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Food Analysis > Analysis of Lipids > Flashcards

Analysis of Lipids Flashcards

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Gourmet Food flashcards
1
Q

Lipids

A

Soluble in organic solvents
Rarely soluble in water

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2
Q

Lipid importance

A

Nutritional labeling
Standard of identity
Function and nutritional properties

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3
Q

Crude fat analysis

A

Total lipid content determined via extraction

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4
Q

Sample prep

A

Pre drying
Particle size reduction
Acid hydrolysis

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5
Q

Ideal solvent

A

Extract fat efficiently (high solvent power)
Don’t extract proteins or carbs (low solvent power)
Evaporates readily
Leaves no residue
Nontoxic
Nonflammable
Inexpensive
Non hygroscopic (doesn’t take up water)

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6
Q

Ethyl ether

A

Expensive
Absorbs water
Forms peroxides
Fire, explosion hazard
Very good solvent for fat

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7
Q

Petroleum ether

A

Not an ether (chemically)
Pentane + hexane
More hydrophobic than ethyl
Absorbs less water
Less flammable

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8
Q

Continous extraction

A

Solvent continuously flows over the sample
Solvent always in contact with solute
Goldfish method

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9
Q

Semicontinuous method

A

Solvent builds up in extraction chamber
Then siphons back into boiling flask
Soxhlet

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10
Q

Discontinuous method

A

Does not require prior removal of moisture
Mojonnier

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11
Q

Goldfisch method

A

Sample constantly in contact with solvent
Reduce amount of time of extraction

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12
Q

Goldfish disadvantage

A

Channeling
Take certain routes though the sample, leaves parts untouched
Inefficient

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13
Q

Soxhlet

A

Solvent builds up in chamber, then siphons back down
Soaking effect
No channeling

Takes longer than Goldfisch

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14
Q

Mojonnier

A

Extracted with ethyl ether + petroleum ether
Centrifuge + extract 3x

Ether extract decanted into dish
Solvent evaporated in a hot plate

Developed for dairy foods

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15
Q

Folch extraction

A

Combine chloroform and methanol
Low fat samples
Generate samples for subsequent FA analysis

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16
Q

Babcock Test

A

Add H2SO4 to milk to digest protein and release fat

Centrifuge and incubate
Measure volumetrically

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17
Q

Babcock foods

A

Milk and dairy products

Not for products with chocolate or added sugar (charring)

Essential oil in flavor extracts
Fat in seafood

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18
Q

Instrumental methods

A

Rapid
Nondestructive
Min sample prep

Expensive
Need calibration curve

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19
Q

IR

A

More NRG absorbed = higher fat

Mid IR for milk fat

Near IR for meat, cereal, oilseed

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20
Q

NMR

A

Meat, snacks, dairy

Moisture needs to be removed 1st

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21
Q

NMR Pros

A

Nondestructive
Short analysis time
Min sample prep
No solvent

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22
Q

Compositional analysis

A

TAG
FA profile
Trans isomers

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23
Q

Physical properties

A

Color
MP
smoke point
Consistency

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24
Q

Chemical tests

A

Acid value
Saponification value
Peroxide value
Oxidative stability

25
Q

REFRACTIVE INDEX

A

Values vary with degree and type of unsaturation,
oxidation, heat treatment and fat content

26
Q

Smoke point

A

Temp at which the sample begins to smoke

27
Q

Flash point

A

Temp at which a flash (spark) appears at any point of the surface of the sample

28
Q

Fire point

A

Temp at which the evolution of volatiles supports continuous combustion

29
Q

Cold test

A

Measure of resistance to crystallization

30
Q

Cloud point

A

Temp at which a cloud is formed in a liquid fat due to the beginning of crystallization

31
Q

Melting point

A

Melt over a range of temps
Fats pass through a gradual softening before they become totally liquid

32
Q

Capillary tube MP

A

Heat a beaker with mineral oil

Thermometer and capillary tube with sample in the beaker

Determine which temp the fat is totally melted

33
Q

Dropping point

A

Sample heats up and melts
Determine temp at which the sample goes into a tube
Use laser to find T drip

34
Q

DSC

A

Determine melting profile of fats and oils
Characterize hardness, polymorphic, thermal behavior

35
Q

DSC helps you find

A

Temp where lipid starts to melt
Temp where lipid is melted
Temp where lipid starts to crystallize
Temp where lipid is crystallized

36
Q

Solid fat content/index

A

Determine relative % of solid fat and liquid oil as a function of T

Quality factor for shortening/spread

Increase hydrogenation = higher SFC

37
Q

Iodine Value

A

Measure of unsaturation of FA

Higher unsaturation = more iodine absorbed
Halogen addition to double bonds
Titration with sodium thiosulfate

38
Q

Iodine value used to

A

Characterize oils
Follow hydrogenation
Indicate lipid ox

39
Q

Saponification value

A

Number of mg of KOH it takes to saponify 1g of fat

Fat –> glycerol + FA
Indication of avg MW of fat

Lower saponification value = longer chain length

40
Q

Phosphorus content

A

Determine the amount of hydration water used to degum crude oils

41
Q

Acid value

A

Amount of FFA in a fat
Amount of KOH needed to neutralize FFA in 1g of fat/oil

42
Q

Rancidity

A

Off odors and flavors from lipolysis or fat oxidation

43
Q

Lipolysis

A

Hydrolysis of FA
TG –> FFA + Glycerol

44
Q

Hydrolytic rancidity

A

Catalyzed by lipases
Rancid, goat flavor, soapy

45
Q

Oxidative rancidity

A

Off flavors and odors
Peroxides, hydroperoxides
Cardboardy, paint, bitter

46
Q

Oxidation

A

Reaction of O2 with double bonds in FA chains

47
Q

Controlling oxidative rancidity

A

Control amount of unsat FA
Control [Oxygen]
Remove metal catalysts
Limit UV exposure
Control temp

48
Q

Peroxide value

A

Meausure of the peroxide lipid products that will oxidize KI

mEq of peroxide / kg fat
PV > 20 = highly oxidized

49
Q

Anisidine value

A

Amount of aldehydes in a sample
Aldehydes react w/ p anisidne to form a yellow color

50
Q

Totox value

A

Anisidine value + 2x Peroxide value
Rises continually during oxidation
Total oxidation of fat

51
Q

TBA Test

A

Measures secondary oxidation product (malondialdehyde)
Creates a colored compound

52
Q

Oil stability index

A

Determine induction period
Done by bubbling air through oil or fat at high temp
Purposely oxidize sample
Measure the conductivity of the air (aldehydes increase conductivity)

53
Q

Lipid fractionation

A

TLC uses silica plates
Lipids separate by size, polarity

54
Q

FA analysis

A

Determine by quantifying type and amount of FA
Gas chromatography

TG/phospholipids saponified
FFA –> FA methyl esters

55
Q

Trans FA

A

Separated using special GC columns
Can use IR

56
Q

TG composition

A

High temp GC
HPLC

57
Q

Quantify cholesterol

A

GC
HPLC

58
Q

HPLC

A

Separate based on chemistry
Authenticity of oils
Identify of species of TG

Food Analysis (19 decks)

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