Lecture 7 - Fat Analysis

Question 1

def of lipid?
FDA def?

Answer 1

soluble in organic solvents but insoluble in water

FDA: total fat is the sum of FA from C4 to C24 calculated as triglycerides

Question 2

oils vs fats?

Answer 2

oils: TG that are liquid at room temp
fats: solid at room temp

Question 3

what is a simple lipid

Answer 3

ester of FA with alcohol

ie fats and waxes

Question 4

what is a compound lipid

Answer 4

compounds containing groups in addition to an ester of a FA with an alcohol

ie phospholipids, sphongolipids

Question 5

what is a derived lipid

Answer 5

substance derived from neutral lipids or compound lipids

ie FA, long chain alcohols, sterols

Question 6

importance of measuring fat content in food?

Answer 6

1. nutrition
2. health/diet restrictions
3. food quality (mouth feel)
4. economic consideration

Question 7

the ___ of lipids in water makes them separate from proteins and carbohydrates in foods

Answer 7

insolubility

Question 8

lipids have a wide range of relative ___ depending on their molecular constituents

Answer 8

hydrophobicity

Question 9

what is crude fat?

how is it extracted?

Answer 9

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)

Question 10

total lipids represent ____ and ___ lipids.

how are total lipids extracted?

Answer 10

nonpolar; polar

extracted by wet extraction techniques (babcock, majonnier, bligh and dyer methods)

Question 11

what are the 2 dry extraction methods (for crude fat)

Answer 11

1. soxhelt

2. goldfish

Question 12

what are the 3 wet extraction methods

Answer 12

1. babcock
2. majonnier
3. bligh and dyer

Question 13

what are the 4 solvent extraction methods?

Answer 13

1. soxhelt
2. goldfish
3. majonnier
4. bligh and dyer

Question 14

what are the 2 non solvent extractions?

Answer 14

1. babcock

2. gerber

Question 15

the extraction of food material by a non polar solvent will give an estimate of ___ but not of ____

Answer 15

crude fat

total lipids

Question 16

the major component of lipids in food is ___. Crude fat measures mainly the ____ which represents more than 95% of total lipids

Answer 16

TG

Question 17

steps of determination of crude fat?

Answer 17

1. dry food sample is extracted by a non polar organic solvent to a solution of fat in the solvent
2. solution of fat is evaporated to the residue (crude fat)

Question 18

what are 3 non polar organic solvents used for extracting solvents for crude fat determiniation?

Answer 18

1. hydrocarbons: eg hexane, heptane, pentane. Most common
2. diethyl ether. absorbs O2 and forms peroxides which will explode with heat
3. n-butanol: most polar

Question 19

what kind of solvent is used in the extraction step in determining crude fat?

Answer 19

non polar organic solvents

because you want to extract non polar materials, mainly TGs

Question 20

what are the 3 basic ways of carrying out the dry extraction? How are they different from each other?

Answer 20

1. discoutinous extraction: high ratio of organic solent to sample
2. intermitten extraction: solvent is in contact with the sample intermittently (eg soxhlet)
3. continuous extraction: solvent is always in contact with the sample (eg goldfish)

Question 21

pros and cons of discontinuous extraction?

Answer 21

pros

• simplest dry extraction method
• no continuous flow of solvent

cons

• needs large amount of solvent (1 sample: 10 solvent)
• low efficiency

Question 22

what are the steps of soxhelt extraction?

Answer 22

1. place sample in filter paper thimblr
2. solvent builds up in extraction chamber and surrounds the sample
3. solvent and fat siphons back to boiling flash
4. remove solvent. fat obtained is measured

Question 23

what are variables that need to be considered in determining crude fat?

Answer 23

1. sample preparation (dried sample)
2. choice of solvent
3. extraction (temp, time, particle size)

Question 24

describe the goldfish method of continuous extraction

Answer 24

• 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

Question 25

what are the most important wet extraction methods?

Answer 25

1. non-solvent wet extraction: babcock and gerber method 2. solvent wet extraction: majonnier method 3. solvent wet extraction: bligh and dyer method

Question 26

describe the babcock method

Answer 26

- non solvent wet extraction - measures total lipids in samples containing water (ie dairy) - recognized as a reference method for milk fat

Question 27

steps in the babcock method? role of H2SO4? what is this method not applicable to?

Answer 27

1. wet sample + H2SO4 is heated 2. centrifugation 3. 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

Question 28

difference of gerber method and babcock method?

Answer 28

besides H2SO4, isoamyl alcohol is added to prevent charring of sugar (in gerber method). This helps released lipid from carbohydrates

Question 29

what is the mojonnier method used for? steps?

Answer 29

-milk, dairy, fish, meat 1. milk is treated with NH4OH and ethanol 2. petroleum and diethyl ether 3. centrifugation 4. evaporation

Question 30

4 reagents required in the mojonnier method?

Answer 30

1. NH4OH: dissolves protein of casein micelle membrane to separate bond lipids from proteins. If sample is sour, it neutralizes the acid 2. ethanol: prevents milk from becoming viscous (prevents gel formation) 3. diethyl ether and petroleum ether: solubilizes and extracts fat. PRevents absorption of water by diethyl ether. Dissolves more nonpolar lipids

Question 31

describe the bligh and dyer method what reagents are used to extract lipids? reagents can exist as ___ and ___

Answer 31

- 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)

Question 32

instrumental methods in fat analysis

Answer 32

1. infrared method: fat absorbs IR energy. more energy absorption = higher fat content of the sample 2. specific gravity (foss-let method): fat is determined as a function of the specific gravity of a sample solvent extract 3. nuclear magnetic resonance (NMR)