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FDSC 300 > Lecture 7 - Fat Analysis > Flashcards

Lecture 7 - Fat Analysis Flashcards

1
Q

define a lipid

A

soluble in organic solvents; insoluble or sparingly soluble in water

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2
Q

define total fat according to the FDA

A

sum of fatty acids from C4 to C24 calculated as triglycerides

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3
Q

difference between oils and fats?

A 
oils = liquid at room temp
fats = solids at room temp
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4
Q

what are the 3 classes of lipids?

A

simple lipids, compounds lipids, derived lipids

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5
Q

list examples of simple lipids

A
  • fats
  • waxes
    they are esters of fatty acids with alcohols
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6
Q

list examples of compound lipids

A
  • phospholipids
  • cerebrosides
  • sphingolipids
    they are compounds containing groups in addition to an ester of a fatty acid with an alcohol
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7
Q

list examples of derived lipids

A
  • fatty acids
  • long chain alcohols
  • sterols
  • fat-soluble vitamins
  • hydrocarbons
    substances derived from neutral lipids or compound lipids
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8
Q

why is it important to measure fat content in food materials?

A
  • nutritional evaluation
  • health/diet restrictions
  • food quality (mouthfeel/texture)
  • economic consideration
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9
Q

what unique property of lipids can be exploited for their analysis?

A

level of insolubility in water

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10
Q

what lipids are found in foods?

A
  • triglycerides
  • free fatty acids
  • phospholipids
  • monoglycerides
  • diglycerides
  • sterols
  • complex lipids
  • waxes
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11
Q

what is crude fat?

A

nonpolar lipids only (TG)

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12
Q

how do you find crude fat?

A

dry extraction techniques

Soxhlet and Goldfish methods

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13
Q

what is total lipids?

A

nonpolar AND polar lipids (eg: TG and phospholipids in milk)

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14
Q

how do you find total lipids?

A

wet extraction techniques

Babcock, Gerber, Mojonnier, Bligh & Dyer

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15
Q

what are the dry extraction techniques?

A

Soxhlet, Goldfish

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16
Q

what are the wet extraction techniques?

A

Babcock, Mojonnier, Bligh & Dyer

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17
Q

what techniques utilize solvent extraction?

A

Soxhlet, Goldfish, Mojonnier, Bligh & Dyer

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18
Q

what techniques are non-solvent extracting?

A

Babcock, Gerber

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19
Q

which method is intermittent?

A

Soxhlet

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20
Q

which method is continuous?

A

Goldfish

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21
Q

which methods are discontinuous?

A

Mojonnier, Bligh & Dyer

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22
Q

the extraction of food material by a nonpolar solvent will give an estimate of _____ fat

A

crude

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23
Q

crude fat measures mainly the _____ which in many foods represent more than 95% of total lipids

A

triglycerides

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24
Q

describe the general procedure of a dry extraction technique

A

1) stick dry food sample in nonpolar organic solvent
2) fat makes its merry way into the solvent
3) evaporate the solvent, leaving behind the CRUDE fat

25
Q

ideal solvent properties. go!

A
  • high solvent power for lipids, low for proteins, AAs, and CHO
  • evaporate readily
  • should have relatively low boiling point
  • should not leave behind any residue
  • nonflammable
  • nontoxic
  • penetrate sample particles readily
  • nonhyrgroscopic
  • cost effective
26
Q

the boiling point of an extracting solvent should be (high/low)

A

low

27
Q

list examples of nonpolar organic solvents used for extraction

A
  • hydrocarbons (hexane, heptane, pentane, petroleum ether)
  • diethyl ether (can explode)
  • n-Butanol
28
Q

what is petroleum ether?

A
  • mixture of hexanes and pentanes
  • low boiling point (35-38C)
  • more hydrophobic than diethyl ether
29
Q

discontinuous extraction has a (high/low) ratio of organic solvent to sample

A

high

30
Q

what’s intermittent extraction?

A

solvent is in contact with sample intermittently

31
Q

what is continuous extraction?

