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2) Food Chemistry I > Lipids V > Flashcards

Lipids V Flashcards

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1
Q

What is hydrogenation?

A

Process used to change the physical and chemical properties of fats and oils by reducing their overall degree of unsaturation.

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2
Q

What are the two functions of hydrogenation?

A
  • Used to convert an oil into a fat

- Reduce the susceptibility of an oil to oxidative rancidity

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3
Q

How is hydrogenation achieved? What is the process?

A
  • Addition of hydrogen (H2) across the double bond of an unsaturated fatty acid of a glyceride
  • Achieved by treating oil with H2 at high temperatures/pressures in the presence of a catalyst (commonly nickel)
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4
Q

What are the two catalysis equations in hydrogenation?

A
  • Oil + Catalyst -> Oil-Catalyst Complex

- Oil-Catalyst Complex + H2 -> Hydrogenated Oil + Catalyst

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5
Q

How do you determine how many double bonds are lost during hydrogenation (catalyst activity)?

A

Defined as decrease in iodine number per unit of time during a hydrogenation under a specific set of conditions

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6
Q

If you consume a little/a lot of iodine, you have a lot of double bonds.

A

A lot of iodine consumed = a lot of double bonds

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7
Q

What is the iodine number?

A

Defined as the number of grams of iodine absorbed by 100 grams of fat.

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8
Q

Why does the iodine number help us determine the number of double bonds? What does it indicate?

A
  • The unsaturated fatty acid residues of the glycerides react with iodine
  • Iodine number indicates the degree of unsaturation of the fatty acid residues on the glycerides
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9
Q

What does a 0.01 mol linoleic acid: 0.02 mole of iodine imply?

A

Every molecule of linoleic acid contains 2 double bonds

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10
Q

Do different fats or oils have different iodine values?

A

Yes, since they have a different triglyceride composition

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11
Q

What are the double bonds capable of?

A

“wandering” (positional isomerism)

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12
Q

What does positional isomerism result in?

A

Conversion of unconjugated double bonds to conjugated double bonds or mixed bonding systems

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13
Q

What does selectivity mean?

A
  • Refers to preferentially hydrogenating more highly UNSATURATED fatty acids
  • Minimum formation of completely saturated fatty acids
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14
Q

How can selectivity be varied?

A

By varying catalysts/operating conditions

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15
Q

What are the factors affecting the reaction rate of hydrogenation?

A

1) Nature of the substance to be hydrogenated
2) Nature and concentration of the catalyst
3) Reaction pressure (concentration of hydrogen)
4) Reaction temperature
5) Degree of agitation

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16
Q

What are the five steps in the hydrogenation of oils?

A

1) Transfer and/or diffusion
2) Adsorption
3) Hydrogenation/Isomerization
4) Desorption
5) Transfer

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17
Q

Which steps are critical for controlling the degree of isomerization and selectivity of reactions in hydrogenation?

A
  • Transfer/Diffusion

- Adsorption

18
Q

What is the transfer step in hydrogenation?

A

Transfer of reactants and products to and from the bulk of the liquid oil phase and outside surface of the catalyst

19
Q

What is the diffusion step in hydrogenation?

A

Diffusion of reactant into the pores of the catalyst; diffusion of products out of the pores of the catalyst

20
Q

What happens if the pores of the catalyst are clogged?

A

The catalyst dies

21
Q

What kind of double bonds are formed during the hydrogenation of linolenic acid?

A

Conjugated double bonds

22
Q

How can selectivity be expressed?

A
  • Ratio Klo/Ko

- The rate of hydrogenation of linoleate relative to that of oleate

23
Q

What determines the selectivity for hydrogenation?

A

Geometric configuration and chemical and physical characteristics of catalyst

24
Q

What happens to linolenic, linoleic, oleic, and stearic during hydrogenation?

A
  • Linolenic: highest at first, drops dramatically
  • Linolenic: drops
  • Oleic: increases
  • Stearic: increases slower than oleic
25
Q

Why does stearic increase slower than oleic during hydrogenation?

A

Because the catalyst favours the two double bonds

26
Q

What are the two types of catalysts for hydrogenation?

A
  • Nickel catalyst

- Copper-Chromium catalyst

27
Q

What does the copper catalyst have a high selectivity for?

A

Linolenic acid (Kln/Klo=10)

28
Q

What is the copper catalyst paired with?

A

Chromium

29
Q

The double-bond migration can form what?

A

Conjugated fatty acids

30
Q

How does the AOCS determine catalyst activity?
Time required to hydrogenate soybean oil to an iodine value of __ from ___ at ___oF, __ psig, ____%
catalyst concentration compared to the time required using AOCS standard catalyst under the same conditions.

A

Time required to hydrogenate soybean oil to an iodine value of 80 from 120 at 350oF, 20 psig, 0.05%
catalyst concentration compared to the time required using AOCS standard catalyst under the same conditions.

31
Q

What is the lifetime of a catalyst?

A

How long a catalyst will remain active and useful

32
Q

Does hydrogenated soybean oil or olive oil contain a lower Iodine Value? Why?

A
  • Olive oil is lower

- Since it contains more monounsaturates

33
Q

What are the independent variables that affect hydrogenation?

A
  • Pressure
  • Temperature
  • Agitation
  • Catalyst concentration
34
Q

What are the dependent variables that affect hydrogenation?

A
  • trans fatty acids
  • Selectivity ratio
  • Hydrogenation rate
35
Q

What are the four analytical methods for modified triglycerides?

A

1) Saponification value
2) Iodine value
3) Gas chromatographic analysis for fatty acids
4) Liquid chromatography

36
Q

If the temperature increases in hydrogenation, how is the selectivity ratio, the trans content, and the reaction rate affected?

A

Selectivity Ratio: increase
Trans content: increase
Reaction Rate: increase

37
Q

If the pressure increases in hydrogenation, how is the selectivity ratio, the trans content, and the reaction rate affected?

A

Selectivity Ratio: Decrease
Trans content: Decrease
Reaction Rate: Increase

38
Q

If the agitation increases in hydrogenation, how is the selectivity ratio, the trans content, and the reaction rate affected?

A

Selectivity Ratio: Decrease
Trans content: Decrease
Reaction Rate: Increase

39
Q

If the catalyst concentration increases in hydrogenation, how is the selectivity ratio, the trans content, and the reaction rate affected?

A

Selectivity Ratio: Increase
Trans content: Increase
Reaction Rate: Increase

40
Q

Which lipid has the property of having a sharp melting point at body temperature?

A

Cocoa fat/butter

2) Food Chemistry I (31 decks)

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