Overview
EN ISO 3656:2011 - "Animal and vegetable fats and oils - Determination of ultraviolet absorbance expressed as specific UV extinction" specifies a spectrophotometric method for measuring ultraviolet (UV) absorbance of fats and oils. The standard defines how to determine specific UV extinction (K values) for animal and vegetable oils using diluted solutions in either isooctane or cyclohexane, with measurements made in a 10 mm quartz cell. Results are used as quality, purity and authenticity criteria (e.g., to indicate refining or oxidation).
Key topics and technical requirements
- Scope: Measurement of UV absorbance of animal and vegetable fats and oils to calculate specific extinction coefficients (K232, K268, K270).
- Solvents & wavelengths:
- Isooctane: measure at 232 nm and 268 nm.
- Cyclohexane: measure at 232 nm and 270 nm.
- Solvent UV purity: absorbance < 0.12 at 232 nm and < 0.05 at 250 nm.
- Test concentration and cell: typical solution concentration is 1 g per 100 ml; pathlength = 10 mm (1 cm). The specific extinction Kλ = Eλ / (c · s) where Eλ is measured extinction, c is concentration (g/100 ml), s is pathlength (cm).
- Apparatus & calibration:
- UV spectrometer with quartz 10 mm cells.
- Wavelength accuracy checked with holmium oxide filter; photometric accuracy checked with potassium dichromate reference cells.
- Clean glassware, class A 25 ml volumetric flasks, analytical balance (readability to 0.0001 g).
- Sample preparation: Follow ISO 661 for test sample prep; ensure homogeneity, filter if turbid; methods for liquid oils and hard fats are specified.
- Procedure: Dissolve weighed test portion to achieve absorbance ~0.2–0.8, record absorbance 220–360 nm (or selected intervals around maxima). Dilute if absorbance > 0.8.
- Results & precision: Report K values to two decimal places. The standard includes interlaboratory precision data and defines repeatability/reproducibility concepts.
Applications and users
- Quality control laboratories in edible oil and animal fat processing.
- Olive oil industry for detecting refining or adulteration (ΔK and K values are used in authenticity testing).
- Regulatory authorities and testing bodies referencing oil standards.
- R&D and analytical service providers assessing oxidation, refining effects, and shelf-life indicators.
- Typical uses: monitoring refining, detecting oxidation products (conjugated dienes/trienes and α,β‑unsaturated carbonyls), verifying product labeling and import/export quality checks.
Related standards
- ISO 661 - Preparation of test sample (referenced)
- ISO 5555 - Sampling of fats and oils (recommended sampling)
- Commission Regulation (EEC) No 2568/91 - olive oil spectrophotometric criteria (referenced)
- IOC / national methods for olive oil UV absorbance
Keywords: EN ISO 3656:2011, ultraviolet absorbance, specific UV extinction, K232, K268, K270, isooctane, cyclohexane, spectrophotometric method, animal and vegetable fats and oils.
