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2) Food Chemistry I > Lipids IV > Flashcards

Lipids IV Flashcards

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1
Q

How is the solid fat content commonly determined?

A
  • Dilatometry

- Nuclear magnetic resonance (NMR) measurements

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2
Q

What is dilatometry based on?

A

Based on the measurement of the change in specific volume (inverse of density) per unit temperature

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3
Q

How does dilatometry work?

A

Sample of the fat is simply placed in a reservoir, with a capillary attached

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4
Q

What is measured in dilatometry?

A

Expansion of the fat is measured as the temperature is changed in specific increments

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5
Q

What is plotted in dilatometry?

A

The specific volume is plotted as a function of temperature

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6
Q

What kind of curve is plotted in a dilatometry graph? How is it obtained?

A
  • Sigmoidal curve

- Superposition of 3 curves

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7
Q

What do the 3 curves in the specific volume over temperature graph represent?

A

A) Thermal expansion of the solid fat
B) Expansion due to a change in state
C) Thermal expansion of the liquid only

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8
Q

What ratio can you calculate using the specific volume over temperature graph? Assuming what?

A
  • Ratio of solid to liquid fat at a specific temperature

- Assuming the solid line is parallel to the liquid line

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9
Q

What is the equation for the solid fat index?

A

Solids (%) at 25oC = (X at 25/Y) x 100

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10
Q

What are the two options for NMR spectroscopy?

A
  • Broad-band NMR

- Pulsed NMR

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11
Q

What is NMR spectroscopy based on?

A

Alignment of nucleic that have a spin in an applied magnetic field

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12
Q

For the measurement of the solid fat content, what are the NMR signals of interest?

A

Those from the 1H nuclei in the lipid molecules

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13
Q

How does the pulsed NMR SFC measurement work?

A
  • Sample of fat is placed in a magnetic field

- Radiofrequency (RF) pulse is applied perpendicular to the field to “tip” the spins

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14
Q

What is detected following the application of the 90o RF pulse in NMR?

A

The free induction decay (FID) is detected

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15
Q

What is the signal accompanying the relaxation process of the 1H magnetic spins after they are disturbed by the RF pulse?

A

FID (free induction decay)

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16
Q

Which spins of the 1H nucleic relax more rapidly? Compared to what?

A

Spins in the solid state relax more rapidly than those in the liquid phase

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17
Q

What makes it possible to determine the solid fat content in NMR?

A

The difference between the spins in the solid state and the liquid state

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18
Q

Which method is simpler and less time-consuming?

A

NMR is better than dilatometry

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19
Q

What is polymorphism? What exhibits it?

A
  • The occurrence of several different crystal forms for a single compound
  • Triglycerides
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20
Q

What are the most common polymorphic forms in order of relative stability?

A

Alpha (a), beta prime (B’), and beta (B)

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21
Q

Which polymorphic form has the lowest melting form? Which has the highest?

A

a: lowest
B: highest

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22
Q

What are the four analytical methods for the study of polymorphism?

A

1) X-ray diffraction analyses
2) Microscopic analyses
3) Infrared (IR) spectroscopic analyses
4) Thermal analyses

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23
Q

How do alpha, beta-prime, and beta polymorphs differ in terms of the cooling of liquid fat?

A

Alpha: rapid cooling of liquid fat
Beta-Prime: slow cooling of liquid fat
Beta: very slow cooling of liquid fat

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24
Q

Beta-Prime is the polymorphic transformation of what?

A

Of the alpha form

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25
Q

Beta is the polymorphic transformation of what?

A

Of beta-prime

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26
Q

What are the four methods for conversion from Beta to Beta-prime?

A
  • Interestification
  • Hydrogenation
  • Winterization (destearinization)
  • Addition of cottonseed oil and/or tallow flakes (beta‐prime)
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27
Q

If you melt a fat first and then cool it quickly, the majority of the triglycerides will crystallize into what form? What shape are the crystals? Is it stable?

A
  • Alpha (a)
  • Thin, leaf-like crystals
  • Random packing arrangement, relatively unstable
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28
Q

What happens when the temperature rises above the temperature of stability for the crystal form?

A

It will start to change to another crystalline form

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29
Q

If you re-melt and cool a fat more slowly, giving more time for molecular arrangement, which crystalline structure will form? What is the shape? Is it desirable?

A
  • Beta-prime

- Small and uniform, desirable structure

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30
Q

If you re-melt and cool a fat more VERY slowly, giving more time for molecular arrangement, which crystalline structure will form? What is the shape? Is it desirable?

A
  • Beta (B)
  • Very dense, large form
  • Very undesirable because they are large and grainy
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31
Q

Does the volume increase or decrease as the temperature increase?

A

Volume increases

32
Q

What does NMR plot?

A

Solid fat content as a function of temperature

33
Q

Which crystal form is the most desirable crystal? At what temperature for it to melt in your mouth?

A
  • Beta-Prime

- 32 to 40 degrees

34
Q

What is the triclinic beta crystal form?

A
  • None of the angles are equal
  • None of the lengths are equal
  • The worst crystal you want to have since it has no symmetry
35
Q

What is the orthorhombic beta-prime crystal form?

A
  • 90o

- Different length

36
Q

What is the hexagonal alpha crystal form?

A
  • 120o

- Different length

37
Q

What are the two space arrangements of triglyceride crystals? Which is easier to pack? Which is more likely to form a beta form?

A
  • Tuning fork form
  • Chair form
  • Chair form is easier to pack
  • Chair is more likely to form a beta form
38
Q

What are alpha crystals made up in terms of forks and chairs?

A

Vertical tuning fork

39
Q

What are beta-prime crystals made up in terms of forks and chairs?

