Peroxide Value of Edible Oils and Fats using Titration

Peroxide value gives the measure of rancidity in oils, fats and margarine. The number of R-OOH is determined using Iodometric titration. The amount of liberated iodine is titrated against sodium thiosulphate and is determined using combined platinum ring electrode. 

Fats and oils undergo changes during storage due to oxidation with air (Oxidative Rancidity). Oxidative rancidity in oils and fats is one of the major factors affecting the quality of these foods. Consuming rancid oil has an adverse effect on human health.  It can lead to cellular damage and also diseases like Diabetes, Alzheimer. Therefore it is very important to test these oils, fats and margarines for their purity with a precise, accurate and a convenient method. 

Based on the sample solubility, different solvents can be used such as acetic acid: chloroform, acetic acid: cyclohexane and acetic acid: isooctane in various proportions described in the application note.

The sample has to be protected from the air, stored in a cool, place and should not be opened before the determination is commenced. The samples will undergo oxidation with air (oxidative rancidity). Olive oil was analyzed after exposing to air and sunlight, the peroxide value found to be changed from 10.830 meq/kg to 14.640 meq/kg, hence support this statement.

Reaction:

- Generation of hydroperoxides: R-H + O₂ → R-OOH (Reaction I)

- Generation of iodine: KI + CH₃COOH → HI + CH₃COO-K+ (Reaction II)

                                     ROOH + 2HI → ROH + H₂O + I₂ (Reaction III)

- Titration step: I₂ + 2Na₂S₂O₃ → Na₂S₄O₆ + 2 NaI (Reaction IV)

The method is completely automated by using autotitrator along with titration autosampler.