Download Chapter 9 Food Composition

Food Composition
Chapter 9
Food Composition



Food contains chemical molecules
Chemical composition may be determined in
laboratory
Tables of food composition available


USDA National Nutrient Database
http://www.ars.usda.gov/main/site_main.htm?modecode=12
354500
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Food Composition

Chemical substances found in the largest amounts in
food:
 Water
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

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found inside cells in plants and animals
Carbohydrates
Fats
Protein
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Water

All foods contain at least some water
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Free water
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Held inside cells
Maintains properties of free water
May be removed by pressure
Bound water
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
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Is part of molecule structure
Reduced mobility
Does not retain properties of free water
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Water Activity
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More bound water, then less water activity
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Water activity
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
Ratio of the vapor pressure of water in a food at a specified
temperature to the vapor pressure of pure water at same
temperature
Foods more perishable if higher water activity
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
Microorganisms need water!
To reduce water activity
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

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Dry
Freeze
Add sugar or salt
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Uses of Water in Food Prep
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Universal solvent
Heat transfer
Freezing
Cleansing agent
Promotion of chemical changes
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Ionization of salt
Baking powder
Water and pH
Hydrolysis reactions
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Nature of Water
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

H2O
Two hydrogen atoms bonded
with covalent bonds to one
oxygen atom
Is dipolar



Negative on oxygen side
Positive on hydrogen sides
Oxygen
Hydrogen bonds
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H+
H+
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Water Hardness

Types of hard water
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Hard water and food preparation
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Temporary
Permanent
Rehydration and softening of dried beans slowed
Alkalinity may affect color of vegetables
Promote cloudiness in tea
Water may be softened
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Carbohydrates

Simple
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Complex
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
sugars
starch and fiber
Made of
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
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Carbon (C)
Hydrogen (H)
Oxygen (O)
One molecule of H2O for each atom of carbon
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Chemical Classification

Classified by number of basic sugar units
linked together
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Monosaccharide – One unit
Disaccharides – Two units
Oligosaccharides – 10 or fewer units
Polysaccharides – Up to 1000 units
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Monosaccharides

Glucose

Fructose
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Galactose
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Disaccharides
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Sucrose
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
Lactose
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
Glucose + Fructose
Glucose + Galactose
Maltose

Glucose + Glucose
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Oligosaccharides

Raffinose and Stachyose

Not broken down by digestive tract

Found in dried beans
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Polysaccharides

Starch
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Amylose
Amylopectin
Dextrins

Produced when starch molecules are partially broken down
by enzymes, acid, or heat.

Less thickening power than starch

Glycogen

Plant Fiber Components
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Plant Fiber Components

Called dietary fiber / roughage / bulk
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Cellulose
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Hemicellulose
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Beta-glucans
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Pectic substances
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Found in oats and barley
Associated with reduced risk of heart disease
Pectin forms gels in jams, jellies, and preserves
Vegetable gums
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Browning of Foods
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Carmelization
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Heating of sugars above melting point
Maillard Reaction

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Involves carbohydrate
Carbonyl group of sugar combines with amino group of a
protein with removal of water. After additional reactions
brown pigments are formed

i.e. browning of bread during baking
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Lipids or Fats

Insoluble in water

Feel “greasy”
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Three major groups
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Triglycerides
Phospholipids
Sterols
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Triglycerides


Account for 90-95 percent of fatty substances
in food.
Composed of

3 fatty acids


linked atoms of carbon with organic acid group
One molecule glycerol

3 carbon atoms and three hydroxyl groups
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Fatty Acids
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
Most fatty acids in foods are combined in
triglycerides.
Fatty acids differ
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Number of hydrogen atoms attached
Length of carbon chain
Carbon chains

Usually even numbered
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Types of Fatty Acids
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Saturated fats
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Unsaturated
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No double bonds between carbon atoms, so no more
hydrogen can be added
Double bonds between some of the carbon atoms that can be
broken to add hydrogen
Monounsaturated

One double bond
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Omega 3 fatty acids

Polyunsaturated fatty acids with double bond
between 3rd and 4th carbon from the left on the
structure.

Found in fatty fish

Protective for heart disease
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Linoleic Acid


An essential fatty acid
Cannot be made by the body – must be
consumed in food
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Cis – Trans Configuration
 Cis


Hydrogen atom on both sides of bond
Trans
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Hydrogen atoms on opposite sides of bond
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Phospholipids

Found in food in relatively small amounts

Function as emulsifiers

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One side of molecule attracts fat
One side attracts water

i.e. Lecithin
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Sterols

Cholesterol
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Widely known sterol
Found ONLY in animal foods
Is associated with coronary heart disease
Our bodies also make cholesterol
Plant sterols


Phytosterols
Interfere with absorption of cholesterol
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Fat in Food Preparation


Tenderizing in baked foods
Contribute to leavening
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Promote moistness
Major components of salad dressings
May be heated to high temperatures

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Creaming of fat and sugar
Frying of foods
Contribute flavor

Butter
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Proteins


Essential nutrient
In food preparation several important roles

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Binding water
Forming gels
Thickening
Producing foams
Aiding browning
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Protein
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Contain

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Carbon
Hydrogen
Oxygen
Nitrogen
Potentially also sulfur, phosphorus, iron
Large molecules

Hundreds or thousands of amino acids joined with peptide
linkage
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Protein Structure
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Primary
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Secondary
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Springlike coiling - Alpha helix
Tertiary
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Long chains
Folding of coils forming globular shape
Quaternary

Combining of globular proteins
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Protein Quality

Amino acids used as
building blocks for proteins
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Nine amino acids are
essential for adult human
nutrition
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Complete proteins include
essential amino acids
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Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
Histidine
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Food Sources

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Meats, Fish, and Poultry
Eggs and Dairy
Nuts
Dry legumes
Cereal grains – in lesser amounts
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Properties and Reactions

Buffering

Denaturation and Coagulation

Enzymes
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Solutions and Dispersions
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Gas dispersed in liquid
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Liquid dispersed in liquid
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Air in whipped egg white
Oil dispersed in vinegar
Solid dispersed in liquid

A protein such as casein dispersed in milk
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Solutions and Dispersions
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Solutions
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Colloidal solutions
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Sol
Gel
Foams
Emulsions
Suspensions
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