Transcript Chemistry for Changing Times 11th Edition Hill and Kolb

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.