• Triglycerides are a form of lipid, made up of one molecule of?glycerol?with three?fatty acids?attached to it
• These fatty acids have?long hydrocarbon ‘tails’
• Fatty acids occur in?two?forms:
  • Saturated?fatty acids
  • Unsaturated?fatty acids
    • Unsaturated fatty acids can be?monounsaturated?or?polyunsaturated
• The difference between these fatty acid types is found in their hydrocarbon tails

Saturated fatty acids

• In saturated fatty acids, the bonds between the carbon atoms in the hydrocarbon tail are?all single bonds
• The fatty acid is said to be?‘saturated’ with hydrogen
  • This means that each carbon atom in the hydrocarbon tail (except for the final carbon atom) is bonded to?two hydrogen atoms
• Saturated fatty acids can be?synthesised industrially?by?hydrogenation?(reaction with hydrogen gas) of unsaturated fatty acids
• All the carbon-to-carbon bonds are?single bonds?in saturated fatty acids

An example of a saturated fatty acid

Unsaturated fatty acids

• In unsaturated fatty acids, the bonds between the carbon atoms in the hydrocarbon tail are?not all single bonds
  • There is?at least one carbon-carbon double bond; a fatty acid with one C=C double bond is known as?monounsaturated?fatty acid
  • In some unsaturated fatty acids, there are?many?carbon-carbon double bonds; these are known as?polyunsaturated?fatty acids
  • These double bonds can cause the hydrocarbon tail of unsaturated fatty acids to?kink?(bend slightly), meaning they are?not as straight as saturated fatty acids
• The fatty acid is said to be?‘unsaturated’?because the hydrocarbon tail?does not contain the maximum number of hydrogen atoms?possible
  • This is because each carbon atom in a carbon-carbon double bond?can only bond to one hydrogen atom?(instead of two)

An example of a monounsaturated fatty acid

An example of a polyunsaturated fatty acid

The different isomers of unsaturated fatty acids

• A single C-C bond in a hydrocarbon chain is able to?rotate along its axis so?that rotation of one part of the molecule in relation to others is possible
• The rotation may cause?conformational changes?in molecules but they all remain?identical
• However, when there is a?C=C double bond?in a hydrocarbon chain,?no rotation?is possible
• This causes?isomers?of fatty acids to be formed, each with different properties
• The isomers are labelled?cis?and?trans?isomers

Cis-isomers

• At a C=C double bond, the attached hydrogen atoms are on the?same side?of the hydrocarbon chain as each other
  • This causes a?kink in the fatty acid chain?which means the fatty acid chains are less tightly packed together,?lowering their melting point?(less kinetic energy is needed to break them apart)
  • Triglycerides that contain cis-unsaturated fatty acids are?liquid?(oils) at room temperature

The Structural Differences Between a Saturated and a Cis-Unsaturated Fatty Acid

Trans-isomers

• At a C=C double bond, the attached hydrogen atoms are on the?opposite sides?of the hydrocarbon chain to each other
  • The lack of bend in the hydrocarbon chain allows them to pack more closely together meaning they have a?higher melting point?(this property makes them more attractive to food manufacturers)
  • Triglycerides that contain trans-saturated fatty acids are?solid?are room temperature

The Structure of a Trans-Unsaturated Fatty Acid

The use of trans-fatty acids in the food industry

• Trans-fatty acids occur in small quantities in natural products such as?dairy?and?red meat
• Artificial trans-fats (which contain trans-fatty acids) are made industrially by the?hydrogenation?of liquid vegetable oils
• Trans-fats are?favoured by food manufacturers?for commercial reasons
  • They are more?solid at room temperature
  • They create?more stable emulsions?in shortening agents
  • Food products with trans-fats appear (in their retail packaging)?drier?and?less 'greasy'?to consumers
  • Alleged?taste?benefits (though this is subjective)
  • They can be?reused?more times eg. in large-scale deep-fat fryers
  • Many countries have?legislated to restrict the use of trans-fats?in the foodservice industry
• Many foods that contains trans-fats (often labelled as 'partially hydrogenated vegetable oils') are sold as processed products in supermarkets
  • Biscuits/cookies
  • Cakes
  • Doughnuts
  • Pie crusts
  • Crisps
  • Pizza bases
  • Certain kinds of margarine and spreads

Trans-fatty acids have associated health risks

• The two types of fat that lead to health problems are namely?saturated fats?and?trans-fats
  • Doctors recommend limiting your intake of these types of fats
• Trans-fats alter the balance of various types of cholesterol
  • They?increase low-density lipoprotein (LDL)?levels in circulation (so-called 'bad' cholesterol)
  • They?decrease high-density lipoprotein (HDL)?levels in circulation (so-called 'good' cholesterol)
• LDLs are known?to increase the risk of coronary heart disease, blood clotting and strokes
• Doctors recommend that the bulk of fats intake should come from?monounsaturated fats, which?reduce?LDL levels
  • Omega-3 fats and oils are a well-publicised source of monounsaturated fats; these are found in fish, pulses and certain nuts

Excess consumption of trans-fatty acids and saturated fats can lead to the buildup of cholesterol and the blockage of coronary arteries, causing Coronary Heart Disease (CHD)

Evaluating claims

• Evidence for the claims surrounding the health risks associated with trans-fats often comes from 'cohort studies'
  • Eg. Greenland Eskimos, whose diet is rich in oily fish and meat, have a very low incidence of heart disease
• Other?epidemiological studies?can establish correlations between diet and incidence of disease
• Whilst?it is rare to find a direct causal link?between fat intake and heart disease, the many claims about fats?suggest strongly?that trans-fats have an overall?detrimental effect?on health when consumed in high quantities
• Other conditions linked to trans-fats include
  • Allergy
  • Breast cancer
  • Colonic cancer
  • Cardiovascular diseases
  • Premature birth
  • Preeclampsia (a condition associated with pregnancy)
  • Disorders of the nervous system
  • Vision defects in infants
  • Diabetes
  • Obesity