The peroxide value is a key parameter for determining the oxidation level of fats, such as vegetable oils, animal fats, and resins. This indicator assesses the quality and stability of fats based on their active oxygen content. In many sectors, including food , cosmetics, and pharmaceuticals, this value is commonly used to monitor freshness and prevent rancidity in products containing unsaturated fats.
This article explores in detail the meaning of the peroxide value, measurement methods, factors influencing its value, and applications in various industrial sectors.
1. Definition of the peroxide value
1.1 What is the peroxide value?
The peroxide value measures the amount of active oxygen, primarily in the form of peroxides and hydroperoxides, present in fats and oils. Peroxides are formed during the oxidation of unsaturated fatty acids, a natural process that leads to the degradation of fats. This value is particularly important for assessing the quality of oils and fats intended for human consumption or cosmetic applications, as a high peroxide value indicates an advanced level of oxidation.
1.2 Importance of the peroxide value in industry
The peroxide value is crucial for several reasons:
- Product freshness assessment : A low index suggests fat that is still fresh, while a high index signals advanced degradation.
- Quality assurance : Producers can use this index to verify that their products meet quality standards.
- Prevention of health risks : A high peroxide value in a cooking oil may indicate the presence of potentially toxic compounds, including aldehydes.
In summary, this index helps to guarantee the quality and safety of fatty products, while preserving their taste and sensory characteristics.
1.3 Other complementary indicators for the evaluation of fats
In addition to the peroxide value, other important parameters characterize the quality of fats and oils, such as the anisidine value, which measures the non-volatile aldehyde compounds formed during subsequent oxidation stages. Another frequently measured parameter is the saponification value . This value reflects the amount of alkali required to transform a fat or oil into soap and indirectly indicates the average size of the fatty acid chains. Combined with the peroxide value, the saponification value provides a more comprehensive assessment of the stability and quality of fats and oils.
2. Oxidation process of fats and oils
2.1 Oxidation and peroxide formation
Fat oxidation begins with the interaction between oxygen and unsaturated fatty acids. This process forms peroxides, and several factors accelerate this reaction:
- Exposure to oxygen and light : The more a fat is exposed to air and light, the more vulnerable it is to oxidation.
- High temperature : Heat accelerates oxidation, especially during processes like frying.
- Catalytic metals : The presence of metals such as manganese and iron in storage containers can catalyze oxidation.
The peroxides then transform into secondary compounds, including aldehydes, which give oils and fats a rancid taste and smell.
2.2 Implications of rancidity
Rancidity is the advanced stage of fat oxidation. It not only alters the sensory qualities (taste, smell) of food, but it can also render fats unfit for consumption. The resulting compounds, such as aldehydes, can have toxic effects. Therefore, the peroxide value allows for the detection of the first signs of rancidity, even before unpleasant odors appear.
3. Why measure the peroxide value?
3.1 Quality Control
Measuring the peroxide value is an integral part of quality control in the fats and oils industry. It helps verify that oils and fats meet quality standards before being placed on the market. For example, the WHO recommends that a cooking oil have a peroxide value below 26 to be considered safe for consumption.
3.2 Prevention of toxicity risks
Beyond a certain threshold, peroxides and secondary compounds become dangerous to human health. This is why regulations impose strict limits, especially for food products. The WHO sets the acceptable limit at 26 meq of active oxygen per kilogram of oil, beyond which health risks increase.
3.3 Practical applications in the choice of packaging and preservatives
Preservation methods, such as the addition of natural antioxidants (essential oils), and the choice of packaging materials (e.g., tinted glass bottles) help to reduce the rate of fat oxidation.
4. Methods for measuring the peroxide value in the laboratory
4.1 Iodometric titration: Wheeler method
The Wheeler method, standardized by international organizations, involves using potassium iodide in an acidic medium. This method is based on a chemical reaction where peroxides oxidize potassium iodide, releasing iodine. The amount of iodine released is then measured, allowing the peroxide value to be calculated.
4.2 Potentiometric Method
The potentiometric method detects the stagnation point by measuring changes in electrical potential. Although less common, this technique is accurate and useful for samples with low water content.
4.3 Importance of standards and precautions to take
The standards (ISO 3960 and NF EN ISO 27107) define the assay protocols. They also specify the sample quantities to be used to guarantee accurate and reproducible results. Incorrect sample preparation or variations in mass can skew the results, hence the importance of strictly following the protocols.
Are you looking for an analysis?
5. Understanding TotOx: Measurement of total oxidation
5.1 What is TotOx?
The TotOx (or total oxidation) is an indicator that combines the peroxide value and the anisidine value, providing a more comprehensive measure of the oxidation state of fats. Its calculation is simple: TotOx = (2 x peroxide value) + anisidine value .
5.2 Advantages of using TotOx to assess the degradation state of oils
Unlike the peroxide value alone, TotOx takes into account secondary compounds formed during oxidation, thus providing a more complete assessment of oil degradation.
5.3 Interpretation of TotOx values in edible oils
As a general rule:
- TotOx < 10 : good quality oil.
- TotOx < 26 : acceptable oil.
- TotOx > 26 : oil too oxidized, not recommended for consumption.
6. Causes and factors influencing high peroxide values
6.1 Environmental and Storage Factors
The oxidation rate of fats increases with exposure to air, light, and heat. To prevent this, oils should be stored in airtight containers, away from light, and at low temperatures.
6.2 Presence of catalytic metals
Metals such as iron and manganese accelerate oxidation. Manufacturers take care to use containers free of reactive metals to limit this reaction.
6.3 Storage duration and conditions
High-quality oils are more prone to oxidation if stored for a long time, particularly under unsuitable conditions.
7. Limits and critical thresholds of the peroxide value
7.1 Peroxide value and risk of rancidity
For a quality oil, the peroxide value should be less than 5 meq/kg. Above this level, the risk of rancidity increases, making the oil less flavorful and potentially harmful.
7.2 Indicators of toxicity for human consumption
Peroxide value levels are regulated by international health agencies, which establish thresholds to prevent any risk of toxicity. A peroxide value above 26 is considered unfit for consumption.
8. Applications of the peroxide value in different sectors
8.1 Food sector
Cooking oils and fats must have a low peroxide value to ensure product safety and quality. Regular monitoring is necessary to guarantee compliance.
8.2 Cosmetics sector
In cosmetics , the peroxide value is used to assess the stability of oily ingredients. A value that is too high indicates product deterioration, which can be harmful to the skin.
8.3 Pharmaceutical and food supplement sector
Products rich in polyunsaturated fatty acids, such as omega-3s, are susceptible to oxidation. Manufacturers must monitor the peroxide value to ensure the efficacy and safety of dietary supplements.
Conclusion
The peroxide value remains an essential tool for ensuring the quality and safety of fats and oils in many sectors. Faced with increasing demand for high-quality products, measurement methods and standards are constantly evolving to meet consumer needs.
