CARBOHYDRATES
• Sources, Classification, Functions and Recommended Dietary Allowance of
Carbohydrates. Glycemic index. Artificial Sweetening Agents
• Effect of Cooking on Carbohydrates and Storage of Carbohydrates
FUNCTIONS OF CARBOHYDRATES
• Provide energy
• Spare proteins
• Assist in the breakdown of fats
• Gives Bulk to the diet
PROVIDE ENERGY •
They are used as material for energy storage and production. • Starch
and glycogen, respectively in plants and animals, are stored
carbohydrates from which glucose can be mobilized for energy
production.
• Glucose can supply energy both fuelling ATP synthesis. • It should be
noted that glucose, used as energy source, “burns” without yielding
metabolic wastes, being turned in CO2and water, and of course
releasing energy.
• Monosaccharides supply 3.74 kcal/g, disaccharides 3.95 kcal/g, while
starch 4.18 kcal/g; on average it is approached to 4 kcal/g.
PROTEIN SAVING ACTION
• They exert a protein-saving action: if present in adequate amount in
daily nourishment, the body does not utilize proteins for energy
purpose.
• If needed, the body can use proteins as an energy source but the
body is less efficient in using proteins
• If very little carbohydrates is consumed, the body will use proteins for
its major functions.
• By eating adequate amounts of carbohydrates, the proteins are
spared and allowed to be used for their more vital roles.
BREAKDOWN OF FATS
• Their presence is necessary for the normal lipid metabolism. • More than
100 years ago Pasteur said: “Fats burn in the fire of carbohydrates“. This idea
continues to receive confirmation from the recent scientific studies.
• Moreover, excess carbohydrates may be converted in fatty acids and
triglycerides (processes that occur mostly in the liver).
• If the diet is too low in carbohydrates, the body cannot completely break
down fats.
• Incompletely broken down fats form compounds called ketone bodies. •
Ketone bodies collect in the blood stream and become acidic—causing
damage to cells and organs (ketosis).
ADDS BULK TO THE DIET
• Fibre helps promote normal digestion and elimination of body
wastes • Fibre swells and makes you feel full
• Fibre also slows the rate at which the stomach
empties • It also:
✔Prevents appendicitis
✔Decreases risk of heart and artery disease
✔Lowers risk of colon cancer
✔Controls diabetes
DIETARY FIBRE
• Fibre is a type of carbohydrate that the body can’t digest.
• Though most carbohydrates are broken down into sugar molecules,
fibre cannot be broken down into sugar molecules, and instead it
passes through the body undigested.
• Fibre helps regulate the body’s use of sugars, helping to keep hunger
and blood sugar in check.
• There are two types - soluble and insoluble fibre
TYPES OF FIBRE
• Soluble fibre - which dissolves in water, can help lower glucose levels
as well as help lower blood cholesterol.
• Foods with soluble fibre include oatmeal, nuts, beans, lentils, apples
and blueberries.
• Insoluble fibre - which does not dissolve in water, can help food move
through your digestive system, promoting regularity and helping
prevent constipation.
• Foods with insoluble fibres include wheat, whole wheat bread, whole
grain couscous, brown rice, legumes, carrots, cucumbers and
tomatoes.
OTHER FUNCTIONS OF CARBOHYDRATES
• Glucose is indispensable for the maintenance of the integrity of
nervous tissue (some central nervous system areas are able to use
only glucose for energy production) and red blood cells.
• Two sugars, ribose and deoxyribose, are part of the bearing structure,
respectively of the RNA and DNA and obviously find themselves in the
nucleotide structure as well.
• Two homopolysaccharides, cellulose (the most abundant
polysaccharide in nature) and chitin (probably, next to cellulose, the
second most abundant polysaccharide in nature), serve as structural
elements, respectively, in plant cell walls and exoskeletons of nearly a
million species of arthropods (e.g. insects, lobsters, and crabs).
FUNCTIONS OF CARBOHYDRATES
• Heteropolysaccharides provide extracellular support for organisms of
all kingdoms: They hold individual cells together and provide
protection, support, and shape to cells, tissues, and organs.
