate, and EDTA • New additions: Simplesse and Olestra • Five categories of additives exist.

48. Antimicrobial Agents • Added to prevent the growth of bacteria, yeasts, and molds • Botulism: A few nanograms will kill an adult • Salt (meat and fish) and sugar (jams and jellies) • Dehydrating conditions • Sodium benzoate, potassium sorbate • Canned, bottled, and packaged foods • Sodium nitrite • Makes meat pink • Inhibits growth of bacteria (including the one responsible for botulism) • Recent scrutiny

49. Antioxidants • Added to prevent oxidation • Unsaturated oils will oxidize in air • Products are volatile aldehydes, ketones, and acids • Foul odors and flavors—rancid • Common antioxidants are vitamin C, BHA, and BHT • Laboratory animals had lower cancer rates and longer lifespans than those without antioxidants in their diet. • BHA and BHT can be toxic. • Sulfites as a preservative • Wine and fruits • EDTA • Immobilizes metal ions that often catalyze oxidation

50. Fruits and fruit juice oxidize Foul smells can develop Brown color develops Fruit and Fruit Juice Oxidation