Lipid Emulsification and Degree of Unsaturation

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Iodine and tween-80 solutions are eye and skin irritants, PPE and appropriate laboratory attire must be worn at all times. Iodine spills must be diluted with water before drying the solution (MSDS: Iodine Solution, n.d.). After finishing with the second part of the experiment, all iodine-containing solution must be disposed in the halogenated organic waste container (Dangkulwanich, 2017).

Results

Time

Tube no.

1

2

3

Immediately

cloudy

cloudy

cloudy

1 minute

Two layers formed: opaque white and translucent white

Two layers formed: opaque white and translucent white

Two layers formed: opaque white and translucent white

5 minutes

No change

The opaque white layer became larger than the translucent layer.

The opaque white layer became larger than the translucent layer, but smaller than tube 2 in relative size

30 minutes

The opaque white layer became larger than the translucent white layer, but smaller than tube 2 and 3 in relative size

The opaque white layer became even larger than the translucent white layer. Tube 2 has the largest opaque white layer in relative size

The opaque white layer became even larger than the translucent white layer, but smaller than tube 2 in relative size

Table #1 Summarizes the results of the lipid emulsification observed through layer formation after each period of time.

Note: There is a distinct white small layer on top in tube 2

Tube Contents

Time elapsed (minutes)

Coconut oil

1.09

Oleic acid

2.30

Olive oil

3.58

Soybean oil

4.17

Vegetable shortening

5.58

Lard

11.22

Table #2 Summarizes the time elapsed for the color of iodine to disappear for various lipids

Discussion

The results of the first part of the experiment support our hypothesis. The solution in tube 1 contains no emulsifiers, so the rate at which the opaque white layer becomes larger is the slowest among the three tubes as expected. In fact, the time elapsed for 1 minute and 5 minutes for tube 1 shows no change in layer formation. After 30 minutes, tube 2 has the highest rate at which the opaque white layer becomes larger. It was so large than the solution in tube 2 almost confer a complete emulsification; thus, tween-80 solution is a better emulsifier as expected. Further observation shows that the two layers become clearer and we observed small white layer on top in tube 2. This is because tween-80 form emulsions by reducing the surface tension of the substances to be emulsified (Tween 80, n.d.), making the solution more distinguishable.

[pic 1]

Figure 1: The structure of Tween-80 (Dangkulwanich, 2017)

[pic 2]

Figure 2: The structure of soap (Know encyclopedia, n.d.)

The reason why tween-80 is a better emulsifier than soap is because of their structure. Since we cannot find any literature that relates tween-80 structure to its function, we hypothesized that the bulky head of tween-80 makes the overall molecule more cone-like; thus, less tween-80 is required for micelle formation. Plus, the kinked tail of the micelle makes the overall structure of the micelle flexible capable of interacting with more water molecule (Figure 1). Soap, on the other hand, has a less bulky head and no kink, which maximizes tail to tail interaction making it less flexible.

The second part of the experiment supports our hypothesis on lard as the least unsaturated fatty acid and rejects our hypothesis on soybean as the most unsaturated fatty acid. It turns out that coconut oil, olive oil, and oleic acid have a higher level of unsaturation than soybean oil. To know whether our results align with real results, we used degrees of saturation as our unit of reference. We will use figure 3 to determine how unsaturated a molecule is. The higher the unsaturation, the higher chance that the halogens will attack the fatty acid; thus, eliminating the double bond causing the color to disappear faster (Vollhardt & Schore).

[pic 3]

Figure 3: Degree of unsaturation (James, n.d.)

Ranked by decreasing unsaturation, the order of our results is coconut oil, oleic oil, olive oil, soybean oil, vegetable shortening, and lard. The order of the fatty acid ranked according to the degree of unsaturation (table 3) is soybean oil, coconut oil, olive oil, oleic acid, and lard. Even though we have no information on the structure of the vegetable oil, it should have a similar degree of unsaturation with lard. Unsaturated fatty acids can be converted into saturated by the process of hydrogenation (Hudson, 2017). Depending upon the degree of unsaturation, the fatty acids can combine with oxygen or halogens to form saturated fatty acid (James, n.d.) and vegetable shortening is made from vegetable oils by adding hydrogen to the double bonds and become more saturated. Thus, it should have a low degree of unsaturation. Based on the degree of unsaturation, our hypothesis on soybean would be correct. It makes sense because soybean has a melting point of -16 degree