What is a High Peroxide Value?
The peroxide value (PV) measures the amount of peroxides and hydroperoxides formed during the primary stage of oil oxidation. It is a key indicator of freshness and quality, with fresh oils having low PVs. When oil is exposed to heat, light, or oxygen, the unsaturated fatty acids begin to break down, forming these hydroperoxides. A high PV indicates that this process is well underway, leading to the oil's degradation and the potential formation of more harmful secondary oxidation products over time.
The Negative Effects on Oil Quality
A high peroxide value is a clear warning sign that the oil’s quality is severely compromised, affecting several key attributes. These effects are often noticeable and can impact the overall experience of using the oil.
Sensory Deterioration (Rancidity)
The most immediate and noticeable effect of a high peroxide value is the development of rancid off-flavors and odors. This happens as the unstable peroxides break down into a complex mix of volatile compounds, such as aldehydes and ketones, which are responsible for the characteristic unpleasant taste and smell of spoiled oil. This makes the oil unsuitable for cooking and spoils the food prepared with it.
Physical and Chemical Changes
Beyond sensory changes, a high PV causes significant physical and chemical alterations in the oil's composition:
- Increased Viscosity: Oxidized oils tend to become thicker and more viscous over time.
- Decreased Smoke Point: As oil oxidizes, its smoke point—the temperature at which it begins to produce smoke—decreases. This makes it more prone to burning during high-temperature cooking like frying, producing more toxic compounds.
- Nutrient Loss: The oxidation process targets and degrades essential nutrients present in the oil, particularly unsaturated fatty acids and antioxidants like Vitamin E.
- Polymer Formation: Repeated heating of oils with a high PV can lead to the formation of polymers, which manifest as gums and dark coloration in the oil.
Serious Health Implications
Consuming oils with a high peroxide value is not just a matter of poor quality; it can also have serious consequences for human health. The harmful compounds created during oxidation are known to be detrimental to the body.
Oxidative Stress and Inflammation
High peroxide levels and other oxidation products can increase free radicals in the body, leading to oxidative stress. This process can damage cells and tissues, contributing to chronic inflammation, which is a known precursor to many long-term health problems.
Links to Chronic Diseases
Research has linked the consumption of highly oxidized oils to a range of chronic illnesses:
- Cardiovascular Diseases: Oxidized lipids and trans fatty acids can contribute to inflammation and heart disease.
- Neurological Disorders: The detrimental effects of lipid oxidation have also been associated with neurological problems.
- Cancer: Some studies have connected the intake of highly oxidized oils to an increased risk of certain cancers.
- Diabetes and Liver Issues: Repeatedly heated cooking oils, which have high peroxide values, have been associated with type II diabetes and liver damage (hepatic steatosis).
Comparison of High vs. Low Peroxide Value Oil
| Feature | Low Peroxide Value Oil | High Peroxide Value Oil |
|---|---|---|
| Quality Indicator | Freshness and high quality | Deterioration and low quality |
| Sensory | Pleasant, characteristic taste and aroma | Rancid, sour, or unpleasant odor and flavor |
| Nutritional Content | Intact essential fatty acids and antioxidants | Degraded and depleted essential fatty acids and antioxidants |
| Smoke Point | High and stable | Low and decreasing |
| Health Risk | Safe for consumption | Potential health hazards due to toxic compounds |
| Storage Life | Longer shelf life | Significantly reduced shelf life |
How to Prevent a High Peroxide Value
Preventing high peroxide value is a matter of minimizing oil exposure to the factors that cause oxidation. By following these best practices, both consumers and food manufacturers can maintain oil quality and safety.
Best Practices for Storage and Handling
- Store in Cool, Dark Places: Heat and light are major catalysts for oxidation. Store oils in a cool, dark pantry or cabinet, away from the stove or direct sunlight.
- Use Opaque Containers: Use dark-colored glass or opaque containers to block out light exposure.
- Seal Tightly to Limit Air Exposure: Oxygen is a key reactant in the oxidation process. Always ensure the container is tightly sealed to minimize air contact. For bulk storage, using an inert gas like nitrogen in the headspace can be effective.
- Avoid Repeated Reheating: Repeatedly reusing oil, especially for deep frying, dramatically accelerates oxidation and increases the peroxide value. It is advisable not to reuse frying oil more than once.
The Role of Antioxidants
Antioxidants are substances that can delay or prevent the oxidation of fats and oils by neutralizing free radicals. Some oils naturally contain antioxidants, while others have them added during processing.
- Natural Antioxidants: Olive oil, for example, contains polyphenols, while some seed oils are rich in vitamin E, both of which are powerful antioxidants.
- Added Antioxidants: Synthetic antioxidants like BHA and BHT are often added to processed fats and oils to extend their shelf life and prevent rancidity.
Conclusion
In conclusion, understanding the effects of high peroxide value in oil is crucial for both food safety and health. It is a reliable measure of lipid oxidation and the resulting rancidity, which not only degrades the oil's quality but also creates potentially harmful compounds. From compromising sensory attributes to posing serious health risks like inflammation and chronic diseases, the consequences are significant. By adopting proper storage techniques, limiting exposure to heat, light, and air, and being mindful of the oil's freshness, both consumers and food producers can minimize these risks and ensure the quality and safety of their products. Monitoring the peroxide value is a simple yet powerful tool for quality control and should be considered a priority in oil manufacturing and handling.
References
- Oxidation of food grade oils - Oils, fats and more.
https://www.oilsfats.org.nz/documents/Oxidation%20101.pdf - Evaluation of the deleterious health effects of consumption of repeatedly heated palm oil in Wistar rats - NIH.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5616019/ - Peroxide Value Analysis of Fats and Oils - Measurlabs.
https://measurlabs.com/products/determination-of-peroxide-value/ - Edible Oil Quality - Oklahoma State University Extension.
https://extension.okstate.edu/fact-sheets/edible-oil-quality.html - INVESTIGATING CHANGES AND EFFECT OF PEROXIDE VALUE ON THE OIL QUALITY OF SELECTED EDIBLE OILS - fuuastjb.org.
https://fuuastjb.org/index.php/fuuastjb/article/download/106/101/191 - Rancidity in fats and oils: Considerations for analytical testing - EW Nutrition.
https://ew-nutrition.com/rancidity-fats-oils-considerations-analytical-testing/ - Awareness about the Hazards of Repeatedly Heated Cooking Oil - Journal of Bahria University Medical and Dental College.
https://jbumdc.bahria.edu.pk/download.php?id=277