TOO MUCH CARBOHYDRATES
• Dental carries/cavities - Sticky carbohydrate foods like raisins, cookies,
crackers and caramels tend to cling to teeth and cause tooth decay
• Weight gain - Sugars and starches you eat are converted to glucose in
the bloodstream and stored in the liver as glycogen. The liver can only
store a limited amount of glycogen. When you consume more
carbohydrate than the liver can store, it is converted to fat. The body
can store an unlimited amount of fat.
TOO LITTLE CARBOHYDRATES
• Ketosis - Associated with low carbohydrate diets
• Glucose is the preferred source of energy. When that is not available,
the body begins to draw on fat stores for energy
• Symptoms include:
Tiredness, headache, feeling thirsty all the time, bad breath,
metallic taste in the mouth, weakness, dizziness, nausea or stomach
ache, sleep problems
STORAGE OF CARBOHYDRATES
• Carbohydrates are the body's preferred
energy source.
• Eating carbohydrates provides energy to
your muscles, brain and nervous system;
facilitates the metabolism of fat; and
ensures that the protein in your muscles
is not broken down to supply energy.
• Since carbohydrates are so important to
your body's function, any excess carbs you
eat will be stored in your liver and
muscles.
• The body stores the excess carbohydrates,
as a compound called glycogen.
GLYCOGEN
• When the body digests complex
carbohydrates, it breaks those
compounds down into a sugar known
as glucose, which the body
metabolizes for energy.
• Any glucose in the bloodstream
remaining after immediate needs for
energy becomes the compound
glycogen, a long chain of linked
glucose molecules, which the body can
later break down again for energy.
LIVER GLYCOGEN STORAGE
• The liver and skeletal muscle in the
body mainly store glycogen.
• Glycogen accounts for approximately
10 percent of the weight of the liver,
while it represents two percent of the
weight of muscles.
• The liver can hold up to about 90 to
110 grams of glycogen and this is used
to maintain blood sugar levels and
energy levels.
MUSCLE GLYCOGEN STORAGE
• Muscles account for 20 percent to 30
percent of the total mass and therefore
provide storage for a larger total amount
of glycogen than the liver does.
• A healthy adult who is well-nourished
can have about 400 grams of muscle
glycogen.
• Your muscles are the secondary storage
facility, filling up only when the liver has
reached its storage capacity.
• Muscle glycogen is used for energy
during prolonged strenuous activity.
GLYCOGEN USE
• When the body can't meet its energy needs with the amount of
glucose circulating in the body, it uses glycogen.
• Under these conditions, the body breaks the stored glycogen down in
order to satisfy those needs.
• Glycogen stored in muscle tissue provides energy to that specific
muscle; for instance, glycogen stored in the legs could provide energy
for running.
• Glycogen stored in the liver regulates the amount of blood glucose as
a whole, ensuring all bodily cells achieve their energy requirements.
STORAGE OF CARBOHYDRATES
• The liver and muscles can store around 500 grams of total
carbohydrate as glycogen.
• If the body has met its immediate energy needs and all glycogen
stores in the body are full, it converts any remaining glucose in the
bloodstream to fat.
• If your intake exceeds the amount required to fill your liver and
muscle tissue, your liver will convert the excess carbohydrate into
glucose and release it into the bloodstream.
STORAGE OF CARBOHYDRATES
• At this point, insulin released from the pancreas will signal to your fat
cells to take up the excess glucose and store it for future use.
• Fat is a much less efficient fuel source than glycogen, because
glycogen is readily available to muscles and is easily broken down into
glucose.
• The body can break fat down and convert it back into glucose for
energy, but only under conditions where glycogen isn't available.
EFFECT OF COOKING ON
CARBOHYDRATES
BROWNING
• There are two main types of browning of foods: enzymatic & non
enzymatic browning. • Enzymic browning – browning of apples and
bananas. • Non-enzymatic browning can again be split in two types: the
Maillard reaction and caramelization.
• Caramellization requires high temperatures (above roughly 150°C)
and only requires the presence of enough sugar.
• The Maillard reaction on the other hand can take place at room
temperature and requires two types of molecules to occur: both
protein and sugars.
