Food Composition

1. Food Composition Chapter 9

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=12354500

3. Food Composition Chemical substances found in the largest amounts in food: Water found inside cells in plants and animals Carbohydrates Fats Protein

4. 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

5. 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

6. 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

7. 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 +

8. 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

9. Carbohydrates Simple sugars Complex starch and fiber Made of Carbon (C) Hydrogen (H) Oxygen (O) One molecule of H2O for each atom of carbon

10. 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

11. Monosaccharides Glucose Fructose Galactose

12. Disaccharides Sucrose Glucose + Fructose Lactose Glucose + Galactose Maltose Glucose + Glucose

13. Oligosaccharides Raffinose and Stachyose Not broken down by digestive tract Found in dried beans

14. 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

15. 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

16. 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

17. Lipids or Fats Insoluble in water Feel “greasy” Three major groups Triglycerides Phospholipids Sterols

18. 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

19. 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

20. 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

21. 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

22. Linoleic Acid An essential fatty acid Cannot be made by the body – must be consumed in food

23. Cis – Trans Configuration Cis Hydrogen atom on both sides of bond Trans Hydrogen atoms on opposite sides of bond

24. Phospholipids Found in food in relatively small amounts Function as emulsifiers One side of molecule attracts fat One side attracts water i.e. Lecithin

25. 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

26. 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

27. Proteins Essential nutrient In food preparation several important roles Binding water Forming gels Thickening Producing foams Aiding browning

28. Protein Contain Carbon Hydrogen Oxygen Nitrogen Potentially also sulfur, phosphorus, iron Large molecules Hundreds or thousands of amino acids joined with peptide linkage

29. Protein Structure Primary Long chains Secondary Springlike coiling - Alpha helix Tertiary Folding of coils forming globular shape Quaternary Combining of globular proteins

30. 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

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

32. Properties and Reactions Buffering Denaturation and Coagulation Enzymes

33. 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

34. Solutions and Dispersions Solutions Colloidal solutions Sol Gel Foams Emulsions Suspensions