How to Use EPR Technology to Evaluate Edible Oil Quality

July 18, 2024

From rich peanut oil to fragrant olive oil, edible vegetable oils enrich our diets and provide diverse nutritional benefits. With rising living standards and increasing oil consumption, ensuring the quality and safety of edible oils has become critical.

Why EPR Is a Powerful Tool to Evaluate Edible Oil Quality

Using Electron Paramagnetic Resonance (EPR) to Evaluate Oil Quality

EPR technology offers unique advantages: no sample pretreatment, non‑destructive, in‑situ, and highly sensitive. It is increasingly used in edible oil quality monitoring.

EPR can detect unpaired electrons in oil molecules, which are early markers of oxidation.
Oil oxidation is essentially a free radical chain reaction, producing radicals such as ROO·, RO·, and R·.
By identifying these radicals, EPR allows scientific evaluation of oxidation level and stability before visible or sensory changes appear.

This early detection is critical for preventing degradation caused by light, heat, oxygen exposure, or metal catalysts. Unsaturated fatty acids are particularly prone to oxidation, even at room temperature, which affects flavor, nutrition, and shelf life.

Benefits of using EPR for oil stability:

Ensures safer, fresher edible oil for consumers.
Guides effective antioxidant use.
Supports quality control in oil‑containing foods.
Extends product shelf life.

Thus, EPR technology provides a direct, sensitive, and non‑destructive approach to monitor edible oil quality, safeguarding public health.

Practical Applications of EPR in Oil Monitoring

Principle

During lipid oxidation, various free radicals are generated.
These radicals are highly reactive and short-lived, so spin trapping is often used.
Spin trapping agents (like PBN) react with unstable radicals to form stable radical adducts that EPR can detect reliably.

Application 1: Evaluating Oxidative Stability

During each step of production, the free radical concentration can be measured, and the gradual changes in oxidation can be tracked. This allows for a precise determination of the product’s antioxidant capacity.

For example, when PBN is used to trap radicals generated during peanut oil oxidation, stable radical adducts form. The EPR spectra of these adducts provide direct insight into oil oxidation. The stronger the EPR signal, the higher the free radical content, and the more oxidized the oil is.

EPR spectra also reveal the effects of external factors, such as temperature. As temperature increases, the EPR signal intensity of radicals rises, indicating that higher temperatures accelerate oil oxidation.

Evaluate the Quality of Edible Oil

Evaluating Oxidative Stability

Application 2: Assessing Antioxidant Effectiveness

This study compares the effects of different antioxidants on the EPR signal intensity of peanut oil. Various antioxidants were added to the oil, including VE, BHT, BHA, a combination of BHA + BHT, and a combination of TBHQ + CA. As shown in the Figure, the Y-axis represents the spin concentration. Samples with added antioxidants show significantly lower spin signals compared to the control (peanut oil control, black line). This indicates that antioxidants effectively reduce free radical formation during oil oxidation.

The contribution of each antioxidant to oil stability differs. The observed order of effectiveness is: TBHQ + CA > BHA + BHT > BHA > BHT > VE. Notably, the combination of BHA + BHT performs better than either BHA or BHT alone. The combination of TBHQ + CA shows the best antioxidant effect

This enhanced effect is partly due to metal ions, especially Cu²⁺ and Fe²⁺, which can catalyze oil oxidation. CA acts as a chelating agent, binding metal ions and further preventing oxidative reactions.

Application 3: Oil Quality Monitoring – Detecting Adulteration

"Gutter oil" refers to recycled restaurant oil, often degraded by repeated heating. EPR can detect high levels of free radicals, assessing quality and safety.

The method is straightforward:

Use refined plant oil as raw material and add PBN spin trap.
Measure radical intensity before and after adulteration.
Apply spectral fitting to build a standard curve linking radical intensity to adulteration ratio.

This approach is highly sensitive and easy to operate. It can accurately quantify adulteration below 20%, providing a reliable tool for quality control.

Application cases of EPR in oil monitoring

Reference: A method for identifying gutter oil in refined vegetable oil, 201610515761.X

CIQTEK EPR Spectrometers

Provides non-destructive, direct detection of paramagnetic species.
Rapidly and accurately determines antioxidant capacity and monitors oil oxidation.
Detects radicals in oils, as well as paramagnetic molecules, rare earth ions, ion clusters, doped materials, defects, and metalloproteins.
Applications extend to chemistry, biology, physics, medicine, food, and industry.

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