CARAMELIZATION • There are many changes that
take place when food is exposed to heat, a process known more
commonly as "cooking.“
• Carbohydrates, the sugars found in starches and in fruits and
vegetables, turn golden brown and form new flavours.
• This transformation is called caramelization, and indeed it is literally
the process that causes sugar to turn into caramel.
• Caramelization in turn is caused by pyrolysis, which is a broad
category of changes that a substance undergoes when exposed to
certain temperatures.
CARAMELIZATION
• Caramelization is the browning of sugars through exposure to heat.
• The most common form of sugar—table sugar or sucrose—is a
disaccharide, a combination of two monosaccharides: glucose and
fructose.
• The two sugars can be easily separated using the enzyme invertase,
which is essentially what bees do when they make honey from nectar.
• Fructose caramelizes more readily than glucose, so baked goods
made from honey are generally a bit darker than those made with
sucrose.
CARAMELIZATION
• When sugar syrups are heated, they pass through several distinct stages,
each having characteristics that are very useful to confectioners.
• Different sugars reach these stages at varying temperatures.
• Caramelization of sugar begins around 310°F. When it reaches the light
caramel stage (at 356°F for sucrose), many complex chemical reactions
change simple sugars into a host of different flavouring compounds.
• Scissions (the breaking of long molecular chains into shorter segments),
rearrangements of molecular components, and subsequent reactions
between the resulting new compounds all occur in rapid succession.
CARAMELIZATION • One of the compounds created
during caramelization is biacetyl (C4H6O2), which has a warm buttery
scent, but there are also traces of as many as one hundred sweet, sour,
and bitter compounds.
• The complexity of the resulting mixture makes the flavour of
butterscotch more interesting than the mere sweetness of sugar.
• A number of yellow and brown water-soluble polymers are also
produced, which accounts for caramel's colouration.
• These polymers are often used as colourants in commercial food
products, from colas to soy sauce, and even in the variety of
pumpernickel known as "black bread."
Stages in the caramelization of sugar
Characteristics and uses
Stage Temperatur e
212˚F Sugar is melted and impurities
rise to the surface.
All water evaporated
Small Thread 215˚F No colour; cools soft; no flavour change. Used in buttercream
frostings.
Large Thread 219˚F No colour; cools soft; no flavour change. Used in preserves.
Small Ball 230–240˚F No colour; cools semisoft; no flavour change. Used in cream
candy fillings, Italian meringue, fondants, fudge,
and marshmallows.
Large Ball 246–252˚F No colour; cools firm; no flavour change. Used in soft
caramels.
Light Crack 264˚F No colour; cools firm; no flavour change. Used in taffy.
Hard Crack 300–331˚F No colour; cools hard; no flavour change. Used in butterscotch
and hard candies.
Extrahard Crack 334˚F Slight colour; shatters like glass when cooled; no flavour
change. Used in nut brittles and hard candies.
Light Caramel 356˚F Pale amber to golden brown; rich flavour. Medium
Caramel 356–370˚F Golden brown to chestnut brown; rich flavour.
Dark Caramel 370–400˚F Very dark and bitter; smells burned. May be used for colouring,
but has little sweetness left.
Black Jack 410˚F Known to Carême as "monkey's blood." At this point, the sugar begins
to breaks down to pure carbon
CARAMELIZATION OF OTHER SUGARS
Sugar Temperature
• Fructose 110° C, 230° F
• Galactose 160° C, 320° F
• Glucose 160° C, 320° F
• Maltose 180° C, 356° F
• Sucrose 160° C, 320° F
MAILLARD REACTION
• The Maillard reaction is a chemical reaction between amino acids and
reducing sugars that gives browned food its distinctive flavour.
• The Maillard reaction is a culinary phenomenon that occurs when
proteins in meat are heated to temperatures of 310 F or higher,
causing them to turn brown.
• Named for the French chemist Louis-Camille Maillard who discovered
the process at the start of the 20th century, the Maillard reaction is
similar to the process of caramelization, where carbohydrates like
sugar turn brown when heated.
Examples of Maillard Reaction
• Seared steaks, pan-fried dumplings, cookies and other kinds of
biscuits, breads, toasted marshmallows, as well as many other foods,
undergo this reaction.
