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FDSC251 (Food chem 1) > Lipids lecture 4 + 5 > Flashcards

Lipids lecture 4 + 5 Flashcards

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1
Q

what is knowing the solid fat content important for?

A

to obtain consistent textural characteristics for a fat

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2
Q

2 ways to determine solid fat content?

A
  1. dilatometry

2. nuclear magnetic resonance

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3
Q

what is dilatometry

A

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

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4
Q

how to calculate the solid fat index?

A

SOLIDS (%) AT 25OC = (X(25)/Y) × 100

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5
Q

what is NMR spectroscopy?

A

nuclear magnetic resonance.

based on the alignment of nuclei that have a spin in an applied magnetic field

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6
Q

what is polymorphism?

A

occurrence of several different crystal forms for a single compound).

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7
Q

what are the most common polymorphic forms in order of stability?

A

alpha

beta prima

beta

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8
Q

what is the best TG for chocolate?

A

1-palmito-2-stearo-3-olein and 2-palmito-1-stearo-3-olein

because the temperature for beta prime is closet to body temperature

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9
Q

describe crystal forms of different polymorphic forms

A

refer to slides

crystal:
beta = triclinic = no angles or lengths are equal = no symmetry

beta prime = orthorhombic = same angles but different lengths

hexagonal alpha = same angles and lengths

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10
Q

describe chain length of polymorphic forms

A

alpha: vertical tuning fork. longest distance

beta prime: tilted tuning fork

beta: stacked chair. shortest distance (most compressed)

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11
Q

2 transformation of crystal structures?

A
  1. simple collapse
  2. cataclysmic chain shift

(refer to slides)

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12
Q

2 types of space arrangements of TG crystals?

A
  1. tuning fork form

2. chair form (most likely to be beta)

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13
Q

what are the 4 analytical methods for study of polymorphism?

A
  1. x ray diffraction analyses
  2. microscopic analyses
  3. infrared (IR) spectroscopic analyses
  4. thermal analyses
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14
Q

x ray diffraction analyses of characteristics of TG polymorphs?

A

Alpha:

  • hexagonal
  • tuning fork
  • acyl groups oriented at 90 deg to plan of glyceryl group
  • certical chain orientation
  • longest long spacing
  • randomly ordered
  • most loosely packed
  • platelet
  • 5 um

beta-prime:

  • orthorhombic
  • tuning fork
  • acyl groups are tilted 70deg from plane
  • tilted chain orientation
  • intermediate long spacing
  • in between
  • more closely packed
  • fine needle
  • 1 um

beta

  • triclinic
  • chair form
  • acyl groups tilted about 60deg from plane
  • tilted chain orientation
  • shortest long spacing
  • highly ordered
  • most closely packed
  • long needle
  • 25-50 um
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15
Q

thermal analyses of TG polymorphs?

A

alpha

  • thermodynamically most unstable
  • lowest mp
  • translucent

beta prime

  • thermdynamically unstable
  • intermediate mp

beta

  • most stable
  • highest mp
  • opaque
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16
Q

describe formation of TG polymorphs?

A

alpha
-rapid cooling of liquid fat

beta prime

  • slow cooling of liquid fat
  • polymorphic transformation of alpha form

beta

  • very slow cooling of liquid fat
  • polymorphic transformation of beta-prime
17
Q

steps of conversion from beta to beta-prime of lard

A

interesterification

interesterification and hydrogenation

winterization

addition of cottonseed oil/tallow flakes

[?]

18
Q

why is lard solid even though it has similar composition to veg oils

A
  • high levels of FA in Gs2U and GS3 configuration
  • GS2U = oleoplamitostearin = forms large crystals = grainy texture

-texture can be overcome by interesterification

19
Q

what is interesterification?what is it used for?

A

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

20
Q

what happens if interesterification is carried out at lower temps?

A

more sat long-chain glycerides will fractionally crystallize out

= oil portion becomes more unsaturated = fat portion becomes more saturated

21
Q

what interesterification methods are better for producing highly specific lipids?

A

enzymatic interesterification (using sn-1,3 specific lipase as catalyst)

22
Q

intraesterification vs interesterification?

A

intra: acyl groups exchange positions WITHIN a TG molecule
inter: exchange of acyl groups AMONG TG molecules

23
Q

what are examples of high temp base catalysts?

low temp catalysts?

A

high temp base: KOH and NAOH

low temp: sodium methoxide (NaOCH3)

24
Q

3 steps of the rxn mechanism for interesterification?

A
  1. formation of enolate ion
  2. formation of beta-keto ester
  3. interesterification
25
Q

how is the enulate anion formed in interesterification?

A
  1. alpha proton is removed by base catalyst (ie KOH or NAOH)

2. charge delocalized enulate anion is formed

26
Q

random vs directed interesterification?

A

random:
- carried out at equilibrium conditions
- FA have random distribution among the TG

direct

  • rxn temp is low = when sat TG are produced, they crystallize and are removed from the reaction
  • more saturated glycerides crystallize first
27
Q

what are 3methods of interesterification of lard? what do each of them favor?

A
  1. CML:
    - crystal modified lard
    - favors intramolecule interchange
  2. PML
    - partially modified lard
    - favors random distributions
  3. DIL
    - direct interesterified lard
    - favors directed interesterification
    - can control GS2 content
28
Q

what is enzyme catalyzed interesterification in presence of water used for?

A

manufactor of di and mono GC

emulsifiers

FDSC251 (Food chem 1) (8 decks)

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