5. Analytical methods for fat and oil characterization
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4 analytical methods for fats and oils characterization?
• saponification value • iodine value • gas chromatographic analysis for FA composition • liquid chromatography
What is saponification?
hydrolysis of ester under alkaline conditions
how is saponification value defined?
number of milligrams of potassium hydroxide (KOH) required to neutralize FA resulting from complete hydrolysis of 1 g of sample
5 steps to determine saponification value? + formula
• weight 5g of fat • add 50 mL of KOH (0.5 N) • boil to sponify fat • titrate with HCl (0.5 N) using phenolphthalein indicator • 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
formula to calculate average molecular weight of TG
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
Formula to mathematically determine saponification value
16 800 (3 x 5600)/ 41 + [3 x ( sum XRi * MWFARi - 1)]
Why does cottonseed oil (oleic-linoleic group) have smaller SV than coconut oil (lauric group)?
• cottonseed –> longer FA (C18) –> divide by bigger number = smaller SV • Coconut oil –> lauric (C12) –> divide by smaller number = bigger SV
define iodine value.
mass of iodine absorbed by 100 g of sample
higher iodine value = fat or oil?
oil!
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)
• animal fats • non-drying • semi-drying • drying
what is a drying oil?
highly unsaturated oil that hardens to a tough solid film after a period of exposure to air
Iodine value determined normally using whose method? what is their method?
Wijs or Hanus method - react FA with iodine chloride, then titrate excess unreacted iodine chloride in presence of starch indicator
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
15g C18:1 * 254g / 282g = number of grams of I2
6 steps for GC analysis
• quantitatively mix fat or oil with C21:0 (internal standard) • saponify sample (hydrolysis under basic condition) • convert FA to methyl esters (treatment with CH3ONa) • separate methyl esters by gas chromatography (100 m capillary column) • determine peak areas of FA (FA are identified by retention time) • compare peak area of internal standard to calculate concentrations (units of g per 100 g of fat)
why is C21:0 used as an internal standard in GC?
because C21:0 FA is never present in fats and oils (unlike C15 and C17 –> present in milk a bit)