Lipids IV Flashcards by Sophie Lamontagne

How is the solid fat content commonly determined?

Dilatometry

- Nuclear magnetic resonance (NMR) measurements

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What is dilatometry based on?

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

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How does dilatometry work?

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

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What is measured in dilatometry?

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

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What is plotted in dilatometry?

The specific volume is plotted as a function of temperature

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

Sigmoidal curve

- Superposition of 3 curves

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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

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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

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What is the equation for the solid fat index?

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

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What are the two options for NMR spectroscopy?

Broad-band NMR

- Pulsed NMR

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What is NMR spectroscopy based on?

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

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

Those from the 1H nuclei in the lipid molecules

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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

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

The free induction decay (FID) is detected

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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)

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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

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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

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Which method is simpler and less time-consuming?

NMR is better than dilatometry

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What is polymorphism? What exhibits it?

The occurrence of several different crystal forms for a single compound
Triglycerides

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

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

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

a: lowest
B: highest

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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

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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

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Beta-Prime is the polymorphic transformation of what?

Of the alpha form

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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.