Lecture 7 - Fat Analysis

Question 1

define a lipid

Answer 1

soluble in organic solvents; insoluble or sparingly soluble in water

Question 2

define total fat according to the FDA

Answer 2

sum of fatty acids from C4 to C24 calculated as triglycerides

Question 3

difference between oils and fats?

Answer 3

oils = liquid at room temp
fats = solids at room temp

Question 4

what are the 3 classes of lipids?

Answer 4

simple lipids, compounds lipids, derived lipids

Question 5

list examples of simple lipids

Answer 5

• fats
• waxes
  they are esters of fatty acids with alcohols

Question 6

list examples of compound lipids

Answer 6

• phospholipids
• cerebrosides
• sphingolipids
  they are compounds containing groups in addition to an ester of a fatty acid with an alcohol

Question 7

list examples of derived lipids

Answer 7

• fatty acids
• long chain alcohols
• sterols
• fat-soluble vitamins
• hydrocarbons
  substances derived from neutral lipids or compound lipids

Question 8

why is it important to measure fat content in food materials?

Answer 8

• nutritional evaluation
• health/diet restrictions
• food quality (mouthfeel/texture)
• economic consideration

Question 9

what unique property of lipids can be exploited for their analysis?

Answer 9

level of insolubility in water

Question 10

what lipids are found in foods?

Answer 10

• triglycerides
• free fatty acids
• phospholipids
• monoglycerides
• diglycerides
• sterols
• complex lipids
• waxes

Question 11

what is crude fat?

Answer 11

nonpolar lipids only (TG)

Question 12

how do you find crude fat?

Answer 12

dry extraction techniques

Soxhlet and Goldfish methods

Question 13

what is total lipids?

Answer 13

nonpolar AND polar lipids (eg: TG and phospholipids in milk)

Question 14

how do you find total lipids?

Answer 14

wet extraction techniques

Babcock, Gerber, Mojonnier, Bligh & Dyer

Question 15

what are the dry extraction techniques?

Answer 15

Soxhlet, Goldfish

Question 16

what are the wet extraction techniques?

Answer 16

Babcock, Mojonnier, Bligh & Dyer

Question 17

what techniques utilize solvent extraction?

Answer 17

Soxhlet, Goldfish, Mojonnier, Bligh & Dyer

Question 18

what techniques are non-solvent extracting?

Answer 18

Babcock, Gerber

Question 19

which method is intermittent?

Answer 19

Soxhlet

Question 20

which method is continuous?

Answer 20

Goldfish

Question 21

which methods are discontinuous?

Answer 21

Mojonnier, Bligh & Dyer

Question 22

the extraction of food material by a nonpolar solvent will give an estimate of _____ fat

Answer 22

crude

Question 23

crude fat measures mainly the _____ which in many foods represent more than 95% of total lipids

Answer 23

triglycerides

Question 24

describe the general procedure of a dry extraction technique

Answer 24

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

Question 25

ideal solvent properties. go!

Answer 25

- 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

Question 26

the boiling point of an extracting solvent should be (high/low)

Answer 26

low

Question 27

list examples of nonpolar organic solvents used for extraction

Answer 27

- hydrocarbons (hexane, heptane, pentane, petroleum ether) - diethyl ether (can explode) - n-Butanol

Question 28

what is petroleum ether?

Answer 28

- mixture of hexanes and pentanes - low boiling point (35-38C) - more hydrophobic than diethyl ether

Question 29

discontinuous extraction has a (high/low) ratio of organic solvent to sample

Answer 29

high

Question 30

what's intermittent extraction?

Answer 30

solvent is in contact with sample intermittently

Question 31

what is continuous extraction?

Answer 31

solvent is always in contact with the sample for a period of time

Question 32

what are the general steps for sample prep?

Answer 32

1) remove water 2) reduce particle size (grind) 3) separation of lipid from bound proteins and/or CHO by alkaline or acid hydrolysis

Question 33

what does acid hydrolysis accomplish?

Answer 33

- penetration of solvent into sample | - breaking of covalently and ionically bound lipids to easily extractable forms

Question 34

discontinuous extraction extracts fats from a sample with a _____ volume of solvent

Answer 34

fixed

Question 35

limitations of discontinuous extraction?

Answer 35

- needs large amount of solvent | - low efficiency (as solvent extracts fat, its ability to keep extracting decreases)

Question 36

describe a Soxhlet instrument

Answer 36

- flask holds solvent - siphoning unit - paper thimble holds food - condenser

Question 37

what are the steps of soxhlet extraction?

Answer 37

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

Question 38

what variables should be considered during crude fat determination?

Answer 38

- sample prep - choice of solvent - extraction (time, temp, particle size)

Question 39

the goldfish method is based on a _____ _____ of solvent evaporating and being condensed

Answer 39

closed loop

Question 40

what is the biggest limitation of the Goldfish method?

Answer 40

formation of a solvent channel in the sample (fire hazard)

Question 41

what makes a method a "dry" or "wet" method?

Answer 41

presence (wet) or absence (dry) of polar solution

Question 42

babcock method is a (dry/wet) extraction

Answer 42

wet (nonsolvent)

Question 43

babcock method measures _____ fat

Answer 43

total

Question 44

true or false: a sample used for babcock extraction must contain water

Answer 44

true

Question 45

which method is primarily used for determining milk fat?

Answer 45

Babcock method

Question 46

describe the Babcock method

Answer 46

- 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

Question 47

limitation of babcock method?

Answer 47

sulfuric acid can char sugar and chocolate. not suitable for chocolate or added sugar products.

Question 48

gerber method is a _____ extraction

Answer 48

wet (nonsolvent)

Question 49

describe the gerber method

Answer 49

- H2SO4 AND isoamyl alcohol is added to wet sample in the presence of heat - centrifugation - fat blob is measured volumetrically

Question 50

what does the addition of isoamyl alcohol do? what method am i talking about?

Answer 50

method: gerber purpose: prevents charring of sugar

Question 51

what kind of food commodities are suitable for the Mojonnier method?

Answer 51

milk, dairy products, fish, meat

Question 52

describe the Mojonnier method

Answer 52

- 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

Question 53

why use petroleum ether for the Mojonnier method?

Answer 53

prevents absorption of water by diethyl ether and dissolves more nonpolar lipids

Question 54

what food commodities are suitable for the Bligh and Dyer method?

Answer 54

fish and seafoods, meat and meat products

Question 55

what reagents are used in the Bligh and Dyer method?

Answer 55

Chloroform, methanol, and water

Question 56

describe the Bligh and Dyer method

Answer 56

- 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

Question 57

what instrumental methods are there for fat determination?

Answer 57

- IR method - Specific Gravity (Foss-Let Method) - Nuclear Magnetic Resonance

Question 58

what's the IR method?

Answer 58

fat can absorb IR energy at wavelength 3.73 um; the more the energy absorption, the higher the fat content