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Analysis of Lipids 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
REFRACTIVE INDEX
Values vary with degree and type of unsaturation, oxidation, heat treatment and fat content
26
Smoke point
Temp at which the sample begins to smoke
27
Flash point
Temp at which a flash (spark) appears at any point of the surface of the sample
28
Fire point
Temp at which the evolution of volatiles supports continuous combustion
29
Cold test
Measure of resistance to crystallization
30
Cloud point
Temp at which a cloud is formed in a liquid fat due to the beginning of crystallization
31
Melting point
Melt over a range of temps Fats pass through a gradual softening before they become totally liquid
32
Capillary tube MP
Heat a beaker with mineral oil Thermometer and capillary tube with sample in the beaker Determine which temp the fat is totally melted
33
Dropping point
Sample heats up and melts Determine temp at which the sample goes into a tube Use laser to find T drip
34
DSC
Determine melting profile of fats and oils Characterize hardness, polymorphic, thermal behavior
35
DSC helps you find
Temp where lipid starts to melt Temp where lipid is melted Temp where lipid starts to crystallize Temp where lipid is crystallized
36
Solid fat content/index
Determine relative % of solid fat and liquid oil as a function of T Quality factor for shortening/spread Increase hydrogenation = higher SFC
37
Iodine Value
Measure of unsaturation of FA Higher unsaturation = more iodine absorbed Halogen addition to double bonds Titration with sodium thiosulfate
38
Iodine value used to
Characterize oils Follow hydrogenation Indicate lipid ox
39
Saponification value
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
Phosphorus content
Determine the amount of hydration water used to degum crude oils
41
Acid value
Amount of FFA in a fat Amount of KOH needed to neutralize FFA in 1g of fat/oil
42
Rancidity
Off odors and flavors from lipolysis or fat oxidation
43
Lipolysis
Hydrolysis of FA TG --> FFA + Glycerol
44
Hydrolytic rancidity
Catalyzed by lipases Rancid, goat flavor, soapy
45
Oxidative rancidity
Off flavors and odors Peroxides, hydroperoxides Cardboardy, paint, bitter
46
Oxidation
Reaction of O2 with double bonds in FA chains
47
Controlling oxidative rancidity
Control amount of unsat FA Control [Oxygen] Remove metal catalysts Limit UV exposure Control temp
48
Peroxide value
Meausure of the peroxide lipid products that will oxidize KI mEq of peroxide / kg fat PV > 20 = highly oxidized
49
Anisidine value
Amount of aldehydes in a sample Aldehydes react w/ p anisidne to form a yellow color
50
Totox value
Anisidine value + 2x Peroxide value Rises continually during oxidation Total oxidation of fat
51
TBA Test
Measures secondary oxidation product (malondialdehyde) Creates a colored compound
52
Oil stability index
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
Lipid fractionation
TLC uses silica plates Lipids separate by size, polarity
54
FA analysis
Determine by quantifying type and amount of FA Gas chromatography TG/phospholipids saponified FFA --> FA methyl esters
55
Trans FA
Separated using special GC columns Can use IR
56
TG composition
High temp GC HPLC
57
Quantify cholesterol
GC HPLC
58
HPLC
Separate based on chemistry Authenticity of oils Identify of species of TG

Food Analysis (19 decks)

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