Why do peroxide values increase in oils?
When assessing the quality of vegetable oils, the peroxide value is a parameter that often raises questions. Particularly in seed and fruit oils, elevated values can occur. However, a high peroxide value alone does not automatically indicate reduced oil quality.
Seed and fruit oils often contain high levels of polyunsaturated fatty acids. These fatty acids are particularly sensitive to oxygen and can therefore be more susceptible to oxidation.
Even within the raw material, small amounts of primary oxidation products can form during ripening, harvesting and processing. The fine distribution of oil within seed or fruit tissues creates a large surface area where contact with oxygen can occur, potentially promoting oxidative processes. These early oxidation products are reflected in the peroxide value.
Correctly interpreting elevated peroxide values in native oils
Especially in native and cold-pressed oils, natural components and oxidation products are not removed through refining steps. As a result, peroxide values can vary depending on the raw material, initial quality and processing conditions.
An elevated peroxide value is therefore not automatically an indication of inferior oil quality. For a reliable quality assessment, this value must always be considered together with additional analytical parameters and sensory characteristics.
A holistic assessment instead of a single value
The peroxide value indicates the presence of primary oxidation products. Therefore, it should be evaluated together with other quality parameters – particularly the acid value and sensory properties.
A low acid value indicates a low level of hydrolytic degradation of the oil. A fresh, characteristic aroma and an unremarkable sensory profile can indicate that, despite measurable primary oxidation products, no advanced quality deterioration has occurred.
It should also be considered that primary oxidation products can further break down into secondary oxidation products, which are often more responsible for typical ageing characteristics and off-flavours.
Conclusion
The peroxide value is an important parameter for evaluating oil quality, but it should never be considered in isolation. Particularly in high-quality native seed and fruit oils, elevated peroxide values can have natural causes and must be interpreted within the context of the overall quality profile.
Only the combination of analytical parameters and sensory evaluation enables a reliable assessment of an oil’s condition, freshness and quality.