Oxidative stability of omega-3 and omega-6 oils: what formulators need to know

A high content of omega-3 or omega-6 fatty acids can make a plant-based oil nutritionally attractive. For formulators, however, it also presents an important technical challenge: how do you keep a sensitive oil stable throughout processing, storage, and the full shelf life of the finished product?

This is particularly relevant for oils rich in polyunsaturated fatty acids (PUFAs). These fatty acids are more susceptible to oxidation than saturated fatty acids. During oxidation, primary oxidation products such as hydroperoxides are formed first. As oxidation progresses, secondary products, including aldehydes, can develop and contribute to undesirable odours and flavours.

For product developers, this means that oil stability is not simply an inherent property of the raw material. The final stability depends on the interaction between the oil, processing conditions, antioxidants, packaging, and storage environment.

What happens during oxidation?

Oil oxidation can occur through several pathways. In autoxidation, lipids react with oxygen through a series of free-radical chain reactions. Light can also accelerate oxidation through photo-oxidation when certain photosensitising compounds are present. Temperature, oxygen availability, fatty acid composition, light exposure, and the presence of metals can all influence the process.

The early stages of oxidation are not necessarily immediately noticeable. Hydroperoxides can accumulate before significant sensory changes become apparent. They can subsequently break down into secondary oxidation products, some of which are responsible for rancid odours and flavours.

This is why relying on a single measurement or sensory assessment does not always provide a complete picture of oil stability.

Peroxide value and p-anisidine value

The peroxide value (PV) is widely used to assess primary oxidation products, particularly hydroperoxides. The p-anisidine value (p-AV) provides information about certain secondary oxidation products, particularly aldehydes.

For formulators, using these measurements together can provide a more complete picture of the oxidation status of an oil.

A low PV does not necessarily mean that an oil is free from oxidative deterioration. As hydroperoxides decompose, their concentration can change while secondary oxidation products continue to increase. For this reason, it is often useful to monitor oxidation using more than one relevant analytical parameter.

Why are omega-3 and omega-6 oils particularly challenging?

The susceptibility of an oil to oxidation is influenced, among other factors, by the degree of unsaturation of its fatty acids. Polyunsaturated fatty acids are generally more susceptible to oxidative reactions than less unsaturated fatty acids.

However, looking only at the omega-3 or omega-6 content is not enough.

Natural antioxidants, tocopherols, phenolic compounds and other minor components can influence stability. The way an oil has been extracted, refined, processed and stored can also make a difference.

This means that two oils with a similar fatty acid profile may behave differently during storage.

For formulators, this is an important consideration when assessing omega oil shelf life. The fatty acid profile tells only part of the story.

Camelina oil: an interesting example

Camelina oil is a good example of a plant-based oil where nutritional value and oxidative stability need to be considered together.

Camelina oil typically contains a substantial amount of alpha-linolenic acid (ALA), a polyunsaturated omega-3 fatty acid. Studies of different camelina oils have reported ALA levels around 35–40%, although the exact composition depends on factors such as cultivar, origin, growing conditions, and processing.

This makes camelina oil interesting for applications requiring a plant-based source of omega-3. At the same time, its fatty acid composition means that oxidative stability deserves careful consideration.

It is important, however, not to simply describe camelina oil as “highly unstable”. Research has shown that camelina oil can have considerable oxidative stability under certain conditions, partly due to its naturally occurring antioxidant components.

For example, research on cold-pressed Norwegian camelina oil found that the oil remained stable for 12 months under refrigerated storage at 4°C. Under storage at 20°C, oxidative changes were observed after approximately 6–9 months in centrifuged oil, while oil containing plant material showed greater stability under the conditions tested.

This illustrates an important point: the oxidative stability of an oil depends on the characteristics and processing of the specific raw material.

Natural antioxidants can make a difference

Plant-based oils naturally contain a range of minor components that can influence oxidative stability. Tocopherols are a well-known example. Other compounds, including certain phenolic components, can also contribute to the stability of an oil.

But here too, more is not necessarily better.

The effectiveness of an antioxidant depends on the type of antioxidant, its concentration, the oil composition, and the conditions under which the system is stored. Tocopherols, for example, can act as antioxidants but may also show pro-oxidant behaviour under certain conditions.

For formulators, the important question is therefore not simply:

Which antioxidant should we use?

It is:

Which antioxidant strategy performs effectively in this specific oil, formulation, and storage environment?

That is something that needs to be tested.

Oxygen, light, temperature and metals

When developing a stable oil-based product, several factors deserve attention.

Oxygen

Exposure to oxygen is one of the most important considerations. During processing, filling and storage, oxygen can come into contact with the oil. The amount of oxygen present in the headspace of a package can also be relevant.

