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5) FDSC 300 > Lecture 7- Lipid Analysis > Flashcards

Lecture 7- Lipid Analysis Flashcards

1
Q

What are lipids?

A

Soluble in organic solvents, insoluble/sparingly soluble in water

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2
Q

What is the FDA definition of lipids?

A

Total fat is the sum of fatty acids C4-C24 calculated as TG

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3
Q

What are oils?

A

TG that are liquid at room temp

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4
Q

What are fats?

A

TG that are solid at room temp

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5
Q

What is the bond that hold the glycerol molecule to the TG?

A

Ester bond

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6
Q

What are the 3 classes of lipids?

A
  1. Simples
  2. Compound
  3. Derived
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7
Q

Simple Lipid

A

Ester of fatty acids with alcohol

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8
Q

Compound lipid

A

Compounds containing groups in addition to an ester of a fatty acid with an alcohol ( phospholipids, cerebosides, sphingolipids)

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9
Q

Derived Lipids

A

substances drived from neutral lipids or lipid compounds ( FA, sterols, hydrocarbons)

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10
Q

Why is it important for measure fat content?

A
  • Nutriton
  • Health/diet restrictions
  • Food quality
  • Economic considerations
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11
Q

What makes it possible to seperate lipids from proteins and carbohydrates?

A

Insolubility

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12
Q

What is the hydrophobicity of lipids depend on?

A

Molecular constituents

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13
Q

What is crude fat?

A

In non polar lipids, TG

–> using non polar organic solvent

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14
Q

What method extracts crude fat?

A

Dry extraction

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15
Q

What are the methods of dry extraction?

A

Soxhelt and goldfish

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16
Q

What is total lipids?

A

Non polar and polar lipids

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17
Q

How are total lipids extracted?

A

wet extraction

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18
Q

What are the methods of wet extraction?

A

Babcock, berger, Majonnier, Bligh&Dyer

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19
Q

What are the two types of fat extraction based on type of chemical?

A

Solvent and non solvent

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20
Q

What are the solvent methods?

A

Soxhelt, Goldfish, Majonnier, Bligh & Dyer

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21
Q

What are the non solvent methods?

A

Babcock, Gerber

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22
Q

What is crude fat refered to in the determination?

A

Residue obtained after removal of the non polar organic solvent used to extract dried sample

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23
Q

The extraction of food material by a non polar solvent will give an estimate of…

A

Crude fat, no total lipds

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24
Q

What is the major lipid components in food?

A

TG

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25
Q

What does Crude fat mainly measure?

A

TG

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26
Q

What is the overview of crude analysis?

A

Dry food samples–> (extraction w/ non polar organic solvent) –> solution of fat in the solvent–>(evaporation of organic solvent –> residue (Crude fat)

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27
Q

The non polar organic solvent only extracts…

A

non polar materials

28
Q

What are the ideal solvent properties?

A

Should have a high solvent power for lipids and low or no solvent power for proteins, amino acids, and carbohydrates
Should evaporate readily and leave no residue
Should have a relatively low boiling point
Should not leave behind any residue
Should be nonflammableand nontoxic
Should penetrate sample particles readily
Should be nonhygroscopic
Should be cost effective

29
Q

What are some examples of polar organic solvents used?

A

Hydrocarbon ( petroleum ether, low boiling point, volatile, non polar)
Diethyl (more polar, absorbs O2 and forms peroxides which in presence of heat could explode)
n-Butanol ( more polar than other solvents)

30
Q

Petroleum Ether

A
  • low boiling point
  • mainly hexanes and pentanes
  • more hydrophobic than diethyl ether and therefore selective for more hydrophobic lipids
31
Q

Three ways for Dry extraction?

A

Discontinuous Extraction
Intermittent Extraction
Continuous Extraction

32
Q

What is disconinuous extraction

A

high ratio of organic solvent sample

33
Q

What is intermittent extraction

A

Solvent is in contact with sample intermittently (soxhlet)

34
Q

What is continuous extraction?

A

solvent is always in contact with the sample for given period of time (Goldfish)

35
Q

How do you avoid lipid oxidation?

A

Using inert atmosphere
Preparing smaple under low temp
Avoiding excessive light

36
Q

Steps in sample preparation of wet analysis

A

Removal of water: To enhance penetration of non-polar solvents
Reduction of particle size: Grinding (of nuts) enhances surface area
Separation of the lipid from bound proteins and/or carbohydrates through the use of alkaline or acid hydrolysis

37
Q

Describe the importance of acid hydrolysis in wet extraction. (2 reasons)

A

Enable penetration of solvent into the sample
Break both covalently and ionically bound lipids into easily extractable lipid forms

Meat sample–(hydrolysis by HCl)–> Solvent extraction for crude fat

38
Q

What are the lipid in dairy, bread, flour and animal products like? Is direct extraction efficient?

A

Bound to proteins and carbohydrates and direct extraction with non polar solvents is inefficient

39
Q

What is discontinuous extraction

A

Simplest version of extraction
No continuous flow of solvent
Sample is extracted with fixed volume of solvent

40
Q

What are the disadvantages of discontinuous extraction

A 
Needs large amount of solvent
Low efficiency (as solvent extracts the fat, its ability to extract fat decreases)
41
Q

What is intermittent extraction?

A

semi continuous solvent

soxhlet extraction

42
Q

What is the soxhlet instrument?

