5. Analytical methods for fat and oil characterization

Question 1

4 analytical methods for fats and oils characterization?

Answer 1

• saponification value
• iodine value
• gas chromatographic analysis for FA composition
• liquid chromatography

Question 2

What is saponification?

Answer 2

hydrolysis of ester under alkaline conditions

Question 3

how is saponification value defined?

Answer 3

number of milligrams of potassium hydroxide (KOH) required to neutralize FA resulting from complete hydrolysis of 1 g of sample

Question 4

5 steps to determine saponification value? + formula

Answer 4

1. weight 5g of fat
2. add 50 mL of KOH (0.5 N)
3. boil to sponify fat
4. titrate with HCl (0.5 N) using phenolphthalein indicator
5. conduct blank (B) determination

Formula: SV = 56.1 (MW of KOH) x (B - S) x normality of HCl/g of sample
B = mL of HCl required by blank to reach phenolphthalein endpoint
S = mL of HCl required by sample to reach phenolphthalein endpoint

Question 5

formula to calculate average molecular weight of TG

Answer 5

AMW (TG) = 41 + 3x ((XR1 * MWFAR1 + XR2 * MWFAR2) - 1)
XR1 = mole fraction of FA R1 (from GC)
XR2 = mole fraction of FA R2 (from GC)
- actually, Sum of (XRi * MWFARi) for all the fatty acids

Question 6

Formula to mathematically determine saponification value

Answer 6

16 800 (3 x 5600)/ 41 + [3 x ( sum XRi * MWFARi - 1)]

Question 7

Why does cottonseed oil (oleic-linoleic group) have smaller SV than coconut oil (lauric group)?

Answer 7

• cottonseed –> longer FA (C18) –> divide by bigger number = smaller SV
• Coconut oil –> lauric (C12) –> divide by smaller number = bigger SV

Question 8

define iodine value.

Answer 8

mass of iodine absorbed by 100 g of sample

Question 9

higher iodine value = fat or oil?

Answer 9

oil!

Question 10

rank these fats/oils from smaller IV to bigger IV:
- drying oils (linseed, sunflower), non-drying oils (olive, almond), semi-drying oils (cottonseed, sesame, soya), animal fat (butter, lard)

Answer 10

1. animal fats
2. non-drying
3. semi-drying
4. drying

Question 11

what is a drying oil?

Answer 11

highly unsaturated oil that hardens to a tough solid film after a period of exposure to air

Question 12

Iodine value determined normally using whose method?
what is their method?

Answer 12

Wijs or Hanus method
- react FA with iodine chloride, then titrate excess unreacted iodine chloride in presence of starch indicator

Question 13

if you know that C18:1 represents 15% of the FA in a sample of 100g, what is its contribution to the total IV number? knowing that 1 mol I2 = 254g and 1 mol C18:1 is 282g

Answer 13

15g C18:1 * 254g / 282g = number of grams of I2

Question 14

6 steps for GC analysis

Answer 14

1. quantitatively mix fat or oil with C21:0 (internal standard)
2. saponify sample (hydrolysis under basic condition)
3. convert FA to methyl esters (treatment with CH3ONa)
4. separate methyl esters by gas chromatography (100 m capillary column)
5. determine peak areas of FA (FA are identified by retention time)
6. compare peak area of internal standard to calculate concentrations (units of g per 100 g of fat)

Question 15

why is C21:0 used as an internal standard in GC?

Answer 15

because C21:0 FA is never present in fats and oils (unlike C15 and C17 –> present in milk a bit)