chapter 16 food: those incredible edible chemicals
TRANSCRIPT
Chapter 16 Food: Those Incredible Edible
Chemicals
Chapter 16 2
Food • Three main classes:
– Carbohydrates– Fats– Proteins
• Also need:– Water– Fiber– Vitamins– Minerals
Chapter 16 3
Carbohydrates
• Sugars– Used as sweetener– Absorbed directly into bloodstream
• Come in several forms: glucose, fructose, sucrose
• Lactose, milk sugar, digested by nearly all human babies, but few adults lack enzyme to start breakdown
Chapter 16 4
Complex Carbohydrates
• Starch: digestible polymer of glucose– Releases glucose when broken down– Supply 4 kcal/gram– Store small amounts in liver and muscle: glycogen
• Cellulose: indigestible polymer of glucose– Also known as fiber– Most abundant carbohydrate– No caloric value
Chapter 16 5
Fats
• High-energy food– 9 kcal/gram
• Build and maintain cell membranes
• Mainly triglycerides– Ester of glycerol and fatty acids
• Stored in adipose tissue– Insulate vital organs from shock– Insulate body against temperature changes
Chapter 16 6
Chapter 16 7
Saturated Fats
• Implicated in arteriosclerosis– Hardening of arteries
• Strong correlation between them– Typically need cholesterol as well
• Deposits form on inner walls of arteries• Blood clots get lodged
– Stroke, if it occurs in brain– Heart attack, if in heart
Chapter 16 8
Lipoprotein
• Group of proteins combined with a lipid– typically triglycerides and cholesterol
• Classified according to density
Chapter 16 9
Fats and Cholesterol in Blood
• Not all fats are bad– Prefer mono-unsaturated fats found in olive and
canola oil– Polyunsaturated fats may also be good
• Natural unsaturated fats are cis isomers
• Adding hydrogen may produce trans isomers– May raise cholesterol levels
Chapter 16 10
Chapter 16 11
Proteins
• Broken down into amino acids– Used mainly to produce useful proteins– Produce: muscle, hair, enzymes, …– Only excesses used for energy production
• Body can synthesize all but eight amino acids– Essential amino acids– Combined plant sources to get all of them
Chapter 16 12
Minerals
• Also known as dietary minerals– about 4% weight of human body
• Some used for bulk and structural uses
• Ultra-trace elements: need only at very low levels– Some have no known function
• Too much of any mineral may be toxic
Chapter 16 13
Chapter 16 14
Vitamins
• Specific organic compounds required in the diet to prevent specific diseases
• Two broad classes
• Fat soluble– Store excess– May lead to overdose
• Water soluble– Excrete excess– May be lost during cooking
Chapter 16 15
Dietary Fiber
• Takes up space in stomach
• Insoluble fiber: made of cellulose– May prevent some digestive problems
• Soluble fiber: made of sticky materials– Help remove bile acids that digest fat– May slow sugar absorption
Chapter 16 16
Water
• Makes up most of the food we eat
• Require 1–1.5 L of water per day– May need more after exercise or on hot
days
• Carbonated beverages long ago replaced water as beverage consumed most in U.S.
Chapter 16 17
Starvation
• Human body deprived of food• Weakening during starvation, makes
you more susceptible to disease• Body consumes itself in order to get
energy– Glycogen– Fat tissue– Muscle
Chapter 16 18
Processed Food
• Processing removes some of the nutrients
• Nutrients may also be removed by cooking process
• Manufacturers may add important vitamins and minerals back to food – Not all nutrients are necessarily added
back
Chapter 16 19
Food Additives
• Substances other than basic foodstuffs that are present in food as a result of some aspect of production, processing, packaging, or storage
• Sugar, salt, and corn syrup used in greatest amounts
• Used since ancient historic times
• In U.S., regulated by FDA
Chapter 16 20
Additives
• Enrichment: adding nutrients back to foods
• Many spices and flavoring agents added to improve taste – Some flavoring agents have been purified
and used directly– When used in moderation, present little in
health hazards
Chapter 16 21
Artificial Sweeteners• Developed to help combat obesity
• Tend to be polyhydroxy compounds
• Varying amounts of sweetening ability
Chapter 16 22
Flavor Enhancers
• Do not have much flavor
• Enhance other flavors
• Most common one is table salt– Enhances sweetness and may mask
bitterness and sourness
• Also use monosodium glutamate (MSG)
Chapter 16 23
Spoilage Inhibitors
• Inhibit growth of bacteria and molds– Common ones include NaNO2 and SO2
• Prevent oxidation of foods– Occurs when fats go rancid– Usually occurs by production of free
radicals– Use antioxidants to prevent this from
happening
Chapter 16 24
Food Coloring
• Expectation that foods will have certain colors– Would you drink bright blue milk?
