The Lipids Triglycerides Phospholipids Sterols Copyright 2005 Wadsworth Group, a division of Thomson Learning

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


Fatty Acids and Triglycerides


• Triglycerides are made up of– Glycerol– Fatty acids

Glycerol


Condensation of Glycerol & Fatty Acids to Form a Triglyceride

Fatty Acids and Triglycerides

• glycerol + 3 fatty acids triglyceride + H2O


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


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


Fatty Acids

• Organic acids– Example: acetic acid


Fatty Acids

• Length of carbon chain


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)



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



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



– 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




– 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



Hydrogenation


Cis- and Trans-Fatty Acids Compared

Phospholipids


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


Phospholipids• Phospholipids in

foods

• Roles of phospholipids– Plasma

membrane– Emulsifiers


Documents

The Lipids Triglycerides Phospholipids Sterols Copyright 2005 Wadsworth Group, a division of Thomson Learning