Lipids IV Flashcards
How is the solid fat content commonly determined?
- Dilatometry
- Nuclear magnetic resonance (NMR) measurements
What is dilatometry based on?
Based on the measurement of the change in specific volume (inverse of density) per unit temperature
How does dilatometry work?
Sample of the fat is simply placed in a reservoir, with a capillary attached
What is measured in dilatometry?
Expansion of the fat is measured as the temperature is changed in specific increments
What is plotted in dilatometry?
The specific volume is plotted as a function of temperature
What kind of curve is plotted in a dilatometry graph? How is it obtained?
- Sigmoidal curve
- Superposition of 3 curves
What do the 3 curves in the specific volume over temperature graph represent?
A) Thermal expansion of the solid fat
B) Expansion due to a change in state
C) Thermal expansion of the liquid only
What ratio can you calculate using the specific volume over temperature graph? Assuming what?
- Ratio of solid to liquid fat at a specific temperature
- Assuming the solid line is parallel to the liquid line
What is the equation for the solid fat index?
Solids (%) at 25oC = (X at 25/Y) x 100
What are the two options for NMR spectroscopy?
- Broad-band NMR
- Pulsed NMR
What is NMR spectroscopy based on?
Alignment of nucleic that have a spin in an applied magnetic field
For the measurement of the solid fat content, what are the NMR signals of interest?
Those from the 1H nuclei in the lipid molecules
How does the pulsed NMR SFC measurement work?
- Sample of fat is placed in a magnetic field
- Radiofrequency (RF) pulse is applied perpendicular to the field to “tip” the spins
What is detected following the application of the 90o RF pulse in NMR?
The free induction decay (FID) is detected
What is the signal accompanying the relaxation process of the 1H magnetic spins after they are disturbed by the RF pulse?
FID (free induction decay)
Which spins of the 1H nucleic relax more rapidly? Compared to what?
Spins in the solid state relax more rapidly than those in the liquid phase
What makes it possible to determine the solid fat content in NMR?
The difference between the spins in the solid state and the liquid state
Which method is simpler and less time-consuming?
NMR is better than dilatometry
What is polymorphism? What exhibits it?
- The occurrence of several different crystal forms for a single compound
- Triglycerides
What are the most common polymorphic forms in order of relative stability?
Alpha (a), beta prime (B’), and beta (B)
Which polymorphic form has the lowest melting form? Which has the highest?
a: lowest
B: highest
What are the four analytical methods for the study of polymorphism?
1) X-ray diffraction analyses
2) Microscopic analyses
3) Infrared (IR) spectroscopic analyses
4) Thermal analyses
How do alpha, beta-prime, and beta polymorphs differ in terms of the cooling of liquid fat?
Alpha: rapid cooling of liquid fat
Beta-Prime: slow cooling of liquid fat
Beta: very slow cooling of liquid fat
Beta-Prime is the polymorphic transformation of what?
Of the alpha form
Beta is the polymorphic transformation of what?
Of beta-prime
What are the four methods for conversion from Beta to Beta-prime?
- Interestification
- Hydrogenation
- Winterization (destearinization)
- Addition of cottonseed oil and/or tallow flakes (beta‐prime)
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?
- Alpha (a)
- Thin, leaf-like crystals
- Random packing arrangement, relatively unstable
What happens when the temperature rises above the temperature of stability for the crystal form?
It will start to change to another crystalline form
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?
- Beta-prime
- Small and uniform, desirable structure
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?
- Beta (B)
- Very dense, large form
- Very undesirable because they are large and grainy
Does the volume increase or decrease as the temperature increase?
Volume increases
What does NMR plot?
Solid fat content as a function of temperature
Which crystal form is the most desirable crystal? At what temperature for it to melt in your mouth?
- Beta-Prime
- 32 to 40 degrees
What is the triclinic beta crystal form?
- None of the angles are equal
- None of the lengths are equal
- The worst crystal you want to have since it has no symmetry
What is the orthorhombic beta-prime crystal form?
- 90o
- Different length
What is the hexagonal alpha crystal form?
- 120o
- Different length
What are the two space arrangements of triglyceride crystals? Which is easier to pack? Which is more likely to form a beta form?
- Tuning fork form
- Chair form
- Chair form is easier to pack
- Chair is more likely to form a beta form
What are alpha crystals made up in terms of forks and chairs?
Vertical tuning fork
What are beta-prime crystals made up in terms of forks and chairs?
Tilted tuning fork
What are beta crystals made up in terms of forks and chairs?
Stacked chair
What are the two ways to transform crystal structures?
