Lipid: Ahmad Rifai Siwi Shintara Yulihartono
Lipid: Ahmad Rifai Siwi Shintara Yulihartono
Lipid: Ahmad Rifai Siwi Shintara Yulihartono
Definition: Lipids are organic compounds formed mainly from alcohol and fatty acids combined together by ester linkage.
O R CH2 OH
H2O
R
O R CH2 O C R
Fatty alcohol
HO C
ester (lipid)
Lipids are insoluble in water, but soluble in fat or organic solvents (ether, chloroform, benzene, acetone). Lipids include fats, oils, waxes and related compounds. They are widely distributed in nature both in plants and in animals.
Structures of Lipids
Fatty Acids
Long-chain carboxylic acids Insoluble in water Typically 12-18 carbon atoms (even number) Some contain double bonds
11
2-Oleic acid Is the most common fatty acid in natural fats. It is C18:19, i.e., has 18 carbons and one double bond located at carbon number 9 and involving carbon 10.
Source: vegetable oils such as corn oil, linseed oil, peanut oil, olive oil, cottonseed oil, soybean oil and many other plant oils, cod liver oil and animal fats. Deficiency: Their deficiency in the diet leads to nutrition deficiency disease. Its symptoms include: poor growth and health with susceptibility to infections, dermatitis, decreased capacity to reproduce, impaired transport of lipids, fatty liver, and lowered resistance to stress.
1-Linoleic:
It is the most important since other essential fatty acids can be synthesized from it in the body. CH3-(CH2)4-CH = CH-CH2-CH=CH-(CH2)7-COOH
2-Linolenic acid:
in corn, linseed, peanut, olive, cottonseed and soybean oils.
CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH(CH2)7-COOH
3-Arachidonic acid:
It is an important component of phospholipids in animal and in peanut oil from which prostaglandins are synthesized.
CH3-(CH2)4-CH=CH-CH2-CH=CH-CH2-CH=CH-CH2CH=CH-(CH2)3-COOH
20
Sphingolipids
WAXES
Fatty acids + Long chain alcohol Important in fruits: 1. Natural protective layer in fruits, vegetables, etc. 2. Added in some cases for appearance and protection.
O C C H31 15
Triacylglycerols
Glycerol head group HO-CH2CH(OH)-CH2-OH Ester linkage from each hydroxyl to Fatty acid
Fats and oils are Also called triacylglycerols.
Triacylglycerols
In a triacylglycerol, Glycerol forms ester bonds with three fatty acids.
25
Formation of a Triacylglycerol
glycerol + three fatty acids triacylglycerol
O
(CH2)14CH3 CH2 O C
O CH O C O CH2 O C (CH2)14CH3
26
Triacylglycerols in food
Vegetable Oils unsaturated
- catalytic hydrogenation reduces double bonds - less specific than enzymatic methods makes some trans-fats
Properties of Triglycerides
Hydrogenation
Unsaturated compounds react with H2 Ni or Pt catalyst C=C bonds CC bonds
Hydrolysis
Split by water and acid or enzyme catalyst Produce glycerol and 3 fatty acids
Halogenation
29
Hydrogenation
O CH2 O CH CH2 O O C (CH2)5CH CH(CH2)7CH3 O C (CH2)5CH CH(CH2)7CH3 O C (CH2)5CH CH(CH2)7CH3 + 3 H2 Ni
30
Product of Hydrogenation
O CH 2 CH CH 2 O O O C O C (CH 2)14CH 3 O C (CH 2)14CH 3 (CH 2)14CH 3
Hydrogenation converts double bonds in oils to single bonds. The solid products are used to make margarine and other hydrogenated items.
Hydrolysis:
They are hydrolyzed into their constituents (fatty acids and glycerol) by the action of super heated steam, acid, alkali or enzyme (e.g., lipase of pancreas). - During their enzymatic and acid hydrolysis glycerol and free fatty acids are produced.
