the miscibility of oil and water

Published:

Introduction:

Colloids, of which lipids are usually found in foods in the form, produce stable homogenous state in a condition of a physical mix of different phases of matter. Colloids are important because of the existence in foods, the basis of digestion in human body and the application to the food processing. However, the one of the major concerns about colloids in food and nutrition is how to develop stable mixtures of immiscible lipids and aqueous substances. Considering the aforementioned concern, in the practical, the miscibility of oil and water was examined by making an emulsion which is a stable mix of water and oil and effect of an emulsifying agent, for example, egg yolk on emulsion was also examined. Moreover, a function of lipid involving heat transfer was examined.

Objectives:

The purpose of the practical is to

  1. Determine the miscibility of oil and water by making emulsions in different proportions of oil and water
  2. Examine the effect of a natural emulsifying agent as compared to the condition of part A
  3. Examine the weight, volume and texture change of prawn crackers through deep fat frying
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Method:

All of the experiments were followed by the procedures listed on page 13 and 14 of Laboratory Manuals & Guide 2014.

Result:

The observations are shown in the following:

  1. Determination of the miscibility of oil and water by making emulsions in different proportions of oil and water

The tubes (numbered 1 to 7) which were filled with the mixture of different proportions of vegetable oil and tap water and the length of time they took in seconds for the majority (80% volume) of the two phases to clearly separate were shown in the following table.

Tube No.

1

2

3

4

5

6

7

Volume of vegetable oil (ml)

8

7

6

5

4

3

2

Volume of tap water (ml)

2

3

4

5

6

7

8

80% volume of major phase*(ml)

6.4

5.6

4.8

4

3.2

2.4

1.6

Time to revert to 80% separation (seconds)

1318

478

224

83

70

34

32

*( The vegetable oil was taken to measure the volume of a major phase)

  1. The effect of a natural emulsifying agent as compared to the condition of part A

The tubes (numbered 1 to 7) which were filled with the mixture of different proportions of vegetable oil and tap water were added 10 drops of egg yolk solution and the length of time they took in seconds for the majority (80% volume) of the two phases to clearly separate were shown in the following table.

Tube# No.

1

2

3

4

5

6

7

Volume of vegetable oil (ml)

8

7

6

5

4

3

2

Volume of tap water (ml)

2

3

4

5

6

7

8

80% volume of major phase*(ml)

6.4

5.6

4.8

4

3.2

2.4

1.6

Time to revert to 80% separation (seconds)

3600

3000

2089

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1348

835

248

80

#(The tube was added 10 drops of egg yolk solution)

*( The vegetable oil was taken to measure the volume of a major phase)

  1. The weight, volume and texture change of prawn crackers through deep fat frying

The weight, volume and texture of prawn cracker before and after deep fat frying at 180℃ for 21 seconds for complete expansion of cracker and the change of its physical properties after the complete expansion of cracker were shown in the following table.

Before deep fat frying at 180℃ for 21 seconds

After deep fat frying at 180℃ for 21 seconds

The weight of 25 pieces prawn cracker (g)

32.5

37.76

The weight of a single prawn cracker (g)

1.3

1.5104

The weight change of a single prawn cracker after complete expansion#

(1.5104-1.3) ÷ 1.3 x 100% = 16.18%

∴The weight was increased by 16.18%

The diameter of a single prawn cracker* (cm)

3.3

4.2

The thickness of a single prawn cracker (cm)

0.3

0.6

The volume of a single prawn cracker *(cm3)#

[=πx (diameter÷2)2 x thickness]

πx (3.3 ÷ 2)2 x 0.3 = 2.57

πx (4.2 ÷ 2)2 x 0.6 = 8.31

The volume change of a single prawn cracker (cm3)#

(8.31-2.57) ÷ 2.57 x 100% = 223.97%

∴The volume was increased by 223.97%

The texture of prawn cracker

Firm, hard and had smooth surface

Crispy and had rough and foamed surface

# ( The answer was correct to 2 decimal places.)

*( It was assumed that the shape of a single prawn cracker surface was a circle.)

Discussion:

  1. Determination of the miscibility of oil and water by making emulsions in different proportions of oil and water

According to the result, the greater proportion of oil contained in tube, the longer time was taken for reversion to the majority (80% volume) of the two phases to clearly separate. It meant the longer time duration for the stable mix of oil and water in homogenous state in all proportion of the mixture in tube that had higher proportion of oil and lower proportion of water.

  1. The effect of a natural emulsifying agent as compared to the condition of part A

According to the result, the time for reversion to the majority (80% volume) of the two phases to clearly separate in each tube was consistently longer than that in part A when there was an addition of 10 drops of egg yolk solution in tubes that had the same mixture in part A. It meant the prolonged emulsion which was stable mix of oil and water in homogenous state in all proportion of the mixture in each tube.

The reason was that egg yolk solution acted as a natural emulsifying agent in the process. The active component of emulsifying agent from egg yolk, lecithin facilitated the dispersion of oil as tiny droplets into another.[1][2] Lecithin covered the surface of the oil droplets and prevented the droplets from coalescing and forming continuous phase.[1] Thus, lecithin acted as a surfactant to lower the interfacial tension at the moment to stabilize the emulsion which was stable mix of oil and water in homogenous state in all proportion of the mixture for longer time. [3]

However, non-polar oil molecules and polar water molecules repelled each other later. Since then, the molecules would assembly with other homogenous molecules to decrease the repulsion between molecules. Eventually, there was a separation of two phases.

  1. The weight and volume change of prawn crackers through deep fat frying
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In the practical, the deep fat frying was useful because it fried the prawn crackers very fast and the prawn crackers were not made excessively greasy.[4]

The reason of frying the prawn crackers in very short time is the usage of hot fat, for example, oil for cooking. The nature of oil is lipid that can permit the rapid and efficient transfer of heat and can achieve high temperature. Therefore, deep frying can cook the prawn crackers very fast.

Moreover, the reason of not making the prawn crackers excessively oily is that the moisture in food repels the oil. The hot oil heats the water within the food and steams the food. The oil cannot go opposite direction of the strong flow because the water vapour pushes the bubbles toward the surface.[6]Finally, oil penetration will become narrow to the outer surface.

On the other hand, there is a volume increase in the crackers. The reason is that, during deep fat frying, the prawn crackers are heated and the water in the crackers vaporized into vapour.

The vapour formation leads to the expansion of the structure of starch, which is the main ingredient of the crackers.

Furthermore, there is an increase in weight in the crackers because of the addition of air into the space of foamed prawn crackers during deep fat frying.

Reference:

  1. Emulsions and Emulsifiers, Cookingscienceguy.com http://www.cookingscienceguy.com/pages/wp-content/uploads/2012/07/Emulsions-and-Emulsifiers1.pdf
  2. Emulsion, Wikipedia 2014 http://en.wikipedia.org/wiki/Emulsion
  3. Surfactant, Wikipedia 2014 http://en.wikipedia.org/wiki/Surfactant
  4. Prawn cracker, Wikipedia 2014 http://en.wikipedia.org/wiki/Prawn_cracker
  5. Deep frying, Wikipedia 2014 http://en.wikipedia.org/wiki/Deep_frying#cite_note-1