A

Tilted tuning fork

40
Q

What are beta crystals made up in terms of forks and chairs?

A

Stacked chair

41
Q

What are the two ways to transform crystal structures?

A
  • Simple (collapse)

- Cataclysmic (chain shift)

42
Q

How do the activation energies of the three crystal structures differ? What makes it vary?

A
  • Stability makes it vary
  • Alpha is lowest, beta prime is middle, beta is highest
  • Alpha is the least stable; beta is the most stable
43
Q

Which oils prefer the beta crystal form?

A
  • Coconut
  • Corn
  • Olive
  • Lard
  • Palm kernal
44
Q

Which oils prefer the beta-prime crystal form?

A
  • Cottonseed
  • Herring
  • Tallow
  • Milk fat
  • Palm
45
Q

How are the acyl groups oriented (in degrees) from the plane of the glycerol group on each of the triglyceride polymorphs?

A

Alpha: 90o
Beta-Prime: 68-70o
Beta: 59o

46
Q

How do the triglyceride polymorphs compare in terms of their long spacing?

A

Alpha: longest long spacing
Beta-Prime: intermediate
Beta: shortest long spacing

47
Q

How do the triglyceride polymorphs compare in terms of their packing?

A

Alpha: more loosely packed
Beta-Prime: more closely packed
Beta: most closely packed

48
Q

What do the microscopic analyses of the triglyceride polymorphs reveal?

A

Alpha: platelet (5u)
Beta-Prime: fine needle (1 u)
Beta: long needle (25-50 u)

49
Q

What does the infrared spectroscopic analyses of the triglyceride polymorphs reveal?

A

Alpha: singlet at 720cm^-1
Beta-Prime: doublet at 719 and 727 cm^-1
Beta: singlet at 717 cm^-1

50
Q

How do the triglyceride polymorphs differ in terms of stability and melting point?

A

Alpha: most unstable, lowest melting point
Beta-Prime: unstable, intermediate melting point
Beta: most stable, highest melting point

51
Q

What does the color analyses of the triglyceride polymorphs reveal?

A

Alpha: translucent
Beta-Prime: in-between
Beta: opaque

52
Q

Why is the specific volume of alpha high?

A

Since it does not pack well

53
Q

In lard, the GS2U component is largely made up of ________________, which has a propensity to form ____________.

A

oleopalmitostearin

large crystals

54
Q

What is interesterification?

A

Exchange of fatty acids on the glycerol backbone, using heat and a catalyst such as tin, lead, zinc or alkali earth metals

55
Q

What happens if interesterification is carried to completion?

A
  • Complete randomization of the fatty acid on the glyceride ‐ Can completely CHANGE the PHYSICAL PROPERTIES of the fat/oil.
56
Q

What happens if interesterification is carried out at lower temperatures?

A
  • The more saturated long-chain glycerides will fractionally crystallize out
  • The oil portion becomes more unsaturated, while the fat portion becomes more saturated
57
Q

What is the benefit of interesterification?

A

allows one to change physical properties without forming trans fatty acids (trans‐free margarines).

58
Q

How is interesterification used for lard?

A

Used extensively to remove the graininess from lard

59
Q

Which method is better suited when the aim is to produce lipids with highly specific compositions for functional and medical applications?

A

Enzymatic interesterification

60
Q

How can the structure of human milk be reproduced artificially?

A

Enzymatic interesterification reaction using sn‐1,3 specific lipase as a catalyst

61
Q

Differentiate interesterification and intraesterification.

A

Interesterification: exchange of acyl groups among TG molecules
Intraesterification: acyl groups may exchange positions within a TG molecule

62
Q

Following interesterification, how could you remove SSS?

A

By lowering the temperature

63
Q

What are high temperature base catalysts used in interesterification?

A

KOH and NaOH

64
Q

What are low-temperature catalysts used in interesterification?

A

Sodium methoxide (NaOCH3)

65
Q

What are the 3 steps to interesterification?

A

1) Formation of enolate ion
2) Formation of B-keto ester
3) Interesterification

66
Q

What does the base catalyst do in interesterification?

A

Initial removal of an a‐proton by the base catalyst leads to the charge‐delocalized enulate anion.

67
Q

What is random esterification?

A

Interesterification can be carried out to an equilibrium condition, at which point the fatty acids assume an almost random distribution among the triglycerides

68
Q

What is directed interesterification? What crystallizes first?

A
  • Interesterification can be directed away from its usually random end‐point if the fat is allowed to crystallize during reactions.
  • The trisaturated glycerides crystallize first.
69
Q

If you want to get a product with more SSS, what type of interesterification should you use?

A

Directed

70
Q

In the interesterification of lard, what do conditions that favor intramolecular interchange result in?

A

Crystal-modified lard (CML)

71
Q

In the interesterification of lard, conditions that favor random distribution can be controlled to yield what?

A

Partially modified lard (PML)

72
Q

In the interesterification of lard, conditions favoring directed interesterification can be used to control what content? Of what lard?

A

GS3 content of direct interesterified lard (DIL)

73
Q

Compare the solid fat index of directed, natural and randomized lard.

A
  • Directed has the highest amount of solid fat (more plasticity)
  • Randomized, similar to natural, higher though
  • Natural: very low solid fat
74
Q

What does enzyme-mediated interesterification favour? Why is that important for nutrition?

A
  • Favours leaving the fatty acid in the middle intact

- Nutrition: fatty acid in the 2nd position is the one that we metabolize in our diet

75
Q

How is enzyme-catalyzed interesterification used for the manufacture of emulsifiers?

A

In the presence of water is also used for the manufacture of di‐ and monoglycerides, extensively used as emulsifiers.

2) Food Chemistry I (31 decks)

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