O CH2 O C R1 O CH2 O C R3 H2C OH O R1 C OH O O C OH
O R2
C O C H
Lipase or Acid
3 H 2O
HO C H H2C OH
+ R C OH 2
R3
Triacylglycerol
Saponification
Alkaline hydrolysis produces glycerol and salts of fatty acids (soaps). Soaps cause emulsification of oily material this help easy washing of the fatty materials
O O CH2 O C R1 O CH2 O C R3 H2C OH HO C H O R1 C ONa O O C ONa
R2 C O C H
+ R C ONa 2
R3
3 NaOH
H2C OH
Triacylglycerol
Halogenation
Neutral fats containing unsaturated fatty acids have the ability of adding halogens (e.g., hydrogen or hydrogenation and iodine or iodination) at the double bonds. - It is a very important property to determine the degree of unsaturation of the fat or oil that determines its biological value
CH3 (CH2)4 CH CH CH2 CH CH (CH2)7 COOH
Linoleic acid 2 I2
CH3 (CH2)4 CH I CH I CH2 CH I CH I (CH2)7 COOH
Stearate-tetra-iodinate
Glycerophospholipids
Glycerophospholipids are The most abundant lipids in cell membranes. Composed of glycerol, two fatty acids, phosphate and an amino alcohol.
Fatty acid Glycerol Fatty acid PO4 Amino alcohol
35
Each glycerophospholipid includes a polar region: glycerol, carbonyl O of fatty acids, Pi, & the polar head group (X)
O R1 C O
H2C CH H2C
C O
R2
P O
glycerophospholipid
polar "kink" due to double bond
non-polar
Sphingosine
Sphingosine is a long-chain unsaturated amino alcohol.
CH3(CH2)12 CH=CHCHOH CHNH2 CH2OH sphingosine
38
Sphingolipids
In sphingomyelin, a sphingolipid found in nerve cells There is an amide bond between a fatty acid and sphingosine, an 18-carbon alcohol.
39
Steroids
Cholesterol Bile Salts Steroid Hormones
PDB 1N83
cholesterol
Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail. Cholesterol is largely hydrophobic. But it has one polar group, a hydroxyl, making it amphipathic.
HO
Cholesterol
PDB 1N83
cholesterol
HO
Cholesterol
Cholesterol in membrane
Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids.
The OH group of cholesterol forms hydrogen bonds with polar phospholipid head groups.
Interaction with the relatively rigid cholesterol decreases the mobility of hydrocarbon tails of phospholipids. But the presence of cholesterol in a phospholipid membrane interferes with close packing of fatty acid tails in the crystalline state, and thus inhibits transition to the crystal state. Phospholipid membranes with a high concentration of cholesterol have a fluidity intermediate between the liquid crystal and crystal states.
Cholesterol in membrane
Cholesterol is abundant in membranes, such as plasma membranes, that include many lipids with long-chain saturated fatty acids.
In the absence of cholesterol, such membranes would crystallize at physiological temperatures. The inner mitochondrial membrane lacks cholesterol, but includes many phospholipids whose fatty acids have one or more double bonds, which lower the melting point to below physiological temperature.
Cholesterol in Foods
Cholesterol is Synthesized in the liver. Obtained from foods. Considered elevated if plasma cholesterol exceeds 200 mg/dL.
TABLE 17.4
46
Bile Salts
cholic acid, a bile acid CH3 OH CH3 CH3 O C N H glycine, an amino acid CH2
COO- Na+
Polar region
HO
Nonpolar region
OH
The function
Emulsification of lipids during digestion. Help in digestion of the other foodstuffs. Activation of pancreatic lipase. Help digestion and absorption of fat-soluble vitamins. Solubilizing cholesterol in bile and prevent gall stone formation. Choleretic action (stimulate their own secretion). Intestinal antiseptic that prevent putrefaction
Steroid Hormones
Steroid hormones Are chemical messengers in cells. Are produced from cholesterol. Include sex hormones such as androgens (testosterone) in males and estrogens (estradiol) in females
low solubility in water transported by proteins, can pass through membranes
H3 C
CH3
8 9
CH3
5 7 6 4
CH3
3
CH2 OH
2 1
CH3
CH 3 H 3C H 3C CH 3 CH 3
Vitamin D2:
H H CH 2
HO
Vitamin E:
R1 R2 HO R3 CH3 CH3 O (CH2 CH2 CH2 CH2 )2 CH2 CH2CH2 CH(CH 3 )2
3.
4. 5. 6.
Iodine Value
Gas Chromatographic Analysis for Fatty Acids Liquid Chromatography Cholesterol Determination
1. Acid Value
Number of mgs of KOH required to neutralize the Free Fatty Acids in 1 g of fat.
AV =
= mg of KOH
2. Saponification Value
Saponification - hydrolysis of ester under alkaline condition.
H2 C HC H2 C
O O C O O C O O C
R R R + 3 KOH
H2 C HC H2 C
O H OH O H + O 3R C OK
1.
