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

8. Fiber has beta linkages Indigestable 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

9. Proteins • The body produces only half of the amino acids it needs. • The remaining come from food. • 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.

10. 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 • Meat • Proper combinations of legumes and grains or nuts

11. 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

12. 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

13. 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

14. 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.

15. 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

16. Energy Intake

17. 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

18. Calories Expended

19. 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).

20. 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 Polar or water soluble Vitamin B, vitamin C Vitamins

21. 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.

22. 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.

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

24. 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

25. 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

26. 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

27. 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

28. 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.

29. 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

30. 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

31. 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.

32. 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

33. 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 • Wine and fruits • EDTA • Immobilizes metal ions that often catalyze oxidation

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

35. Artificial Colors • Added to improve appearance • Natural plant pigments • Synthetic dyes • Use is purely aesthetic • Red dye no. 3 • Delaney Clause • Forbids the addition of any substance shown to cause cancer in animals, regardless of dose.

36. Artificial Flavors and Flavor Enhancers • Artificial flavors • Can be natural or synthetic versions of the same molecule • Sweeteners • Sugar, corn syrup, aspartame • Plant flavors • Wintergreen, peppermint, ginger, vanilla, almond extract • Flavor enhancers • No flavor of their own, enhance flavors in general • MSG (monosodium glutamate)

37. Added to improve and preserve the physical characteristics of food Humectants Added to keep food moist Anti-caking agents Added to powders to keep them dry and granulized Emulsifiers Added to keep polar and nonpolar ingredients mixed Stabilizers

38. Sunlight Water Carbon dioxide PHOTOSYNTHESIS: Light + 6CO2 + 6H2O  C6H12O6 + 6O2 Plants need other elements from the soil to synthesize lipids, nucleic acids, and proteins. Molecules Used to Grow Crops

39. Fields that get repeated use to grow crops become depleted of some of the necessary elements. They must be replaced by fertilizers. Primary Nutrients

40. Potassium • Used by plants in its ionic form, K+ • Chemical potassium fertilizers • Potassium chloride: KCl • Potassium sulfate: K2SO4 • Mineral deposits of potassium are located in Germany, Russia, and Canada.

41. Nitrogen • Used by plants for the synthesis of amino acids • Normally absorbed as ammonium ions (NH4+) or nitrate ions (NO3-) • Can’t be used in its elemental form • Fixed nitrogen • Crop rotation • Soybeans and peas grow nitrogen-fixing bacteria in their roots. • Nitrogen fertilizers • Haber process (3H2 + N2 2NH3) • Urea, ammonium nitrate, ammonium sulfate

42. Phosphorus • Absorbed in ionic forms, as phosphates • H2PO4- • HPO4- • Made by treating phosphate rock (calcium phosphate with sulfuric acid) to form superphosphate

43. Most fertilizers are numbered to indicate the percentage of nitrogen, phosphorus (as P2O5), and potassium (as K2O). For example: 5, 15, 5 Fertilizer

44. Secondary Nutrients • Secondary nutrients • Calcium, magnesium, and sulfur • Micronutrients • Boron, chlorine, copper, iron, manganese, molybdenum, sodium, vanadium, and zinc

45. Molecules Used to Protect Crops • Used to control pests and weeds that carry disease, damage crops, or provide a nuisance • One third of the world’s total crops are destroyed by pests or weeds. • Insecticides • Early ones were highly toxic (Hydrogen cyanide) • DDT and HCB came next • Stunning successes • Relatively nontoxic to humans

46. Molecules Used to Protect Crops Bioamplification Levels of DDT contamination concentrated as DDT moved up the food chain American bald eagle almost driven to extinction The chemical stability of chlorinated hydrocarbons allowed them to accumulate in soil and water supplies.

47. Modern Insecticides • Organophosphates • Malathion and parathion • Broad-spectrum • More toxic to humans and pests than chlorinated hydrocarbons • BUT they degrade quickly in the environment • Carbamates • Carbaryl and aldicarb • Narrow-spectrum • Toxic but degradable

48. Herbicides • Used to kill weeds and unwanted plants that compete with and dominate crop species • 2,4,5-T and 2,4-D are defoliants

49. Agent Orange • Agent Orange is a 1:1 mixture of 2,4-D and 2,4,5-T • Defoliants are banned due to the unavoidable presence of dioxin as a contaminate. • Dioxins are both toxic and carcinogenic.

50. Triazine Herbicides • Atrazine • Destroys weed in cornfields • Low toxicity to mammals • Metolachlor • Soybean and corn crops • No accumulation/bioamplification • Paraquat • Marijuana • No accumulation/bioamplification