• The reaction is a form of non-enzymatic browning which typically
proceeds rapidly from around 140 to 165 °C (280 to 330 °F). At higher
temperatures, caramelization and subsequently pyrolysis become
more pronounced.
• The reactive carbonyl group of the sugar reacts with the nucleophilic
amino group of the amino acid, and forms a complex mixture of
poorly characterized molecules responsible for a range of aromas and
flavors.
• In the process, hundreds of different flavor compounds are created.
These compounds, in turn, break down to form yet more new flavor
compounds, and so on. Each type of food has a very distinctive set of
flavor compounds that are formed during the Maillard reaction. It is
these same compounds that flavor scientists have used over the years
to make artificial
flavors.
GELATINIZATION
• Starch gelatinization
is the process where
starch and water are
subjected to heat
causing the starch
granules to swell.
• As a result, the water
is gradually absorbed
in an irreversible
manner.
• This gives the system a viscous and transparent
texture.
• The result of the reaction is a gel, which is used
in sauces, puddings, creams and other food
products, providing a pleasing texture.
PROCESS OF GELATINIZATION
• During heating, water is first absorbed in the amorphous space of
starch, which leads to a swelling phenomenon.
• Water then enters via amorphous regions the tightly bound areas of
double helical structures of amylopectin.
• Heat causes such regions to become diffuse, the amylose chains begin
to dissolve, to separate into an amorphous form and the number and
size of crystalline regions decreases.
• Penetration of water thus increases the randomness in the starch
granule structure, and causes swelling, eventually amylose molecules
leach into the surrounding water and the granule structure
disintegrates.
GELATINIZATION
• The most common example to
explain this phenomenon is
pasta
preparation: pasta is
made ​mostly of semolina wheat
(wheat flour) that contains high
amounts of starch.
• When it is cooked in boiling
water, the size increases because
it absorbs water and it gets a soft
texture.
QUIZ ON CARBOHYDRATES
What is not a type of carbohydrate?
• Fat
• Fibre
• Starch
• Sugar
Carbohydrates are the largest part of a healthy diet.
• True
• False
Which is not a chemical element needed to build sugars?
• Carbon
• Oxygen
• Nitrogen
• Hydrogen
Which foods do not contain natural sugar?
• apple
• milk
• strawberry
• All of the above
Which health problems is a consequence of eating too much added
sugar?
• overweight
• heart disease
• diabetes
• all of the above
Why does the body need carbohydrates?
• They provide fuel for the body.
• They're the primary energy source for the brain.
• They prevent the body from having to use protein and fat for
energy. • All of the above
Which of these foods contain carbs?
• Vegetables
• Grains
• Legumes
• All of the above
Which of these carbohydrate-containing food groups impacts your
blood sugar the most quickly?
• Leafy greens
• Vegetables
• Fruits
Which of these foods has refined carbohydrates?
• White flour
• Regular pasta
• Table sugar
• All of the above
How do refined carbohydrates affect the body?
• Break down quickly so you're left feeling hungry
faster • Increase insulin levels and blood pressure •
Both
What is a complex carbohydrate?
• Carbohydrates in their natural, unrefined forms
• Carbohydrates that have been stripped of much of their nutrients
• Tick the row that includes carbohydrate containing food.
• bread, pasta, potatoes, lollies
• beans, pasta, white sugar, fish
• buns, eggs, tomatoes, meat
• cheese, oranges, biscuits, vegetables
True or false: As part of a balanced diet, complex carbohydrates can
help you lose weight.
• TRUE
• FALSE
About how many carbohydrates do you need in a day?
• 50 grams
• 100 grams
• 130 grams
• None of the above
How much of your total daily calorie intake should come from
carbohydrates?
• 10 to 20 percent
• 25 to 40 percent
• 45 to 65 percent
• 90 percent or more
___________ is sugar found in fruit, honey and vegetables.
• Maltose
• Lactose
• Fructose
• Sucrose
When choosing carbohydrates, choose ones low in added
___________.
• Fibre
• Sugar
• Fat
• Vitamins
To stay healthy, you should eat more simple carbohydrates than
complex carbohydrates
• True
• False