2. 3. 4. 5.
5 g in 250 ml Erlenmeyer.
50 ml KOH in Erlenmeyer. Boil for saponification. Titrate with HCl using phenolphthalein. Conduct blank determination.
SP# = 56.1(B -S) x N of HCl Gram of Sample
3. Iodine Number
Molecular weight and iodine number can calculate the number of double bonds. 1 g of fat adsorbed 1.5 g of iodine value = 150.
CH
CH
CH Cl
CH I
2 Na2 S2 O3
Na2 S4 O6
Oleic Acid
Linoleic Acid Linolenic Acid Arachidonic Acid
1
2 3 4
86
173 261 320
Extract fat.
Saponify (hydrolysis under basic condition). Prepare methyl ester (CH3ONa).
4.
5.
6.
14
16
18:2 18
18:3 20 22
21:1
24
Time
5.
Solvent CH3CN/HF
Column 84346 (Waters Associates)
RESPONSE
RETENTION TIME
OL2
O2L OPL O3 OSL
54:5
54:4 52:3 54:3 54:3
44
46 46 48 48
O2P
O2S OPS
52:2
54:2 52:1
48
50 50
OS2
54:1
52
6. CHOLESTEROL DETERMINATION
Enzymatic Determination: Cholesterol Oxidase
CH3O
OCH3 NH2
CH3O
OCH3 NH
H 2 O2 + H2N
Peroxidase
HN
+ H2 O
0-Dianisidine (Colorless)
g/ml Cholesterol
Cholesterol by GLC 1. 2. Prepare cholesterol butyrate. Analyze by GLC. time in GC - 15 min. sensitivity - 10-7 g.
Abs orption at 4 40 nm
g/ml Cholester ol
Cholesterol by GLC
1. 2. Prepare cholesterol butyrate. Analyze by GLC. time in GC - 15 min. sensitivity - 10-7 g.
2.
1. Gravimetric Method
(1) Wet Extraction - Roese Gottlieb & Mojonnier.
For Milk: 1) 10 g milk + 1.25 ml NH4OH mix. solubilizes protein and neutralizes. 2) + 10 ml EtOH - shake. Begins extraction, prevents gelation of proteins. 3) + 25 ml Et2O - shake and mix. 4) + 25 ml petroleum ether, mix and shake.
Sample in thimble is continuously extracted with ether using Soxhlet condenser. After extraction, direct measurement of fat - evaporate ether and weigh the flask.
Soxhlet Method.
REACTIONS OF FATS
Hydrolytic Rancidity:
1. Triglyceride -> Fatty acids Specially C4 butyric acid (or other short chain fatty acids) are the real problem.
2. By lipase.
LIPID OXIDATION
Major flavor problems in food during storage are mainly due to the oxidation of lipid.
1.
2.
Initiation.
Propagation.
3.
Termination.
CH3
(CH )3 2
CH2
13
CH
12
CH
11
CH 2
10
CH
CH
CH 2
COOH
Initiation (metal)
- H.
CH3
(CH )3 2
CH2
.CH
12
12
11
10
CH + O2
11
CH
CH
CH
CH n COOH 2
10
CH
CH + H.
11
CH
CH
CH n COOH 2
10
CH 3
(CH )3 2
CH2
CH O O H
CH _
CH
CH
CH -
CHn COOH 2
Hydroperoxide Decomposition
.OH
11 10 9
12
CH 3
(CH )3 2
CH2
CH
CH
CH
CH
CH
CHn COOH 2
.
CH 3 (CH )3 2
. CH
2
O + H C
12
11
10
CH + H
CH
CH
CH
CH COOH 2n
Termination CH3
(CH )3 2 Pentane
CH3
1.
Peroxide Value
O A. KI + CH 3 C OH HI + CH 3 O C OK
B.
ROOH + 2 HI
I2 +
H2 O +
ROH
C.
I2 + 2 Na2 S 2 O3
2 NaI +
Na2 S4 O6
Peroxide Value =
2. Active Oxygen Method (AOM) Determined the time required to obtain certain peroxide value under specific experimental conditions.
The larger the AOM value, the better the flavor stability of the oil.
3. TBA Test.
To determine the rancidity degree of meat or fish product.
HS N OH N OH + H O C CH2 C H O
HS N
OH
HO CH CH
N N
SH + 2 H2 O
CH OH
OH Colored P igment