• Many dyes exist to color food
• Label must clearly indicate if artificial colors are present
Chapter 16 25
Poisons in Food
• Some are natural– Botulism toxin– Oxalic acid– Aflatoxins
• Some cause cancer– Aflatoxins
• Some are toxic– Botulism toxin
Chapter 16 26
Incidental Additives
• Get in accidentally during production, packaging, or storage
• May include: pesticide residues, insect parts, and antibiotics given to animals– Antibiotics used to promote weight gain– Government-accepted levels of insect
parts in grain – impossible to remove all
Chapter 16 27
Life Without Additives?
• Food would be blander– No spices or flavor enhancers
• More rapid spoilage of food– Would reduce amount of food available
• Possible vitamin or mineral deficiencies
Chapter 16 28
Growing Food
Chapter 16 29
Fertilizers
• Three primary plant nutrients:– Nitrogen, potassium, and phosphorus
• Add them to increase crop production
• Replace lost nutrients in soil
• Allows support of more people on a given area of farmland
Chapter 16 30
Nitrogen• Some plants fix nitrogen out of air
– Legumes: e.g., clover and peas
• Rotate with nitrogen-consuming crops – corn
• Use chemical fertilizers to avoid having to alternate crops in a given field– Typically use ammonia-based fertilizers
Chapter 16 31
Phosphorus
• Often limiting growth factor in plants
• Used as fertilizer since ancient times
• Historically, produced from bones, guano, or fish meal
• Produced today from phosphate-containing rock– ~90% used for agriculture
Chapter 16 32
Potassium Fertilizer
• Usually abundant
• Produced from various mines around world
• Essential to fluid balance of the cell
Chapter 16 33
Other Essential Elements
Chapter 16 34
War Against Pests
• Insecticides: substances that kill insects
• Pesticides: substances that kill organisms that we consider pests
• Early pesticides contained arsenic
• May have some toxicity to other creatures
Chapter 16 35
DDT: Dream Insecticide
• Easy to produce
• Highly effective
• Did not show toxicity to humans
• Used extensively during World War II– Slowed down spread of malaria, kept lice
population in check – Saves millions of lives
Chapter 16 36
Decline and Fall of DDT
• Overuse led to insects developing resistance to DDT
• Pesticide persistence: substance did not readily break down in environment
• Toxic to fish as well as insects
• Also get biological magnification
Chapter 16 37
Biological Magnification
Chapter 16 38
Biological Insect Controls
• Use natural enemies to get rid of pests• May not be as effective as chemical pesticides• Possible to insert genes that confer pest
resistance• Many ways to do this
– Sterilization– Pheromones– Juvenile hormones
Chapter 16 39
Herbicides and Defoliants
• Herbicides: kill weeds– Allow for more abundant harvests
• Defoliants: cause leaves to fall off plants– Used to help harvest of crops– Example: makes harvesting of cotton
easier
• May see buildup of resistance
Chapter 16 40
Energy Flow of Modern Agriculture
Chapter 16 41
Sustainable Agriculture
• Organic farming uses less energy but requires more labor and produces fewer crops
• Sudden switch to organic farming could be disastrous
Chapter 16 42
Malthusian Mathematics
• Basically said: Population grows faster than food supply; humans must control birthrate
• Arises from difference in arithmetic growth vs. geometric growth
Chapter 16 43
Can We Feed the World?
• Increased food production since Malthus’ time
• Still hungry in this day and age
• Caused by: war, poverty, and lack of arable land
• Modern agriculture dependent on cheap energy