Lecture 7 - Fat Analysis Flashcards
def of lipid? FDA def?
soluble in organic solvents but insoluble in water
FDA: total fat is the sum of FA from C4 to C24 calculated as triglycerides
oils vs fats?
oils: TG that are liquid at room temp
fats: solid at room temp
what is a simple lipid
ester of FA with alcohol
ie fats and waxes
what is a compound lipid
compounds containing groups in addition to an ester of a FA with an alcohol
ie phospholipids, sphongolipids
what is a derived lipid
substance derived from neutral lipids or compound lipids
ie FA, long chain alcohols, sterols
importance of measuring fat content in food?
- nutrition
- health/diet restrictions
- food quality (mouth feel)
- economic consideration
the ___ of lipids in water makes them separate from proteins and carbohydrates in foods
insolubility
lipids have a wide range of relative ___ depending on their molecular constituents
hydrophobicity
what is crude fat?
how is it extracted?
the residue obtained after removal of the non polar organic solvent used to extract a dried sample.
mainly non-polar lipids (TGs)
extracted by dry extraction techniques (soxhelt and goldfish method)
total lipids represent ____ and ___ lipids.
how are total lipids extracted?
nonpolar; polar
extracted by wet extraction techniques (babcock, majonnier, bligh and dyer methods)
what are the 2 dry extraction methods (for crude fat)
- soxhelt
2. goldfish
what are the 3 wet extraction methods
- babcock
- majonnier
- bligh and dyer
what are the 4 solvent extraction methods?
- soxhelt
- goldfish
- majonnier
- bligh and dyer
what are the 2 non solvent extractions?
- babcock
2. gerber
the extraction of food material by a non polar solvent will give an estimate of ___ but not of ____
crude fat
total lipids
the major component of lipids in food is ___. Crude fat measures mainly the ____ which represents more than 95% of total lipids
TG
steps of determination of crude fat?
- dry food sample is extracted by a non polar organic solvent to a solution of fat in the solvent
- solution of fat is evaporated to the residue (crude fat)
what are 3 non polar organic solvents used for extracting solvents for crude fat determiniation?
- hydrocarbons: eg hexane, heptane, pentane. Most common
- diethyl ether. absorbs O2 and forms peroxides which will explode with heat
- n-butanol: most polar
what kind of solvent is used in the extraction step in determining crude fat?
non polar organic solvents
because you want to extract non polar materials, mainly TGs
what are the 3 basic ways of carrying out the dry extraction? How are they different from each other?
- discoutinous extraction: high ratio of organic solent to sample
- intermitten extraction: solvent is in contact with the sample intermittently (eg soxhlet)
- continuous extraction: solvent is always in contact with the sample (eg goldfish)
pros and cons of discontinuous extraction?
pros
- simplest dry extraction method
- no continuous flow of solvent
cons
- needs large amount of solvent (1 sample: 10 solvent)
- low efficiency
what are the steps of soxhelt extraction?
- place sample in filter paper thimblr
- solvent builds up in extraction chamber and surrounds the sample
- solvent and fat siphons back to boiling flash
- remove solvent. fat obtained is measured
what are variables that need to be considered in determining crude fat?
- sample preparation (dried sample)
- choice of solvent
- extraction (temp, time, particle size)
describe the goldfish method of continuous extraction
- based on a closed loop of solvent evaporating, being condensed
1. place sample between the boiling solvent and a cold surface
2. solvent from a boiling flash flows over the sample in the ceramic thimble
3. as boiling continues, solvent vaporizes, condenses on the cold surfaces and washes back through the samples to the boiling flask
what are the most important wet extraction methods?
- non-solvent wet extraction: babcock and gerber method
- solvent wet extraction: majonnier method
- solvent wet extraction: bligh and dyer method
describe the babcock method
- non solvent wet extraction
- measures total lipids in samples containing water (ie dairy)
- recognized as a reference method for milk fat
steps in the babcock method?
role of H2SO4?
what is this method not applicable to?
- wet sample + H2SO4 is heated
- centrifugation
- fat blobs are measured volumetrically by the graduated portion of the babcock bottle
- H2SO4 digests protein to liberate the fat
- no applicable to products containing chocolate or added sugar b/c of charring of chocolate and sugar by sulfuric acid
difference of gerber method and babcock method?
besides H2SO4, isoamyl alcohol is added to prevent charring of sugar (in gerber method). This helps released lipid from carbohydrates
what is the mojonnier method used for?
steps?
-milk, dairy, fish, meat
- milk is treated with NH4OH and ethanol
- petroleum and diethyl ether
- centrifugation
- evaporation
4 reagents required in the mojonnier method?
- NH4OH: dissolves protein of casein micelle membrane to separate bond lipids from proteins. If sample is sour, it neutralizes the acid
- ethanol: prevents milk from becoming viscous (prevents gel formation)
- diethyl ether and petroleum ether: solubilizes and extracts fat. PRevents absorption of water by diethyl ether. Dissolves more nonpolar lipids
describe the bligh and dyer method
what reagents are used to extract lipids?
reagents can exist as ___ and ___
- solvent wet extraction method
- used for fish, seafood, meat
reagents: chloroform, methanol, water
reagents can exist as single phase (monophasic. used for extraction of lipids) and 2 phases (biphasic. used to separate lipids into the organic phase)
instrumental methods in fat analysis
- infrared method: fat absorbs IR energy. more energy absorption = higher fat content of the sample
- specific gravity (foss-let method): fat is determined as a function of the specific gravity of a sample solvent extract
- nuclear magnetic resonance (NMR)