Where technically feasible, reducing oxygen exposure can therefore contribute to improved stability.

Light

Light can accelerate photo-oxidation. Packaging is therefore not simply a marketing or design decision; it can directly influence the shelf life of a sensitive oil.

Depending on the application, opaque or light-protective packaging may provide an advantage over transparent packaging.

Temperature

Higher temperatures generally accelerate oxidative reactions. Accelerated stability tests make use of this principle, but results obtained at elevated temperatures should not automatically be converted into an exact shelf-life prediction under normal storage conditions.

They are particularly useful for comparing raw materials, formulations, antioxidant systems and packaging options.

Metals

Trace levels of metals such as iron and copper can promote oxidation. For sensitive oils, raw materials, processing equipment and contact materials should therefore be considered as part of the overall stability strategy.

Stabilising plant-based omega oils: look at the complete system

An effective approach to stabilising plant-based omega oils usually involves several complementary measures.

These may include:

• selecting a raw material with well-controlled oxidation parameters;

• minimising oxygen exposure during processing;

• controlling temperature and light exposure;

• managing trace metal contamination;

• developing an appropriate antioxidant strategy;

• selecting packaging with suitable oxygen and light protection;

• and defining storage conditions that reflect the intended distribution chain.

The appropriate combination depends on the application.

A liquid oil, softgel, emulsion and finished food product do not have the same physical or chemical environment. Consequently, they should not automatically be expected to have the same oxidative stability.

This is why applying one universal stabilisation strategy to every application can be problematic.

How should the shelf life of an omega oil be tested?

A good shelf-life strategy starts by identifying the quality parameters that are relevant to the specific product.

Depending on the application, these may include:

• peroxide value;

• p-anisidine value;

• calculated overall oxidation indicators, where appropriate;

• fatty acid composition;

• tocopherol content;

• sensory characteristics;

• and other product-specific quality parameters.

Accelerated oxidation tests can then be used to identify differences between raw materials, antioxidant strategies and packaging systems. Methods such as Rancimat and other accelerated oxidation tests can be useful for this purpose.

However, the results depend on the test method and conditions used. An accelerated test should therefore not automatically be interpreted as a direct prediction of real-world shelf life.

For commercial shelf-life claims, it is important to combine an appropriate analytical strategy with realistic storage conditions and testing of the actual finished product.

From raw material to finished product

One of the most important lessons when working with omega-rich oils is that raw material stability and finished-product stability are not the same thing.

An oil may remain stable under controlled conditions but behave differently once incorporated into a more complex formulation. Conversely, other ingredients within a formulation may have a protective effect.

Processing can also influence stability. Research on camelina oil, for example, has shown that the retention of certain plant-derived components can be associated with greater oxidative stability under the conditions studied.

This is why it is useful to assess not only the incoming oil but also the finished formulation.

A practical checklist for formulators

When developing a product containing plant-based omega-3 or omega-6 oils, the following checklist is a useful starting point.

Raw material

• What is the exact fatty acid profile?

• What are the oxidation values upon receipt?

• Which natural antioxidants are present?

• How was the oil extracted and processed?

• How was the oil stored before being incorporated into the product?

Processing

• Where does the oil come into contact with oxygen?

• What temperatures are reached during processing?

• Can contact with reactive metal surfaces be minimised?

• How long is the oil exposed to processing conditions?

Formulation

• Does oxidative stability change after incorporation into the finished product?

• Is additional antioxidant protection required?

• Are there relevant interactions with other ingredients?

Packaging

• How effectively does the packaging protect against oxygen?

• How much light reaches the product?

• Is headspace oxygen relevant?

• What storage conditions are realistic throughout the distribution chain?

Shelf life

• Which oxidation parameters should be monitored?

• Are the test conditions representative of the finished product?

• Are accelerated and real-time storage studies being used appropriately?

• Are analytical results supported by sensory evaluation where relevant?

Oxidative stability starts during product development

A good omega oil shelf life rarely results from a single ingredient or technical intervention.

It starts with the choice of raw material and continues through processing, antioxidant strategy, packaging, distribution and storage.

For formulators, this means that oxidative stability is best considered early in the development process—not only when a shelf-life test produces disappointing results.

This is particularly relevant for plant-based omega oils such as camelina oil. The same polyunsaturated fatty acids that make these oils nutritionally attractive also require careful management of oxidation.

The most reliable approach is therefore not to estimate shelf life from general rules of thumb, but to test the specific oil in the specific formulation under relevant storage conditions.

That provides a much stronger basis for shelf-life decisions—and gives formulators the information they need to make informed choices about raw materials, antioxidants, processing and packaging.