F.2.1 Describe the difference in structure between saturated and unsaturated (mono and poly-unsaturated) fatty acids
- saturated fats contain only single carbon-carbon bonds within the tail of the fatty acid chains
- the fats pack closely because of the single bonds so although London forces are weak, the R groups interact enough to form solids at room temperature
- unsaturated fatty acids have at least one double bond (C=C) in at least one chain
- mono-unsatured fats have one double bond per chain
- poly-unsaturated fats have more than one double bond per chain
- the double bonds prevent the fats from packing closely enough, so they’re liquid at room temperature
- most naturally occurring fats contain a mixture of saturated, mono-unsaturated, and poly-unsaturated fatty acids and are classified according to the predominant type of unsaturation present
F.2.2 Predict the degree of crystallization (solidification) and melting point of fats and oils from their structure, and explain the relevance of this property in the home and in industry
- solid fats are more likely to be crystallize, more saturated and/or have longer fatty acid hydrocarbon chains
- mono-unsaturated (olive, canola, and peanut) and poly-unsaturated fats (safflower, sunflower, corn, fish, linoleum and linolenic acid) are liquids
- saturated fats (palm, coconut, lard, butter, and shortening) are solids at room temperature
- the melting point of fatty acids increases with increasing relative molecular mass and increasing degree of saturation
- fats and oils are chosen for cooking based on their melting temperature
- e.g.) cocoa butter melts at close to body temperature, and fats chosen for cake-making melt over a wide range of temperatures
- cis fatty acids (the hydrogen atoms are on the same side of the carbon-carbon double bond) have lower melting points than trans fatty acids (the hydrogen atoms are on opposite sides of the carbon-carbon double bonds)
F.2.3 Deduce the stability of fats and oils from their structure
- saturated fats are more stable than unsaturated fats
- the carbon-carbon double bonds in unsaturated fats react with oxygen (auto-oxidation), hydrogen (hydrogenation), light (photo-oxidation), and enzymes/heat/water (hydrolysis)
F.2.4 Describe the process of hydrogenation of unsaturated fats
- the addition of hydrogen in the presence of heat (140-225°C) and a nickel (or zinc or copper) catalyst increases the amount of saturation in a fat
F.2.5 Discuss the advantages and disadvantages of hydrogenating fats and oils