Lecture 7 - Fat Analysis Flashcards
define a lipid
soluble in organic solvents; insoluble or sparingly soluble in water
define total fat according to the FDA
sum of fatty acids from C4 to C24 calculated as triglycerides
difference between oils and fats?
oils = liquid at room temp fats = solids at room temp
what are the 3 classes of lipids?
simple lipids, compounds lipids, derived lipids
list examples of simple lipids
- fats
- waxes
they are esters of fatty acids with alcohols
list examples of compound lipids
- phospholipids
- cerebrosides
- sphingolipids
they are compounds containing groups in addition to an ester of a fatty acid with an alcohol
list examples of derived lipids
- fatty acids
- long chain alcohols
- sterols
- fat-soluble vitamins
- hydrocarbons
substances derived from neutral lipids or compound lipids
why is it important to measure fat content in food materials?
- nutritional evaluation
- health/diet restrictions
- food quality (mouthfeel/texture)
- economic consideration
what unique property of lipids can be exploited for their analysis?
level of insolubility in water
what lipids are found in foods?
- triglycerides
- free fatty acids
- phospholipids
- monoglycerides
- diglycerides
- sterols
- complex lipids
- waxes
what is crude fat?
nonpolar lipids only (TG)
how do you find crude fat?
dry extraction techniques
Soxhlet and Goldfish methods
what is total lipids?
nonpolar AND polar lipids (eg: TG and phospholipids in milk)
how do you find total lipids?
wet extraction techniques
Babcock, Gerber, Mojonnier, Bligh & Dyer
what are the dry extraction techniques?
Soxhlet, Goldfish
what are the wet extraction techniques?
Babcock, Mojonnier, Bligh & Dyer
what techniques utilize solvent extraction?
Soxhlet, Goldfish, Mojonnier, Bligh & Dyer
what techniques are non-solvent extracting?
Babcock, Gerber
which method is intermittent?
Soxhlet
which method is continuous?
Goldfish
which methods are discontinuous?
Mojonnier, Bligh & Dyer
the extraction of food material by a nonpolar solvent will give an estimate of _____ fat
crude
crude fat measures mainly the _____ which in many foods represent more than 95% of total lipids
triglycerides
describe the general procedure of a dry extraction technique
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
ideal solvent properties. go!
- 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
the boiling point of an extracting solvent should be (high/low)
low
list examples of nonpolar organic solvents used for extraction
- hydrocarbons (hexane, heptane, pentane, petroleum ether)
- diethyl ether (can explode)
- n-Butanol
what is petroleum ether?
- mixture of hexanes and pentanes
- low boiling point (35-38C)
- more hydrophobic than diethyl ether
discontinuous extraction has a (high/low) ratio of organic solvent to sample
high
what’s intermittent extraction?
solvent is in contact with sample intermittently
what is continuous extraction?
solvent is always in contact with the sample for a period of time
what are the general steps for sample prep?
1) remove water
2) reduce particle size (grind)
3) separation of lipid from bound proteins and/or CHO by alkaline or acid hydrolysis
what does acid hydrolysis accomplish?
- penetration of solvent into sample
- breaking of covalently and ionically bound lipids to easily extractable forms
discontinuous extraction extracts fats from a sample with a _____ volume of solvent
fixed
limitations of discontinuous extraction?
- needs large amount of solvent
- low efficiency (as solvent extracts fat, its ability to keep extracting decreases)
describe a Soxhlet instrument
- flask holds solvent
- siphoning unit
- paper thimble holds food
- condenser
what are the steps of soxhlet extraction?
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
what variables should be considered during crude fat determination?
- sample prep
- choice of solvent
- extraction (time, temp, particle size)
the goldfish method is based on a _____ _____ of solvent evaporating and being condensed
closed loop
what is the biggest limitation of the Goldfish method?
formation of a solvent channel in the sample (fire hazard)
what makes a method a “dry” or “wet” method?
presence (wet) or absence (dry) of polar solution
babcock method is a (dry/wet) extraction
wet (nonsolvent)
babcock method measures _____ fat
total
true or false: a sample used for babcock extraction must contain water
true
which method is primarily used for determining milk fat?
Babcock method
describe the Babcock method
- 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
limitation of babcock method?
sulfuric acid can char sugar and chocolate. not suitable for chocolate or added sugar products.
gerber method is a _____ extraction
wet (nonsolvent)
describe the gerber method
- H2SO4 AND isoamyl alcohol is added to wet sample in the presence of heat
- centrifugation
- fat blob is measured volumetrically
what does the addition of isoamyl alcohol do? what method am i talking about?
method: gerber
purpose: prevents charring of sugar
what kind of food commodities are suitable for the Mojonnier method?
milk, dairy products, fish, meat
describe the Mojonnier method
- 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
why use petroleum ether for the Mojonnier method?
prevents absorption of water by diethyl ether and dissolves more nonpolar lipids
what food commodities are suitable for the Bligh and Dyer method?
fish and seafoods, meat and meat products
what reagents are used in the Bligh and Dyer method?
Chloroform, methanol, and water
describe the Bligh and Dyer method
- 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
what instrumental methods are there for fat determination?
- IR method
- Specific Gravity (Foss-Let Method)
- Nuclear Magnetic Resonance
what’s the IR method?
fat can absorb IR energy at wavelength 3.73 um; the more the energy absorption, the higher the fat content
