Transcript Chapter 16 Food: Those Incredible Edible Chemicals

Chapter 16
Food: Those Incredible Edible
Chemicals
Food
• Three main classes:
– Carbohydrates
– Fats
– Proteins
• Also need:
– Water
– Fiber
– Vitamins
– Minerals
Chapter 16
2
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
3
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
4
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
5
Chapter 16
6
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
7
Lipoprotein
• Group of proteins combined with a lipid
– typically triglycerides and cholesterol
• Classified according to density
Chapter 16
8
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
9
Chapter 16
10
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
11
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
12
Chapter 16
13
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
14
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
15
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
16
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
17
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
18
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
19
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
20
Artificial Sweeteners
• Developed to help combat obesity
• Tend to be polyhydroxy compounds
• Varying amounts of sweetening ability
Chapter 16
21
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
22
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
23
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
24
Poisons in Food
• Some are natural
– Botulism toxin
– Oxalic acid
– Aflatoxins
• Some cause cancer
– Aflatoxins
• Some are toxic
– Botulism toxin
Chapter 16
25
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
26
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
27
Growing Food
Chapter 16
28
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
29
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
30
Phosphorus
• Often limiting growth factor in plants
• Used as fertilizer since ancient times
• Historically, produced from bones,
guano, or fish meal
• Produced today from phosphatecontaining rock
– ~90% used for agriculture
Chapter 16
31
Potassium Fertilizer
• Usually abundant
• Produced from various mines around
world
• Essential to fluid balance of the cell
Chapter 16
32
Other Essential Elements
Chapter 16
33
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
34
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
35
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
36
Biological Magnification
Chapter 16
37
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
38
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
39
Energy Flow of Modern Agriculture
Chapter 16
40
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
41
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
42
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
Chapter 16
43