Flashcards in Lipids lecture 4 + 5 Deck (28)
what is knowing the solid fat content important for?
to obtain consistent textural characteristics for a fat
2 ways to determine solid fat content?
2. nuclear magnetic resonance
what is dilatometry
technique based on the measurement of the change in specific
volume (the inverse of density) per unit temperature.
expansion of fat is measured as the temp is changed
how to calculate the solid fat index?
SOLIDS (%) AT 25OC = (X(25)/Y) × 100
what is NMR spectroscopy?
nuclear magnetic resonance.
based on the alignment of nuclei that have a spin in an applied magnetic field
what is polymorphism?
occurrence of several different crystal forms for a single compound).
what are the most common polymorphic forms in order of stability?
what is the best TG for chocolate?
1-palmito-2-stearo-3-olein and 2-palmito-1-stearo-3-olein
because the temperature for beta prime is closet to body temperature
describe crystal forms of different polymorphic forms
refer to slides
beta = triclinic = no angles or lengths are equal = no symmetry
beta prime = orthorhombic = same angles but different lengths
hexagonal alpha = same angles and lengths
describe chain length of polymorphic forms
alpha: vertical tuning fork. longest distance
beta prime: tilted tuning fork
beta: stacked chair. shortest distance (most compressed)
2 transformation of crystal structures?
1. simple collapse
2. cataclysmic chain shift
(refer to slides)
2 types of space arrangements of TG crystals?
1. tuning fork form
2. chair form (most likely to be beta)
what are the 4 analytical methods for study of polymorphism?
1. x ray diffraction analyses
2. microscopic analyses
3. infrared (IR) spectroscopic analyses
4. thermal analyses
x ray diffraction analyses of characteristics of TG polymorphs?
-acyl groups oriented at 90 deg to plan of glyceryl group
-certical chain orientation
-longest long spacing
-most loosely packed
-acyl groups are tilted 70deg from plane
-tilted chain orientation
-intermediate long spacing
-more closely packed
-acyl groups tilted about 60deg from plane
-tilted chain orientation
-shortest long spacing
-most closely packed
thermal analyses of TG polymorphs?
-thermodynamically most unstable
describe formation of TG polymorphs?
-rapid cooling of liquid fat
-slow cooling of liquid fat
-polymorphic transformation of alpha form
-very slow cooling of liquid fat
-polymorphic transformation of beta-prime
steps of conversion from beta to beta-prime of lard
interesterification and hydrogenation
addition of cottonseed oil/tallow flakes
why is lard solid even though it has similar composition to veg oils
-high levels of FA in Gs2U and GS3 configuration
-GS2U = oleoplamitostearin = forms large crystals = grainy texture
-texture can be overcome by interesterification
what is interesterification?what is it used for?
exchange of FA on the glycerol backbone using heat and a catalyst (ie tin, lead,zine, alkali earth metals)
causes complete *randomization* of the fatty acid on the glyceride = changes physical properties of the fat/oil WITHOUT forming TRANS FA
use: to remove graininess from lard and to change characteristics of other fats/oils to give other properties
what happens if interesterification is carried out at lower temps?
more sat long-chain glycerides will *fractionally* crystallize out
= oil portion becomes more unsaturated = fat portion becomes more saturated
what interesterification methods are better for producing highly specific lipids?
enzymatic interesterification (using sn-1,3 specific lipase as catalyst)
intraesterification vs interesterification?
intra: acyl groups exchange positions WITHIN a TG molecule
inter: exchange of acyl groups AMONG TG molecules
what are examples of high temp base catalysts?
low temp catalysts?
high temp base: KOH and NAOH
low temp: sodium methoxide (NaOCH3)
3 steps of the rxn mechanism for interesterification?
1. formation of enolate ion
2. formation of beta-keto ester
how is the enulate anion formed in interesterification?
1. alpha proton is removed by base catalyst (ie KOH or NAOH)
2. charge delocalized enulate anion is formed
random vs directed interesterification?
-carried out at equilibrium conditions
-FA have random distribution among the TG
-rxn temp is low = when sat TG are produced, they crystallize and are removed from the reaction
-more saturated glycerides crystallize first
what are 3methods of interesterification of lard? what do each of them favor?
-crystal modified lard
-favors intramolecule interchange
-partially modified lard
-favors random distributions
-direct interesterified lard
- favors directed interesterification
-can control GS2 content