- Simple (collapse)
- Cataclysmic (chain shift)
How do the activation energies of the three crystal structures differ? What makes it vary?
- Stability makes it vary
- Alpha is lowest, beta prime is middle, beta is highest
- Alpha is the least stable; beta is the most stable
Which oils prefer the beta crystal form?
- Coconut
- Corn
- Olive
- Lard
- Palm kernal
Which oils prefer the beta-prime crystal form?
- Cottonseed
- Herring
- Tallow
- Milk fat
- Palm
How are the acyl groups oriented (in degrees) from the plane of the glycerol group on each of the triglyceride polymorphs?
Alpha: 90o
Beta-Prime: 68-70o
Beta: 59o
How do the triglyceride polymorphs compare in terms of their long spacing?
Alpha: longest long spacing
Beta-Prime: intermediate
Beta: shortest long spacing
How do the triglyceride polymorphs compare in terms of their packing?
Alpha: more loosely packed
Beta-Prime: more closely packed
Beta: most closely packed
What do the microscopic analyses of the triglyceride polymorphs reveal?
Alpha: platelet (5u)
Beta-Prime: fine needle (1 u)
Beta: long needle (25-50 u)
What does the infrared spectroscopic analyses of the triglyceride polymorphs reveal?
Alpha: singlet at 720cm^-1
Beta-Prime: doublet at 719 and 727 cm^-1
Beta: singlet at 717 cm^-1
How do the triglyceride polymorphs differ in terms of stability and melting point?
Alpha: most unstable, lowest melting point
Beta-Prime: unstable, intermediate melting point
Beta: most stable, highest melting point
What does the color analyses of the triglyceride polymorphs reveal?
Alpha: translucent
Beta-Prime: in-between
Beta: opaque
Why is the specific volume of alpha high?
Since it does not pack well
In lard, the GS2U component is largely made up of ________________, which has a propensity to form ____________.
oleopalmitostearin
large crystals
What is interesterification?
Exchange of fatty acids on the glycerol backbone, using heat and a catalyst such as tin, lead, zinc or alkali earth metals
What happens if interesterification is carried to completion?
- Complete randomization of the fatty acid on the glyceride ‐ Can completely CHANGE the PHYSICAL PROPERTIES of the fat/oil.
What happens if interesterification is carried out at lower temperatures?
- The more saturated long-chain glycerides will fractionally crystallize out
- The oil portion becomes more unsaturated, while the fat portion becomes more saturated
What is the benefit of interesterification?
allows one to change physical properties without forming trans fatty acids (trans‐free margarines).
How is interesterification used for lard?
Used extensively to remove the graininess from lard
Which method is better suited when the aim is to produce lipids with highly specific compositions for functional and medical applications?
Enzymatic interesterification
How can the structure of human milk be reproduced artificially?
Enzymatic interesterification reaction using sn‐1,3 specific lipase as a catalyst
Differentiate interesterification and intraesterification.
Interesterification: exchange of acyl groups among TG molecules
Intraesterification: acyl groups may exchange positions within a TG molecule
Following interesterification, how could you remove SSS?
By lowering the temperature
What are high temperature base catalysts used in interesterification?
KOH and NaOH
What are low-temperature catalysts used in interesterification?
Sodium methoxide (NaOCH3)
What are the 3 steps to interesterification?
1) Formation of enolate ion
2) Formation of B-keto ester
3) Interesterification
What does the base catalyst do in interesterification?
Initial removal of an a‐proton by the base catalyst leads to the charge‐delocalized enulate anion.
What is random esterification?
Interesterification can be carried out to an equilibrium condition, at which point the fatty acids assume an almost random distribution among the triglycerides
What is directed interesterification? What crystallizes first?
- 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.
If you want to get a product with more SSS, what type of interesterification should you use?
Directed
In the interesterification of lard, what do conditions that favor intramolecular interchange result in?
Crystal-modified lard (CML)
In the interesterification of lard, conditions that favor random distribution can be controlled to yield what?
Partially modified lard (PML)
In the interesterification of lard, conditions favoring directed interesterification can be used to control what content? Of what lard?
GS3 content of direct interesterified lard (DIL)
Compare the solid fat index of directed, natural and randomized lard.
- Directed has the highest amount of solid fat (more plasticity)
- Randomized, similar to natural, higher though
- Natural: very low solid fat
What does enzyme-mediated interesterification favour? Why is that important for nutrition?
- 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
How is enzyme-catalyzed interesterification used for the manufacture of emulsifiers?
In the presence of water is also used for the manufacture of di‐ and monoglycerides, extensively used as emulsifiers.
