Analysis of dietary fats
HYDROPEROXiDES: MARKERS OF LIPID OXIDATION
The hydroperoxide content provides information on the level of oxidation of a fat at a given time. This content results from the amount of hydroperoxides produced from fatty acids, for a given amount of fat, and degraded into secondary oxidation products.
The peroxide value corresponds to the measured amount of oxygen that is chemically bonded to a fat in the form of peroxides, particularly hydroperoxides.
The peroxide value (PV) can be expressed in milliequivalents of active oxygen per kg of fat, or in mmoles of active oxygen per kg of fat. It can also be used to calculate the hydroperoxide content in moles per kg of fat.
HYDROPEROXIDES: MARKERS OF LIPID OXIDATION
PrincipleThe determination of a peroxide value is based on the solubilization of fat in a solvent (isooctane/glacial acetic acid) and the addition of potassium iodine. The diiodine produced in such a way is titrated with a sodium thiosulfate solution.
R-O-O-H + 2 I- + 2 H+ → R-O-H + I2 + H20
I2 + 2 S2032- → 2 I- + S4062-
with R-O-O-H a lipid hydroperoxide
Method adapted from the NF EN ISO 3960 standard ("peroxide value") and the AOCS Official Method Cd 8-53
HYDROPEROXIDES: MARKERS OF LIPID OXIDATION
Equipment & Reagents
- Standard laboratory equipment, in particular: analytical scale, magnetic stirrer, burette, glassware.
- Glacial acetic acid/Isooctane (3/2, v/v)
- Potassium iodine solution saturated at 175g/100mL (to be prepared extemporaneously)
- Starch solution (mix 5 g of soluble starch with 30 mL of water and add the mixture to 1 L of boiling water; boil for 3 mins, then allow to cool).
- Sodium thiosulfate at 0.01 mol/L and 0.001 mol/L (aqueous solutions)
Method adapted from the NF EN ISO 3960 standard ("peroxide value") and the AOCS Official Method Cd 8-53
HYDROPEROXIDES: MARKERS OF LIPID OXIDATION
Experimental procedure- Accurately weigh 0.5 g of fat in a 250 mL Erlenmeyer flask and solubilize in a mixture of glacial acetic acid/isooctane (3/2, v/v).
- Add 1 mL of the saturated potassium iodine solution and carefully mix it with a magnetic stirrer for precisely 1 minute.
- Leave it in the dark for 5 minutes.
- Add 75 mL of distilled water and 1 mL of the starch solution.
- Titrate the released iodine with sodium thiosulfate 0.01 mol/L or 0.001 mol/L (depending on the expected oxidation level)
≈ 15 minutes / sampleMethod adapted from the NF EN ISO 3960 standard ("peroxide value") and the AOCS Official Method Cd 8-53