A

solvent is always in contact with the sample for a period of time

32
Q

what are the general steps for sample prep?

A

1) remove water
2) reduce particle size (grind)
3) separation of lipid from bound proteins and/or CHO by alkaline or acid hydrolysis

33
Q

what does acid hydrolysis accomplish?

A
  • penetration of solvent into sample

- breaking of covalently and ionically bound lipids to easily extractable forms

34
Q

discontinuous extraction extracts fats from a sample with a _____ volume of solvent

A

fixed

35
Q

limitations of discontinuous extraction?

A
  • needs large amount of solvent

- low efficiency (as solvent extracts fat, its ability to keep extracting decreases)

36
Q

describe a Soxhlet instrument

A
  • flask holds solvent
  • siphoning unit
  • paper thimble holds food
  • condenser
37
Q

what are the steps of soxhlet extraction?

A

1) sample placed in paper thimble
2) solvent builds up in extraction chamber
3) solvent accumulates in extraction chamber for 5-10 mins
4) solvent + crude fat siphons back into boiling flask
5) remove flask and evaporate off solvent
6) measure crude fat weight or volume left

38
Q

what variables should be considered during crude fat determination?

A
  • sample prep
  • choice of solvent
  • extraction (time, temp, particle size)
39
Q

the goldfish method is based on a _____ _____ of solvent evaporating and being condensed

A

closed loop

40
Q

what is the biggest limitation of the Goldfish method?

A

formation of a solvent channel in the sample (fire hazard)

41
Q

what makes a method a “dry” or “wet” method?

A

presence (wet) or absence (dry) of polar solution

42
Q

babcock method is a (dry/wet) extraction

A

wet (nonsolvent)

43
Q

babcock method measures _____ fat

A

total

44
Q

true or false: a sample used for babcock extraction must contain water

A

true

45
Q

which method is primarily used for determining milk fat?

A

Babcock method

46
Q

describe the Babcock method

A
  • H2SO4 is added to wet sample in the presence of heat
  • centrifugation
  • fat blob is measured volumetrically or by the graduated portion of babcock bottle
47
Q

limitation of babcock method?

A

sulfuric acid can char sugar and chocolate. not suitable for chocolate or added sugar products.

48
Q

gerber method is a _____ extraction

A

wet (nonsolvent)

49
Q

describe the gerber method

A
  • H2SO4 AND isoamyl alcohol is added to wet sample in the presence of heat
  • centrifugation
  • fat blob is measured volumetrically
50
Q

what does the addition of isoamyl alcohol do? what method am i talking about?

A

method: gerber
purpose: prevents charring of sugar

51
Q

what kind of food commodities are suitable for the Mojonnier method?

A

milk, dairy products, fish, meat

52
Q

describe the Mojonnier method

A
  • NH4OH dissolves protein of casein micelle membranes and fat globule membranes to separate bound lipids. also neutralizes acidic sample
  • EtOH prevents gel formation
  • diethyl ether and petroleum ether solubilize and extract fat
53
Q

why use petroleum ether for the Mojonnier method?

A

prevents absorption of water by diethyl ether and dissolves more nonpolar lipids

54
Q

what food commodities are suitable for the Bligh and Dyer method?

A

fish and seafoods, meat and meat products

55
Q

what reagents are used in the Bligh and Dyer method?

A

Chloroform, methanol, and water

56
Q

describe the Bligh and Dyer method

A
  • samples homogenized in chloroform-methanol solution, then filtered into collection tube
  • KCl (aq) solution is added to chloroform-methanol mixture containing the extracted fats to make 2 phases (lipid in chloroform phase on bottom)
  • phases separated by separatory funnel or centrifugation
  • evaporation of chloroform
57
Q

what instrumental methods are there for fat determination?

A
  • IR method
  • Specific Gravity (Foss-Let Method)
  • Nuclear Magnetic Resonance
58
Q

what’s the IR method?

A

fat can absorb IR energy at wavelength 3.73 um; the more the energy absorption, the higher the fat content

FDSC 300 (9 decks)

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