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The Lipids
TriglyceridesPhospholipids
Sterols
Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning
Lipids (C,H,O)• Triglycerides (Neutral lipids)
– Fats and oils• 95% of the lipids in food• 99% of the lipids stored in the body• Fats – solid at room temperature (70F or
25C)• Oils – liquid at room temperature
• Phospholipids• Sterols• Lipids include the fat soluble vitamins
Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning
Fatty Acids and Triglycerides
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• Triglycerides are made up of– Glycerol– Fatty acids
Glycerol
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Condensation of Glycerol & Fatty Acids to Form a Triglyceride
Fatty Acids and Triglycerides
• glycerol + 3 fatty acids triglyceride + H2O
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Fatty Acids• Fatty acids
– Fatty acids are long unbranched chains of carbon atoms with attached hydrogens and other groups.
– A carboxyl (-COOH) group at one end gives the molecule its acidic properties.
– Most naturally occurring fatty acids contain an even number of carbon atoms in their backbone chains. (Few with odd numbers are found in all organisms, but they are a minor fraction of the total)
– Length• Various lengths most important are 12-24• Tables C-1 and C-2 in Appendix C
– Saturated vs. unsaturated
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Fatty Acids• Fatty acids
– Length•Various lengths - most important are
12-24•Except for butyric and caproic (4 and
6 carbons) longer lengths (18 and above) are characteristic of animal fats.
•Length affects softness (see later)•Tables C-1 and C-2 in Appendix C
– Saturated vs. unsaturated
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Fatty Acids
• Organic acids– Example: acetic acid
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Fatty Acids
• Length of carbon chain
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Stearic acid – 18-carbon, saturated
Simplified structure
Fatty Acids• Degree of saturation
– Saturated fatty acid• Has all the Hydrogen needed to satisfy all
four bonds of each carbon– Monounsaturated fatty acid
• Has two hydrogens less causing a double bond to form
– Polyunsaturated fatty acid• Has four or more hydrogens less causing two
or more double bonds• Point of saturation
– Location of the double bonds (see below)
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An impossible chemical structure
Oleic acid – 18-carbon, monounsaturated
Linoleic acid – 18-carbon, polyunsaturated
Fatty Acids• Location of double bonds
– Omega number•Omega-3 fatty acid•Omega-6 fatty acid
Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning
Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning
Omega-3 and Omega-6 Fatty Acids Compared
A Mixed Triglyceride
This mixed triglyceride includes a saturated fatty acid, a mono-unsaturated fatty acid, and a polyunsaturated fatty acid.
Triglycerides• Degree of unsaturation revisited
– Firmness• Polyunsaturated fats are liquids at
room temperature• Many animal fats are saturated
e.g. butter• There are plant oils that are
saturated e.g. coconut oil, palm oil, cocoa butter (tropical oils)
• But these tend to have shorter carbon chains so they are softer than animal fats (longer chain lengths)
• Saturated and unsaturated fatty acids contents of various foods – See Appendix H
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Triglycerides• Degree of unsaturation revisited
– Stability•Oxidation
– Exposure to oxygen breaks down all fats (rancidity)
– Double bonds are unstable– More saturated fats are more stable– Saturated>Monounsaturated>Polyunsaturated
•Methods to overcome oxidation–Seal in airtight, nonmetallic
containers, protect from light, refrigerate
– Add Antioxidants– Hydrogenation
Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning
Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning
Triglycerides• Degree of unsaturation revisited
– Hydrogenation•Makes fats more stable•Makes food taste better (pie crusts
and puddings)–Cis vs. trans-fatty acids
•Trans-fatty acids behave more like saturated fatty acids in the body
Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning
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Hydrogenation
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Cis- and Trans-Fatty Acids Compared
Phospholipids
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Lipids• Hydrophobic vs. hydrophilic
– For something to be soluble in water (and therefore hydrophilic) it must have a charge
– Fatty acids and triglycerides don’t have any charges (hence the name neutral lipids)
– Phospholipids have charge from the phosphate group so they have a hydrophilic end and a hydrophobic end
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