Fats & Oils AL Chemistry p. 1 Structure & Properties Hydrolysis of Fats & Oils Iodine Value Hardening of Vegetable Oil Hydrolytic & Oxidative Rancidity

Structure & Properties (1) p. 2 Fats and oils = glycerol + fatty acids Propane-1,2,3-triol AL Chemistry if the fatty acid part has many C=C bonds unsaturated

Structure & Properties (2) p. 3 AL Chemistry forms fats (or oils) with glycerol

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Structure & Properties (3) p. 6 AL Chemistry Unsaturated Oils usually have a lower melting point and exist as a liquid. Hydrogenation of some of the C=C bonds converts to solid fats. e.g. Margarine

Hydrolysis of Fats & Oils p. 7 AL Chemistry Fats and oils are hydrolysed into carboxylic acid and glycerol in human body (acidic medium). In lab, hydrolysis can be carried out in alkaline medium more effectively, to give carboxylate and glycerol. (saponification) soap!

AL Chemistry p. 8 Iodine Value (1) ► To measure the degree of unsaturation of a fat or vegetable oil. ► It is defined as the number of grams of iodine that reacts with 100 grams of fats/oils. ► Vegetable has a high iodine value than fats.

p. 9 Fats / OilsIodine values Animal fatsButter25-30 Dripping ( 肉汁 ) Lard ( 豬油 ) Vegetable oils Coconut oil ( 椰子油 ) 8-10 Soya oil ( 大豆油 ) Ground-nut oil ( 花生油 ) Olive oil ( 橄欖油 ) Almond oil ( 杏仁油 ) Corn oil ( 粟米油 ) Iodine Value (2) #higher iodine value  higher degree of unsaturation

p. 10 Examples of Unsaturated Fatty Acid: Chemical Names and Descriptions of some Common Fatty Acids Common Name Carbon Atoms Double Bonds Scientific NameSources Oleic Acid181 9-octadecenoic acid olive oil Linoleic Acid182 9,12-octadecadienoic acid corn oil  -Linolenic Acid (GLA) 183 6,9,12-octadecatrienoic acid borage oil Gadoleic Acid201 9-eicosenoic acid fish oil EPA205 5,8,11,14,17-eicosapentaenoic acid fish oil DHA226 4,7,10,13,16,19-docosahexaenoic acid fish oil

p. 11 AL Chemistry Hardening of Vegetable Oil  Animal fats ---- usually saturated  regular packing higher melting point, therefore solid state at rm temp.  Vegetable oil ---- usually unsaturated  irregular packing (due to presence of cis-isomers) lower melting point, therefore liquid state at rm temp. catalytic (Ni) hydrogenation But the vegetable oil should not be completely hydrogenated, otherwise, the solid will be too hard!

p. 12 Disadvantage of Animal Fats? They contain larger amount of “Cholesterol”. AL Chemistry

p. 13 Hydrolytic and Oxidative Rancidity ( 酸敗 ) of Fats & Oils:  Hydrolytic and Oxidative Reactions of triglyceride molecules give out unpleasant odour……. AL Chemistry due to volatile and foul smelling RCHO & Fatty Acids  Hydrolytic Rancidity occurs due to the presence of moisture in the oils.

p. 14 AL Chemistry  Oxidative Rancidity occurs under exposure to air (oxygen) Oxidative Rancidity (1) :  Very common for those with high iodine value ► high degree of unsaturation --- more susceptible to oxidation!  free radical mechanism!!

p. 15 AL Chemistry Oxidative Rancidity (2) : R-O-O-H [hydroperoxide] R-O-O  [hydroperoxide free radical] volatile aldehyde, ketones …. “Autoxidation”

p. 16 Oxidative Rancidity (3) :  Oxidative Rancidity can be prevented by using antioxidants (BHA or BHT) R-O-O  R-O-O-H i.e. the hydroperoxide free radical is “killed” by the H atom given by BHT  chain reaction stops. AL Chemistry

p. 17 AL Chemistry Oxidative Rancidity (4) :  If the triglyceride molecules do not contain any unsaturation carboxylic acid chain …..  no hydroperoxide will be generated, and therefore oxidative rancidity does not occur.

p. 18 AL Chemistry HKALE ….  1997:Vegetable oil (iodine value, hydrogenation and saponification)  1998:Animal Fats and Vegetable oil (iodine value, hardening, saponification and rancidity)  2001:Vegetable oil [unsaturated oil] (principle of anti-rancidity by BHT)