You are working with a company that is interested in identifying food applicatio
ID: 704474 • Letter: Y
Question
You are working with a company that is interested in identifying food applications for coconut oil and linseed oil.You have been asked to compare the physicochemical properties of these 2 oils.The fatty acid profile of the oils is listed in the table below.
Fatty Acid
Coconut Oil (%)
Linseed Oil (%)
C6:0
0.50
C8:0
8.0
C10:0
6.4
C12:0
48.5
C14:0
17.6
Palmitic acid (%)
8.4
4.8
Stearic acid (%)
2.5
4.7
Oleic acid (%)
6.5
19.9.
Linoleic acid (%)
1.6
16.9
Linolenic acid (%)
53.7
a. Predict which oil would have the highest melting point. Discuss why. In your answer, discuss the 2 characteristics of the fatty acids that affect the melting point.
b. Which of the oils would be most likely to undergo lipid oxidation reactions to produce off-flavors? In your answer, compare the relative susceptibility of the individual fatty acids to oxidation.
c. In the table below, identify all products that would form if linseed oil was partially hydrogenated and fully hydrogenated.
Partially Hydrogenated Linseed Oil
Fully Hydrogenated Linseed Oil
d. Discuss the effects of hydrogenation on the melting point of the linseed oil.
e. Linseed oil and coconut oil are interesterified in a 1:1 ratio. In the table below, indicate the fatty acid profile of the new interesterified fat in the table below.
Fatty Acid
Coconut Oil
Linseed Oil
New Interesterified Fat
C6:0
0.50
C8:0
8.0
C10:0
6.4
C12:0
48.5
C14:0
17.6
Palmitic acid (%)
8.4
4.8
Stearic acid (%)
2.5
4.7
Oleic acid (%)
6.5
19.9.
Linoleic acid (%)
1.6
16.9
Linolenic acid (%)
53.7
f. Compare the susceptibility of the linseed oil and new interesterfied fat to lipid oxidation. Discuss how interesterification alters the susceptibility of the linseed oil to lipid oxidation.
Fatty Acid
Coconut Oil (%)
Linseed Oil (%)
C6:0
0.50
C8:0
8.0
C10:0
6.4
C12:0
48.5
C14:0
17.6
Palmitic acid (%)
8.4
4.8
Stearic acid (%)
2.5
4.7
Oleic acid (%)
6.5
19.9.
Linoleic acid (%)
1.6
16.9
Linolenic acid (%)
53.7
Explanation / Answer
a.
Long chain fatty acids possess more carbon atoms. The carbon atoms are bonded together thereby resulting in more bonds. Melting is as a result of breaking these bonds. The longer the carbon chains the higher the molecular weight of t6he fatty acids hence more energy that comes from a higher temperature.
The geometry of the double bond is almost always a cis configuration in natural fatty acids. These molecules do not "stack" very well. The intermolecular interactions are much weaker than saturated molecules. As a result, the melting points are much lower for unsaturated fatty acids.
Unsaturated fatty acids have lower melting points than saturated fatty acids of the same length. For example, the melting point of stearic acid is 69.6°C, whereas that of oleic acid (which contains one cis double bond) is 13.4°C. The melting points of polyunsaturated fatty acids of the C18 series are even lower.
Oil
Melting Temperature (oC)
Coconut Oil
25
Linseed Oil
-24
b.
Oil oxidation is an undesirable series of chemical reactions involving oxygen that degrades the quality of an oil. Oxidation eventually produces rancidity in oil, with accompanying off flavors and smells. All oil is in a state of oxidation - you cannot stop it completely - but there are ways to reduce it.
Lipid
Experimental protocol
Oxidation induction times (OIT, min)
Linseed
- 130?C
- 5 mg in a sealed pan - Flow rate = 60 mL/min
- Linseed: OIT130?C = 23.1
- Linseed + 0.05% of antioxidant blend = 25.1
- Linseed + 0.2% of antioxidant blend = 33.1
- Linseed + 0.01% Butylated hydroxyl anisole (BHA) = 24 - Linssed + 0.02% BHA = 30.1
Coconut
- 110-140?C.
- 5 mg in an open pan
- Flow rate = 50 mL/min
- Coconut:
OIT110-140?C = 325-44;
Ea = 86.9;
k128?C = 0.011
The melting point of some oils increase with an increase of fatty acid chain length, and decreases with desaturation rate, which increases relative susceptibility to oxidation. In general, vegetable oils are rich with unsaturated long chained triglycerides, with the exception of coconut and palm oils, which are rich in saturated medium chained triglycerides.
c. and d.
Linseed oil was partially hydrogenated, using both continuous and batch processes.
Vegetable oils, with their higher degrees of unsaturation, can be converted to solids via reaction with hydrogen in a process called hydrogenation.
The yellowing of linseed oil upon hydrogenation appears to be a function of both
1) the quantity of fatty acids more unsaturated than oleic present in the oil and
2) the ratio of the quantity of linolenic acid radicals to linoleic acid radicals present.
Oil
Melting Temperature (oC)
Coconut Oil
25
Linseed Oil
-24
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