Determination of Acid Value and Peroxide Value are crucial in assessing the quality and stability of oils and fats.
Acid Value (AV)
– Measures the amount of free fatty acids (FFAs) present in an oil or fat.
– Calculated by titrating a sample with a strong base (e.g., KOH) to neutralize the FFAs.
– Expressed in mg KOH/g of sample.
– High AV indicates oil degradation, oxidation, or poor quality.
Preparation of the reagents:
Preparation 0.1 M sodium hydroxide: Dissolve 4.2 g of sodium hydroxide in sufficient carbon dioxide-free water to produce 1000 mL.
Preparation of Phenolphthalein solution: A 1.0% w/v solution of phenolphthalein in ethanol (96%).
The acid value IA is the number that expresses in milligrams the quantity of potassium hydroxide required to neutralize the free acids present in 1 g of the substance.
Dissolve 10.00 g of the substance to be examined, or the quantity prescribed (mg) in 50 ml of a mixture of equal volumes of alcohol R and ether R, previously neutralized with 0.1 M potassium hydroxide, unless otherwise specified, using 0.5 ml of phenolphthalein solution as indicator. When the substance to be examined has dissolved, titrate with 0.1 M potassium hydroxide until the pink color persists for at least 15 s
(End point (n)= ml of 0.1 M potassium hydroxide).
m= weight of the substance in g
Peroxide Value (PV)
– Measures the amount of peroxides present in an oil or fat, indicating oxidation level.
– Determined by reacting a sample with iodide ions, which release iodine proportional to the peroxide content.
– Expressed in meq/kg (milliequivalents per kilogram).
– High PV indicates oil oxidation, rancidity, or spoilage.
The peroxide value IP is the number that expresses in mill equivalents of active oxygen the quantity of peroxide contained in 1000 g of the substance as determined by the methods described below. When the monograph does not specify which method is to be used, method A should be applied. Any change from method A to method B should be validated.
- Preparation of the reagents:
- Starch Solution: Triturate 1.0 g of soluble starch with 5 mL of water and whilst stirring pour the mixture into 100 mL of boiling water containing 10 mg of mercuric iodide.
- 01 M sodium thiosulphate: Dissolve 2.5g sodium thiosulphate and 20mg of sodium carbonate in 1000ml water.
- Procedure:
- Place 3.00 g of the substance to be examined in a 250 ml conical flask fitted with a ground-glass stopper. Add 15 ml of a chloroform of 30 mL of glacial acetic acid. Shake to dissolve the substance and Add 1 mL of a freshly prepared solution of 1.3 g of potassium iodide in 1 mL of water.
- Shake for exactly 1 min and set aside in the dark for 3 minutes then add 100 ml of water R. Titrate with 0.01 M sodium thiosulphate adding the titrant slowly with continuous shaking until the yellow color is almost discharged. Add 5 ml of starch solution R and continue the titration, shaking vigorously, until the color is discharged (n1 ml of 0.01 M sodium thiosulphate).
- Carry out a blank test under the same conditions (n2 ml of 0.01 M sodium thiosulphate). The volume of 0.01 M sodium thiosulphate used in the blank titration must not exceed 0.1 ml.
Importance
1. Quality control: AV and PV help evaluate oil quality, stability, and shelf life.
2. Food safety: High AV and PV can indicate oil degradation, potentially leading to off-flavors, off-odors, or even toxicity.
3. Regulatory compliance: AV and PV are often specified in regulatory standards for oils and fats.
Factors Affecting AV and PV
1. Oxidation: Exposure to heat, light, oxygen, or metals can increase AV and PV.
2. Storage conditions: Poor storage conditions (e.g., high temperature, humidity) can lead to oil degradation.
3. Processing: Refining, bleaching, and deodorizing can impact AV and PV.
By monitoring AV and PV, manufacturers can ensure oil quality, stability, and safety.
Do you have specific questions about Acid Value, Peroxide Value, or oil quality analysis?
