Analysis of Lipids Flashcards
Lipids
Soluble in organic solvents
Rarely soluble in water
Lipid importance
Nutritional labeling
Standard of identity
Function and nutritional properties
Crude fat analysis
Total lipid content determined via extraction
Sample prep
Pre drying
Particle size reduction
Acid hydrolysis
Ideal solvent
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)
Ethyl ether
Expensive
Absorbs water
Forms peroxides
Fire, explosion hazard
Very good solvent for fat
Petroleum ether
Not an ether (chemically)
Pentane + hexane
More hydrophobic than ethyl
Absorbs less water
Less flammable
Continous extraction
Solvent continuously flows over the sample
Solvent always in contact with solute
Goldfish method
Semicontinuous method
Solvent builds up in extraction chamber
Then siphons back into boiling flask
Soxhlet
Discontinuous method
Does not require prior removal of moisture
Mojonnier
Goldfisch method
Sample constantly in contact with solvent
Reduce amount of time of extraction
Goldfish disadvantage
Channeling
Take certain routes though the sample, leaves parts untouched
Inefficient
Soxhlet
Solvent builds up in chamber, then siphons back down
Soaking effect
No channeling
Takes longer than Goldfisch
Mojonnier
Extracted with ethyl ether + petroleum ether
Centrifuge + extract 3x
Ether extract decanted into dish
Solvent evaporated in a hot plate
Developed for dairy foods
Folch extraction
Combine chloroform and methanol
Low fat samples
Generate samples for subsequent FA analysis
Babcock Test
Add H2SO4 to milk to digest protein and release fat
Centrifuge and incubate
Measure volumetrically
Babcock foods
Milk and dairy products
Not for products with chocolate or added sugar (charring)
Essential oil in flavor extracts
Fat in seafood
Instrumental methods
Rapid
Nondestructive
Min sample prep
Expensive
Need calibration curve
IR
More NRG absorbed = higher fat
Mid IR for milk fat
Near IR for meat, cereal, oilseed
NMR
Meat, snacks, dairy
Moisture needs to be removed 1st
NMR Pros
Nondestructive
Short analysis time
Min sample prep
No solvent
Compositional analysis
TAG
FA profile
Trans isomers
Physical properties
Color
MP
smoke point
Consistency
Chemical tests
Acid value
Saponification value
Peroxide value
Oxidative stability
REFRACTIVE INDEX
Values vary with degree and type of unsaturation,
oxidation, heat treatment and fat content
Smoke point
Temp at which the sample begins to smoke
Flash point
Temp at which a flash (spark) appears at any point of the surface of the sample
Fire point
Temp at which the evolution of volatiles supports continuous combustion
Cold test
Measure of resistance to crystallization
Cloud point
Temp at which a cloud is formed in a liquid fat due to the beginning of crystallization
Melting point
Melt over a range of temps
Fats pass through a gradual softening before they become totally liquid
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
Dropping point
Sample heats up and melts
Determine temp at which the sample goes into a tube
Use laser to find T drip
DSC
Determine melting profile of fats and oils
Characterize hardness, polymorphic, thermal behavior
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
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
Iodine Value
Measure of unsaturation of FA
Higher unsaturation = more iodine absorbed
Halogen addition to double bonds
Titration with sodium thiosulfate
Iodine value used to
Characterize oils
Follow hydrogenation
Indicate lipid ox
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
Phosphorus content
Determine the amount of hydration water used to degum crude oils
Acid value
Amount of FFA in a fat
Amount of KOH needed to neutralize FFA in 1g of fat/oil
Rancidity
Off odors and flavors from lipolysis or fat oxidation
Lipolysis
Hydrolysis of FA
TG –> FFA + Glycerol
Hydrolytic rancidity
Catalyzed by lipases
Rancid, goat flavor, soapy
Oxidative rancidity
Off flavors and odors
Peroxides, hydroperoxides
Cardboardy, paint, bitter
Oxidation
Reaction of O2 with double bonds in FA chains
Controlling oxidative rancidity
Control amount of unsat FA
Control [Oxygen]
Remove metal catalysts
Limit UV exposure
Control temp
Peroxide value
Meausure of the peroxide lipid products that will oxidize KI
mEq of peroxide / kg fat
PV > 20 = highly oxidized
Anisidine value
Amount of aldehydes in a sample
Aldehydes react w/ p anisidne to form a yellow color
Totox value
Anisidine value + 2x Peroxide value
Rises continually during oxidation
Total oxidation of fat
TBA Test
Measures secondary oxidation product (malondialdehyde)
Creates a colored compound
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)
Lipid fractionation
TLC uses silica plates
Lipids separate by size, polarity
FA analysis
Determine by quantifying type and amount of FA
Gas chromatography
TG/phospholipids saponified
FFA –> FA methyl esters
Trans FA
Separated using special GC columns
Can use IR
TG composition
High temp GC
HPLC
Quantify cholesterol
GC
HPLC
HPLC
Separate based on chemistry
Authenticity of oils
Identify of species of TG
