K232 and K270: What UV Extinction Coefficients Measure in Olive Oil

1What are UV extinction coefficients?

The UV extinction coefficients (known as K-values) are spectrophotometric parameters that measure how much ultraviolet light the oil absorbs at specific wavelengths. This absorption is directly linked to structural alterations in the fatty acids caused by oxidation or heat treatments.

They are measured quickly using a UV spectrophotometer, without destroying the oil sample.

2K232: Primary Oxidation

At 232 nm, the spectrophotometer measures conjugated dienes—compounds formed when the double bonds of polyunsaturated fatty acids rearrange due to free radical attacks. * What it measures: The early, primary stages of oxidation. * Legal limit for Extra Virgin: K232 ≤ 2.50 * A fresh, premium-quality oil usually scores between 1.50 and 2.00.

3K270: Secondary Oxidation

At 270 nm, the instrument measures conjugated trienes and carbonyl compounds (aldehydes, ketones). These are secondary oxidation products formed when primary hydroperoxides break down. * What it measures: Advanced, secondary oxidation. It indicates that the oil is old, rancid, or has undergone industrial refining. * Legal limit for Extra Virgin: K270 ≤ 0.22 * An excellent, fresh oil usually scores between 0.08 and 0.14.

4Delta-K (ΔK): The purity safeguard

The Delta-K (ΔK) value is a calculation that measures the curvature of the UV absorption spectrum around 270 nm:

ΔK = K270 − (K266 + K274) / 2

A high ΔK value is a clear indicator that the oil has been blended with refined olive oils (which have very high triene counts due to high-temperature deodorization). * Legal limit: ΔK ≤ 0.01

5Understanding K-Values at a glance

| Quality Tier | K232 | K270 | | :--- | :--- | :--- | | Fresh Artisanal Oil | 1.50–2.00 | 0.08–0.14 | | Good Quality | 2.00–2.40 | 0.14–0.20 | | Standard EVOO | 2.40–2.50 | 0.20–0.22 | | Defective (Not EVOO) | > 2.50 | > 0.22 |