Lecture Discovering nutrition - Chapter 4: Carbohydrates: simple sugars and complex chains spotlight on alcohol

Chapter 4
Carbohydrates
: Simple
Sugars and
Complex
Chains


What Are Carbohydrates?
•

•

Sugars, starches, and
fibers
Major food sources:
Plants
–

•

Produced during
photosynthesis

Two main carbohydrate
types
–

Simple (Sugars)

–

Complex (Starches and


Simple Sugars
•

Monosaccharides
–

Glucose

–

Fructose

–

Galactose


Simple Sugars
•

Disaccharides: Consist
of two
monosaccharides
linked together
–

Sucrose

–

Lactose

–

Maltose


Monosaccharides
•

Glucose
–

Most abundant simple sugar in nature

–

Also called dextrose

–

Gives food a mildly sweet flavor

–

Usually joined to another sugar in foods

–

Provides energy to body cells
•

Body closely regulates blood sugar levels


Monosaccharides
•

Fructose
–

Also called levulose or fruit sugar

–

Tastes the sweetest of all the sugars

–

Occurs naturally in fruits and vegetables

–

Found in fruits, honey, and corn syrup

Monosaccharides
•

Galactose
–

Rarely occurs as a monosaccharide in food

–

Usually bonds to glucose to form lactose
•

Primary sugar in milk and dairy products


Disaccharides
•

•

Sucrose: glucose + fructose
–

“Table sugar”

–

Made from sugar cane and sugar beets

–

Listed as sugar on food labels

Lactose: glucose + galactose
–

“Milk sugar”

–

Found in milk and milk products


Disaccharides
•

Maltose: glucose + glucose
–

“Malt sugar”

–

Seldom occurs naturally in foods

–

Product of starch breakdown

–

Found in germinating cereal grains


Complex Carbohydrates
•

Chains of two or more sugar molecules
–

Oligosaccharides
•

•

–

Three to ten sugar molecules
Examples sources: dried beans, peas,
and lentils

Polysaccharides
•

•

Long chains of monosaccharides
Structural differences affect how they
behave in water and with heating

Complex Carbohydrates
•

Starch
–

Plants store energy as starch

–

Found in grains, legumes, and tubers
(potatoes and yams)

–

Long chains of glucose units

–

•

Amylose—straight chains

•

Amylopectin—branched chains

Resistant starch: A starch that is not

digested



Complex Carbohydrates
•

Glycogen
–

Living animals store carbohydrate in the
form of glycogen

–

Provides body glucose when blood
glucose levels get low

–

Highly branched chains of glucose units

–

Most stored in our skeletal muscle and
liver

–

Carbohydrate “loading”

Complex Carbohydrates
•

Fiber
–

Nondigestible carbohydrates and lignins

–

Dietary fiber: Found in plants
•

Fruits, vegetables, legumes, and whole
grains

–

Functional fiber: Isolated and added to
foods

–

Total fiber: Sum of dietary fiber and
functional fiber

Complex Carbohydrates
•

Types of fiber
–

Cellulose
•

–

Hemicelluloses
•

–

Indigestible by humans and a
component of dietary fiber
Variety of monosaccharides with many
branching side chains

Pectins
•

Dietary fiber found in all plants,
especially fruits



Complex Carbohydrates

•

Types of fiber
–

Gums and cilages
•

–

Gel-forming fibers that help hold plant
cells together

Lignins
•

Indigestible substances that make up
woody parts of vegetables and the
seeds of fruits


Complex Carbohydrates
•

Types of fiber
–

Beta-glucans
•

–

Polysaccharides of branched glucose
units

•

Found in barley and oats

•

Help decrease blood cholesterol levels

Chitin and chitosan
•

Primarily consumed in supplement form

•

Marketed as weight-loss supplements


Carbohydrate Digestion and
Absorption
•

Digestion breaks down carbohydrates to
single sugars
–

Mouth
•

–

Salivary amylase begins digestion of
carbohydrates

Stomach
•

Acidity of stomach juices halt action of salivary
amylase and stops carbohydrate digestion


Carbohydrate Digestion and
Absorption
•

Digestion
–

Small intestine
•

Pancreatic amylase continues starch
digestion

•

Brush border enzymes digest disaccharides

•

Other digestive enzymes
–

Maltase, sucrase, and lactase split
maltose, sucrose, and lactose,
respectively


Carbohydrate Digestion and
Absorption
•

Digestion
–

Bonds that link glucose molecules
•

Alpha bonds
–

Broken down by human enzymes
»

•

Starch

Beta bonds
–

Bonds remain unbroken by human
enzymes
»

Cellulose


Carbohydrate Digestion and
Absorption
•

Digestion
•

Enzymes
–

Highly specific
»

•

Examples include lactase and Beano

Some carbohydrates remain intact, such
as fiber and resistant starch



Carbohydrate Digestion and
Absorption
•

Absorption: The small intestine swings into
action
–

–

End products of carbohydrate digestion
•

Glucose

•

Galactose  glucose

•

Fructose  glucose

Liver
•

Stores and releases glucose as need to maintain
blood glucose levels