Fat oxidation is one of the reasons why food products can lose their characteristic flavour and aroma before the end of their declared shelf life. The problem is that these changes are not always immediately noticeable through sensory evaluation. By the time a rancid smell becomes apparent, the oxidation process has generally progressed considerably, leaving fewer options for preserving product quality.
For food manufacturers, identifying the early indicators of oxidation is therefore more important than reacting only after a customer complaint occurs.
Peroxide Value Alone Is Not Enough to Assess Stability
Peroxide value is one of the main parameters used to assess the oxidation status of oils and fats. It indicates the amount of primary oxidation products, namely peroxides and hydroperoxides, formed during the initial stages of the process.
However, there is an important point to consider. Peroxides gradually break down, producing secondary oxidation products, including aldehydes responsible for characteristic off-odours and flavours. As a result, a low peroxide value does not necessarily mean that an oil is fresh or has good oxidative stability.
When a more detailed assessment is required, the anisidine value can also be considered, as it provides additional information about certain secondary oxidation products. Evaluating both parameters together provides a more complete picture than relying on a single result.
Why Can the Problem Appear Only in the Finished Product?
The quality of the oil at the time of delivery is not the only factor determining the stability of the finished product. The rate of oxidation is also influenced by fatty acid composition, exposure to oxygen and light, temperature, the presence of trace metals and packaging characteristics.
For example, a product containing unsaturated fats may be particularly susceptible to oxidation during storage. In biscuits, filled wafers and confectionery creams, the process can develop gradually. The product may have the expected flavour immediately after production, while undesirable aromas emerge only after a certain period.
Packaging deserves particular attention. Even when it provides effective moisture protection, it may not necessarily offer a sufficient barrier against oxygen. Packaging selection should therefore be considered alongside the characteristics of the fat phase and the intended shelf life.
Oil Selection Affects Shelf Life, Not Just Cost
Different oils do not have the same oxidative stability. One of the reasons is their fatty acid composition. Under comparable conditions, oils with a higher proportion of polyunsaturated fatty acids are generally more susceptible to oxidation than oils with a higher proportion of monounsaturated fatty acids.
For this reason, high-oleic varieties of vegetable oils are considered in certain applications where improved oxidative stability is desirable. However, these oils are not immune to oxidation. The outcome depends on the overall formulation, processing methods, storage conditions and protection against oxygen.
Antioxidants should not be regarded as a universal solution either. Their effectiveness depends on the type of fat, concentration, product composition and conditions of use. When properly selected and applied, they can slow oxidation, but they cannot restore the quality of fat that has already undergone significant oxidative deterioration.
What Should Be Checked Before Rancid Flavours Develop?
Assessing oxidative stability should start with the raw material specification and the analytical results for the specific batch. Depending on the type of oil and its intended application, it may be useful to review the peroxide value and, where appropriate, the anisidine value, together with the recommended storage conditions and shelf life.
For products with longer shelf lives, monitoring changes over time is particularly important. Testing only at the beginning does not provide a complete picture of how the product will perform during storage. Stability studies conducted under appropriate conditions can help determine whether the existing formulation, packaging and storage conditions are sufficient to maintain the expected sensory quality.
A reliable assessment therefore does not depend on a single parameter or simply on the choice of oil. The best results are achieved when raw material quality, laboratory analysis, formulation and storage conditions are considered as parts of the same system.