food composition chapter 9. introductory foods, 13 th ed. bennion and scheule © 2010 pearson higher...

Food Composition

Chapter 9

Introductory Foods, 13th ed.Bennion and Scheule

© 2010 Pearson Higher Education,Upper Saddle River, NJ 07458. • All Rights Reserved.2

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

http://www.ars.usda.gov/main/site_main.htm?modecode=12354500

http://www.ars.usda.gov/main/site_main.htm?modecode=12354500



Food Composition Chemical substances found in the largest amounts in

food: Water

found inside cells in plants and animals Carbohydrates Fats Protein



Water All foods contain at least some water

Free water Held inside cells Maintains properties of free water May be removed by pressure

Bound water Is part of molecule structure Reduced mobility Does not retain properties of free water



Water Activity

More bound water, then less water activity

Water activity 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 Microorganisms need water! To reduce water activity

Dry Freeze Add sugar or salt



Uses of Water in Food Prep Universal solvent Heat transfer Freezing Cleansing agent Promotion of chemical changes

Ionization of salt Baking powder

Water and pH Hydrolysis reactions



Nature of Water H2O Two hydrogen atoms bonded

with covalent bonds to one oxygen atom

Is dipolar Negative on oxygen side Positive on hydrogen sides

Hydrogen bonds

H +

Oxygen

H +



Water Hardness Types of hard water

Temporary Permanent

Hard water and food preparation Rehydration and softening of dried beans slowed Alkalinity may affect color of vegetables Promote cloudiness in tea

Water may be softened



Carbohydrates Simple

sugars

Complex starch and fiber

Made of Carbon (C) Hydrogen (H) Oxygen (O) One molecule of H2O for each atom of carbon



Chemical Classification Classified by number of basic sugar units

linked together Monosaccharide – One unit Disaccharides – Two units Oligosaccharides – 10 or fewer units Polysaccharides – Up to 1000 units



Monosaccharides Glucose

Fructose

Galactose



Disaccharides Sucrose

Glucose + Fructose

Lactose Glucose + Galactose

Maltose Glucose + Glucose



Oligosaccharides Raffinose and Stachyose

Not broken down by digestive tract

Found in dried beans



Polysaccharides Starch

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



Plant Fiber Components

Called dietary fiber / roughage / bulk

Cellulose

Hemicellulose

Beta-glucans Found in oats and barley Associated with reduced risk of heart disease

Pectic substances Pectin forms gels in jams, jellies, and preserves

Vegetable gums



Browning of Foods Carmelization

Heating of sugars above melting point

Maillard Reaction 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



Lipids or Fats Insoluble in water

Feel “greasy”

Three major groups Triglycerides Phospholipids Sterols



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



Fatty Acids Most fatty acids in foods are combined in

triglycerides.

Fatty acids differ Number of hydrogen atoms attached Length of carbon chain

Carbon chains Usually even numbered



Types of Fatty Acids Saturated fats

No double bonds between carbon atoms, so no more hydrogen can be added

Unsaturated Double bonds between some of the carbon atoms that can be

broken to add hydrogen Monounsaturated

One double bond



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



Linoleic Acid

An essential fatty acid

Cannot be made by the body – must be consumed in food



Cis – Trans Configuration Cis

Hydrogen atom on both sides of bond

Trans Hydrogen atoms on opposite sides of bond



Phospholipids Found in food in relatively small amounts

Function as emulsifiers One side of molecule attracts fat One side attracts water

i.e. Lecithin



Sterols Cholesterol

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



Fat in Food Preparation Tenderizing in baked foods Contribute to leavening

Creaming of fat and sugar Promote moistness Major components of salad dressings May be heated to high temperatures

Frying of foods Contribute flavor

Butter



Proteins Essential nutrient In food preparation several important roles

Binding water Forming gels Thickening Producing foams Aiding browning



Protein Contain

Carbon Hydrogen Oxygen Nitrogen Potentially also sulfur, phosphorus, iron

Large molecules Hundreds or thousands of amino acids joined with peptide

linkage



Protein Structure Primary

Long chains Secondary

Springlike coiling - Alpha helix Tertiary

Folding of coils forming globular shape Quaternary

Combining of globular proteins



Protein Quality Amino acids used as

building blocks for proteins

Nine amino acids are essential for adult human nutrition

Complete proteins include essential amino acids

Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Histidine



Food Sources Meats, Fish, and Poultry Eggs and Dairy Nuts Dry legumes Cereal grains – in lesser amounts



Properties and Reactions Buffering

Denaturation and Coagulation

Enzymes



Solutions and Dispersions Gas dispersed in liquid

Air in whipped egg white

Liquid dispersed in liquid Oil dispersed in vinegar

Solid dispersed in liquid A protein such as casein dispersed in milk



Solutions and Dispersions Solutions

Colloidal solutions Sol Gel Foams Emulsions

Suspensions

food composition chapter 9. introductory foods, 13 th ed. bennion and scheule © 2010 pearson higher...

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