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Food, feed and beverage · EPR

Oxidative stability and antioxidants

Oxidation starts with radicals, long before a product smells or tastes off. EPR detects these radicals directly, so it shows how well an oil, a beer or a wine resists oxidation and how effective an antioxidant is, before the shelf life has run out.

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What it tells you

The earliest sign of ageing

Fats, oils, beverages and many foods age through chains of reactions in which radicals are formed. Taste and smell change only later, when the damage is done. EPR (electron paramagnetic resonance) is the technique that sees radicals themselves.

A well-protected product keeps radicals away for a long time under stress, and a poorly protected one does not. The time before radicals start to build up, the lag time, is a measure of its stability. The same approach rates the effect of an antioxidant, a recipe change, a packaging choice or a storage condition.

Typical samples

Where it is used

  • Edible oils and fats
  • Beer, where flavour stability is a central quality criterion
  • Wine and other beverages
  • Emulsions such as mayonnaise and dressings
  • Plant extracts and ingredients with antioxidant claims

Typical tasks are predicting shelf life, comparing recipes, ingredients, packaging or process steps, ranking antioxidants, and screening raw materials.

How it works

Catching radicals so they can be counted

Radicals in a product live only for a moment, far too briefly to be measured. A spin trap is added to the sample. It reacts with the radicals and forms a stable compound that lives long enough to be measured. The height of the EPR signal is the amount of radicals trapped, and the pattern of lines identifies the kind of radical.

A short-lived radical is caught by a spin trap, forming a stable adduct that gives an EPR spectrum
The principle of spin trapping. Schematic illustration.

To avoid waiting for months, the sample is aged under controlled stress, for example at a raised temperature, and measured at regular intervals. The result is a curve of radical signal against time, and the lag time is read from it.

Radical signal against time under forced ageing: a well protected product shows a long lag before radicals appear, a poorly protected one a short lag
Lag time before radicals build up. Schematic illustration, not measured data.
Why EPR

What it adds

  • Sees the radicals themselves, not only the products of oxidation that appear later
  • Responds before taste, smell or colour change
  • Works on coloured and turbid products such as beer, wine and oils
  • A small sample is enough
  • Forced ageing shortens the wait compared with real-time storage tests
  • Benchtop instruments make the technique practical in a quality laboratory
Good to know

Points that matter in practice

  • The stress conditions should resemble real storage, so they are chosen and checked for each product
  • The spin trap and the conditions are matched to the type of product, and results are compared only within the same method
  • The link between the lag time and the real shelf life, or a sensory panel, should be established for your own product
  • Conventional oxidation tests are widely used. Check how the results of the two methods relate for your product before replacing one with the other
  • EPR detects unpaired electrons only. It does not replace tests for other aspects of quality
How MSY Consulting helps

From your product to a routine method

Send or bring representative samples. MSY Consulting runs feasibility measurements on your product, defines the stress conditions and the spin trap with you, helps you relate the results to shelf life or sensory tests, and trains your team until the measurement is part of your routine.

Other markets
Contact

Let's talk about your application

Send an email describing your instrument and your application, and you will get a reply.

contact@msyconsulting.eu

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