Carbohydrates
Chapter 15
What Are Carbohydrates?
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Carbohydrate = an organic compound
that is the body’s main source of energy.
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Made up of two main elements carbon and
hydrogen
Carbohydrates are found mainly in foods from
plant sources, such as fruits, vegetables, grain
products, dry beans and peas
Carbohydrates consist of simple and complex
carbohydrates
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Simple carbohydrates consist of one or two sugars
in very small molecules
Complex carbohydrates, which are starches and
fiber, are very large molecules
How Carbohydrates Form
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Carbohydrates are produced by green plants.
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Using the sun’s energy, plants convert carbon
dioxide and water into glucose and oxygen. The
carbon dioxide comes from the air, and water is
taken up by a plant’s roots, known as
photosynthesis.
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The green pigment for photosynthesis to occur is called
chlorophyll.
Glucose = basic sugar molecule from which all
other carbohydrates are built
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A plant can convert glucose molecules into other
sugars, starches, and fiber.
It usually starts by changing glucose into other
sugars, these become starches.
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Green peas from a young plant taste sweeter, than peas
from an older one because they are high in simple
carbohydrates, or sugar.
Peas from an older plant contain a higher level of starch
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Simple Carbohydrates: Sugars
Simple carbohydrates or sugars, are a natural part of
many food.
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Ex. Pineapple and oranges have a sweet taste
Foods with naturally occurring sugars often contain other
nutrients too. Sugars can also be extracted from plants
and used to sweeten food.
The basic sugar molecule is a six-sided ring made of 6
carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.
Hydroxyl group = combination of hydrogen and
oxygen, containing one atom of each element.
Saccharide = is simply a sugar or a substance made
from sugar. (sugars have the following 2 basic molecular
structure)
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Monosaccharide (single sugars) – including glucose, the
“building block” of all other sugars – (fructose, galactose –
natural sugars found in food)
Disaccharides (sugars made up of 2 monosaccharide's
bonded together) – include sucrose which is made up of
glucose and fructose, lactose – found in milk composed of
glucose and galactose, maltose occurs in cereals and
sprouting grains
Properties of Sugar - Sweetness
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Sugars differ in amount of sweetness
 Fructose is generally found sweetest.
 Sucrose, glucose, galactose, maltose, and
lactose follow in decreasing order of
sweetness
 Honey is an example of a very sweet sugar –
when bees make honey, they collect nectar
from flowers that contain fructose, glucose
and sucrose. An enzyme in their body
converts most of the sucrose into fructose and
glucose – this makes honey a highly
concentrated solution of two of the sweetest
sugars.
 Hot and cold also affects the sweetness of
sugar ex. Fructose is generally sweeter in cold
foods
Properties of Sugar - Caramelization

Caramelization = the browning
reaction that can occur with any
kind of sugar
As sugar is heated, some of the water
leaves its molecules in the form of
hydrogen and oxygen. The new
molecules have a higher concentration of
carbon, creating the distinctive caramel
color
 Sucrose, galactose, and glucose all
caramelize at 170°C.
 Fructose on the other hand, caramelizes
at 110°C
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Properties of Sugar – Solubility
(ability to dissolve)
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Sugars are highly soluble in water
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Fructose most soluble in water followed by:
Sucrose
Glucose
Glalactose
Maltose
Lactose
Water temperature affects solubility of sugar
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25°C the solubility of sucrose is 211g per 100g of
water
However if you want to dissolve larger quantities of
sugar, you need to increase the waters temperature
Supersaturated = the solution contains more
dissolved solute than it would normally hold at that
temperature. ( meaning add sugar to hot water, than
cooling the water down, without stirring results in
sugar water)
Properties of Sugar - Crystallization
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Water evaporates, increasing the
concentration of sugar in the solvent.
When sugar reaches a certain
concentration, crystallization occurs
Crystallization from a supersaturated
solution begins when particles enter the
solution (anything even dust)
 The size of the crystals depends on how
many particles are present and how
quickly the crystals grow around them
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Complex Carbohydrates:
Starch and Fiber
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When people talk about starch and fiber
in the diet, they’re speaking of complex
carbohydrates
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Both are found in dry beans, peas and lentils,
potatoes, corn, rice pasta and breads.
Simple carbohydrates have one or two
monosaccharides per molecule
Complex carbohydrates, glucose forms
compounds called polysaccharides.
Polysaccharides is an example of a
polymer
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Polymer = large molecule formed when small
molecules of the same kind chain together
Structure of Starches
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Starches are literally plant food, starches are
stored in granular form, largely in the seeds
and roots
A single molecule of starch can include
anywhere from 400 to several hundred
thousand alpha-D-glucose (form of glucose)
Starch molecules can have two structures:
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Amylose = molecules are linear; they're long
and narrow like a line
Amylopectin = have multiple branches, like the
veins in a leaf
Structure of Fiber/Carbohydrates
in the Body
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The main plant fiber found in food is
cellulose, a polymer made of a form of
glucose called betaD-glucose
Other basic structures of edible fiber
include hemicellulose, pectins, and algal
polysaccharides
Carbohydrates in the Body
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55-65% of your daily calories
should come from carbohydrates,
mostly complex (300g)
Glucose is the main carbohydrate
found in blood
Hydrolysis of Sugars
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Hydrolysis = splitting of a
compound into smaller parts by the
addition of water
This reaction breaks down carbohydrates
until they yield the sugars from which
they are formed
 Hydrolysis of sugars results from the
action of enzymes, certain proteins that
control chemical activities
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Blood Glucose Levels
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The pancreas monitors the flow of
glucose to the cells.
During digestion, the pancreas secretes
the hormone insulin
 Hormone = a chemical messenger that
affects a specific organ or tissue and
brings forth a specific response
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Insulin also helps keep glucose in the blood
at a normal level
If blood glucose is too high, insulin triggers
the liver and muscle cells to remove glucose
from the blood and store it as glycogen.
Questions
1.
2.
3.
4.
5.
6.
How is the term “carbohydrate” related
to the nutrient’s composition?
How are carbohydrates involved in
transferring solar energy to people?
Compare monosaccharides and
disaccharides, using examples to
illustrate.
In developing a new recipe, why might
you use fructose instead of sucrose?
How would a chemist describe a complex
carbohydrate?
What would happen if carbohydrates in
your body were not hydrolyzed.
Questions Continued
7.
8.
9.
10.
11.
12.
Describe the process that ensures your
body a steady flow of glucose.
Compare the complications of Type 1
and Type 2 diabetes.
What is nutritionally significant about
fiber?
Suppose you forgot to calibrate your
thermometer before making candy. It
registers 10°C less than the actual
temperature of the syrup. What may
result?
How do amylose and amylopectin affect
thickening?
Why do food scientists modify starches
for food production?