Note

 Lecture 22- 6 March 2015

Lipids

Definition Broad range of organic compounds that dissolve in organic solvents such as alcohol, ether, acetone but are much less soluble in water Hydrophobic (lipophilic) vs hydrophilic (lipophobic) Lipids are hydrophobic

Definition continued

Some lipids are more hydrophilic than others (eg phospholipids) The degree of hydrophilicity depends on molecular charge Water is charged Remember that like likes like- what does this mean

Classes of lipids in foods

Fatty acids- chains (of varying length) of carbon with hydrogens and oxygens attached to the carbons

Classes of lipids in foods

-fatty acids are: -saturated (no double bonds)-more in animal

fats

-monounsaturated (one double bond)-olive oil

-omega 9 (eg major monounsaturated in olive

oil)

Classes of lipids in foods

-fatty acids are: -polyunsaturated (2 or more double bonds) more of these in plant oils than animals 

-omega 6 (major polyunsaturated fatty acids in many plant oils)

-omega 3- major polyunsaturated fatty acidsin fish and some plant oils (eg flax,

canola oil)

Classes of lipids in foods

Triglycerides –3 fatty acids attached to glycerol  

-very hydrophobic 

-interestingly glycerol is not very hydrophobic – rather leans toward hydrophilic

 

Classes of lipids in foods Phospholipids- one or 2 fatty acids

attached to a glycerol backbone

-third carbon of glycerol has a phosphate group attached to it

-most famous of these is lecithin 

-somewhat water soluble

Classes of lipids in foodsSterols- molecules made up of rings

- one of the rings can have a fatty acid attached

  -cholesterol is the most famous (infamous?) of these- Michael Brown has described cholesterol as being the most highly decorated little molecule in the world

  -plant sterols = phytosterols 

-sterols are quite hydrophobic

In foods-most of lipid is in the form of triglycerides

 -fats and oils- all triglyceride

 -fats are generally considered to be solid at room temperature

-oils are generally considered to be liquid at room temperature

-though fats are sometimes used interchangeably with oils

In foods 

 - to make an oil more saturated one can bubble

hydrogen gas through it  -unfortunately this produces trans fatty acids-for example in margarine- this makes the margarine solid at room temperature (about 20 degrees celsius) 

In foods

-get cholesterol in foods from

animals and phytosterols in plant foods  

-these are in foods in small amounts (less than triglycerides but more than

phospholipids)  -phospholipids occur in plant and animal

food sources but these are a minor component of our nutritional lipid load

 

Digestion-little chemically in mouth or stomach-

why?

-issue of mechanical digestion 

-small intestine enzymes break down triglycerides and phospholipid generating fatty acids

 -fatty acids and sterols not broken down

further in stomach or intestine butare absorbed whole into small intestinal wall

Absorption

-occurs in small intestine

-absorption of fatty acids and sterols  

-chylomicrons are made in the intestinal wall 

Transport- chylomicrons converted to very low density lipoproteins which are converted to low density lipoproteins

  -all of these conversions

happen in liver 

-high density lipoproteins are made in the liver from various lipids and proteins some of which are left over from liver conversions of lower density lipoproteins

Transport

lipoproteins- lipids cannot be transported easily in the blood (why?) -to overcome this solubility issue must wrap lipids in protein and phospholipid coat to get a lipoprotein -once the lipids are in this coat they are easily transported to where they are needed

Transport

-lipids are used for -energy -fat soluble vitamin transport -building cell membranes

-acting as cellular messengers (one part of the cell telling another part of the cell or other cells what to do and when to do and how much to do it).

-however lipids can also cause problems in the body

-weight problems- arthritis-type II diabetes

-heart disease -stroke -high blood pressure -kidney failure -a number of other problems