fats & oils

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

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AL Chemistry. Fats & Oils. Structure & Properties Hydrolysis of Fats & Oils Iodine Value Hardening of Vegetable Oil Hydrolytic & Oxidative Rancidity. p. 1. AL Chemistry. Structure & Properties (1). Fats and oils = glycerol + fatty acids. Propane-1,2,3-triol. - PowerPoint PPT Presentation

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Page 1: Fats & Oils

Fats & OilsFats & OilsAL Chemistry

p. 1

Structure & Properties Hydrolysis of Fats & Oils Iodine Value Hardening of Vegetable Oil Hydrolytic & Oxidative Rancidity

Page 2: Fats & Oils

Structure & Properties (1)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

Page 3: Fats & Oils

Structure & Properties (2)Structure & Properties (2)

p. 3

AL Chemistry

forms fats(or oils)

with glycerol

Page 4: Fats & Oils

p. 4

Page 5: Fats & Oils

p. 5

Page 6: Fats & Oils

Structure & Properties (3)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

Page 7: Fats & Oils

Hydrolysis of Fats & OilsHydrolysis 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!

Page 8: Fats & Oils

AL Chemistry

p. 8

Iodine Value (1)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.

Page 9: Fats & Oils

p. 9

Fats / Oils Iodine values

Animal fats Butter 25-30

Dripping ( 肉汁 ) 35-65

Lard ( 豬油 ) 45-65

Vegetable oils Coconut oil ( 椰子油 ) 8-10

Soya oil ( 大豆油 ) 80-140

Ground-nut oil ( 花生油 )

85-105

Olive oil ( 橄欖油 ) 80-90

Almond oil ( 杏仁油 ) 90-110

Corn oil ( 粟米油 ) 115-130

Iodine Value (2)Iodine Value (2)# higher iodine value higher degree of unsaturation

Page 10: Fats & Oils

p. 10

Examples of Unsaturated Fatty Acid:Examples of Unsaturated Fatty Acid:

Chemical Names and Descriptions of some Common Fatty Acids

Common Name CarbonAtoms

DoubleBonds

Scientific Name Sources

 Oleic Acid 18 1  9-octadecenoic acid  olive oil

 Linoleic Acid 18 2  9,12-octadecadienoic acid  corn oil

-Linolenic Acid (GLA) 

18 3  6,9,12-octadecatrienoic acid  borage oil

Gadoleic Acid 20 1  9-eicosenoic acid  fish oil

 EPA 20 5  5,8,11,14,17-eicosapentaenoic acid  fish oil

 DHA 22 6  4,7,10,13,16,19-docosahexaenoic acid   fish oil

Page 11: Fats & Oils

p. 11

AL ChemistryHardening of Vegetable OilHardening 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!

Page 12: Fats & Oils

p. 12

Disadvantage of Animal Fats?

They contain larger amount of “Cholesterol”.

AL Chemistry

Page 13: Fats & Oils

p. 13

Hydrolytic and OxidativeRancidity (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.

Page 14: Fats & 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!!

Page 15: Fats & Oils

p. 15

AL Chemistry

C

H

H

C

H

C

H

C

H

H

O2 in the air

AutoxidationC

H

C

H

C

O

C

H

H

H

OH

segment of carboxylic acid in fat/oil hydroperoxide

Oxidative Rancidity (2) :

R-O-O-H[hydroperoxide]

R-O-O[hydroperoxide

free radical]

volatile aldehyde,

ketones ….

“Autoxidation”

Page 16: Fats & Oils

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

Page 17: Fats & Oils

p. 17

AL ChemistryOxidative 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.

Page 18: Fats & Oils

p. 18

AL ChemistryHKALE ….

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)