A

Consist of a flask (2) for holding the solvent (1), a section containing the siphoning unit (Soxhelt flask) (6, 7), paper thimble for holding food (4), and a condenser (9).

43
Q

What are the 2 main components of Soxhelt apparatus that contain the sample and the solvent?

A

Soxhelt flask and paper thimble

44
Q

Soxhlet extraction steps?

A

The sample is placed in filter paper thimble.
2. The solvent builds up in the extraction chamber.
3. The solvent accumulates in the extraction chamber
(soxhelt flask) for 5-10 mins that facilitate the extraction
of crude fat from the sample.
4. The solvent+crude fat siphons back to the boiling flask.
5. Dismantle the unit, place the bottom flask containing solvent and fat on a heating mantle and evaporate the solvent to obtain crude fat
6. Measure the crude fat (weight or volume) left in the flask.

45
Q

What are some variables that need to be considered with crude fat determination?

A

Sample preparation
Choice of solvent (petroleum and diethyl ether)
Extraction ( temp, time and particle size)

46
Q

What is continuous extracton method?

A

Goldfish method

47
Q

What is the goldfish method?

A

Based on closed loop of solvent evaporating being condensed

  • Procedure onvolves placing the sample between boiling solvent and cold surface
  • Solvent from boiling flask (Baker) continuously flows over the sample place in a ceramic thimble
  • Boilin continues, teh solvent vaporizes, condenses on the cold surfaces and washed back through the sample to the boilding falsk
48
Q

What are the limitations of goldfish?

A

Channeling-formation of solvent channel in the sample and fire hazard

49
Q

What happens to the solvent in goldfish extraction?

A

Solvent condenses and flows over the sample
The solvent also evaporates
The sample tube collects the sample in the sample tube

50
Q

What are the most important wet extraction methods? (3)

A

Babcock and Gerber
Majonner
Bligh and Dyer

51
Q

What is the Babcock Method

A

Non solvent wet extraction

  • measure total lipids
  • Sample contain water
  • It is still recognized as a reference method for milk fat
52
Q

What is the principle?

A

Wet sample + H2SO4 + heat -> Centrifugation -> Fat coalesces/ (blob) of fat measured Volumetrically by the graduated portion of the Babcock bottle.
H2SO4 digests protein to liberate the fat, generates heat and releases the fat.
Total fat is measured volumetrically
It is not applicable to products containing chocolate or added sugar without modification because of charring of chocolate and sugar by sulfuric acid.

53
Q

What is the Gerber MEthod?

A

Non solvent wet extraction
Similar to babcock
Besides H2SO4, isoamyl alcohol added to prevent the charring of sugar
Help releasing lipid from organic material

54
Q

Majonnier Method (Base/alkaline method)

A

Can be used for liquid and solid milk samples

55
Q

What is the principle of the Majonnier method

A 
NH4OH 
Ethanol
\+
Petroleum Ether
Diethyl ether
-->
Centrifugation
- Decant ether solution into previously weighed dish
-->
Evaporation
--> 
Majonnier Fat Dish
56
Q

What are the 4 regaents of Majonnier method?

A

1-NH4OH dissolves protein of casein micelle membrane and fat globule membrane to separate any bond lipids from proteins; if the sample is sour, it neutralizes the acidic sample.
2-Ethanol prevents milk from becoming viscous (prevents possible gel formation).
3-Diethyl ether and Petroleum ether solubilize and extract fat;

57
Q

What prevents absorption of water by diethyl ether and dissolves non plar lipids?

A

Mix of petroleum ether with diethyl ether

58
Q

What is the Bligh and Dyer MEthod mainly used for?

A

Initially used for fish and seafood–> now for meat and meat products

59
Q

What is the principle of the Bligh and dyer method?

A

Extraction of lipids with a mixture of Chloroform: Methanol: Water
Monophasic to biphasic state

60
Q

What is the method of bligh and dyer?

A

Food samples are mixed/homogenized in a chloroform-methanol solution (CHCl3) and the homogenized mixture is filtered into a collection tube.
•A 0.88 % potassium chloride (KCl) aqueous solution is added to the chloroform-methanol mixture containing the extracted fats to form two phases: the aqueous phase (top) and the chloroform phase containing the lipid (bottom).
•The phases are further separated in a separatory funnel or by centrifugation.
•Evaporation of the chloroform, to quantify total fat by weight.

61
Q

What are other instrumental methods?

A

Infrared Method: fat can absorb IR energy at a wavelength 3.73μm;
2-Specific Gravity (Foss-Let Method):
Fat is determined as a function of the specific gravity of a sample solvent extract.
3-Nuclear Magnetic Resonance (NMR).

62
Q

Flow path of bligh-dyer method

A

sample–> extraction fat by monophasic (extractio solvent)–> Add CHCl3 or water to change to biphsic state–> Aq phase containes non fat materials and CHCl3 contains FAT –> Seperation by separatory funnel–> remove CHCl3

63
Q

Which sample would have a higher fat content: once with higher or lower E absorption? (IR method)

A

Higher

64
Q

What is the standard method of milk analysis?

A

Gerber method

65
Q

What is added to prevent charring of sugar in wet extractions of fat in samples containing high CHO?

A

isoamyl alcohol

66
Q

What 2 methods are discontinuous solvent extractions?

A

Majonnier

Bligh and Dyer

5) FDSC 300 (14 decks)

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