Overview
ISO 11702:2016 specifies an enzymatic staining test for the quantitative determination of total sterols in animal and vegetable fats and oils, fatty foods and related products. The method measures both free and esterified sterols on sample quantities of 1 g to 2 g of fat. Results are reported as cholesterol for animal fats and β‑sitosterol for vegetable fats. The procedure is spectrophotometric and based on oxidation of 3‑hydroxysterols by cholesterol oxidase and formation of a coloured lutidine dye measured at 405 nm.
Note: ISO 11702:2016 is not applicable to dark‑coloured fats and oils, milk and milk products (or fat derived from them), nor has it been validated for products fortified with high levels of added sterols. The enzyme oxidizes several 3‑hydroxysterols and is therefore not cholesterol‑specific.
Key topics and requirements
- Principle: saponification → isolation of unsaponifiable fraction → enzymatic oxidation (cholesterol oxidase) → dye formation (acetylacetone/formaldehyde chemistry) → spectrophotometric measurement at 405 nm.
- Sample size: 1–2 g of fat; ensure final test solution sterol concentration is within method range.
- Quantification: dye absorbance converted to sterol mass concentration and expressed as mg sterols per 100 g of fat (cholesterol basis for animal, β‑sitosterol basis for vegetable).
- Reagents and apparatus: specified enzyme preparations (cholesterol oxidase, catalase), methanolic KOH for saponification, buffer systems, and a spectrophotometer with 1 cm cuvette.
- Limitations: not suitable for dark coloured matrices or milk fats; enzyme reacts with other 3β‑hydroxysterols; not validated for sterol‑fortified products.
- Performance: includes interlaboratory precision data and definitions for repeatability and reproducibility limits.
Practical applications
- Quality control and compositional analysis in edible oils and fats manufacturing.
- Routine testing in food testing laboratories for sterol profiling of vegetable and animal fat products.
- Regulatory and labeling compliance where total sterol content is required.
- Research applications measuring total phytosterols in plant oils (expressed as β‑sitosterol).
Who uses ISO 11702:2016
- Food and oil industry laboratories (QC/QA teams)
- Third‑party testing and certification bodies
- Regulatory laboratories and inspectors
- Academic and industrial researchers analyzing sterol content in fats and oils
Related standards
- ISO 661 - Preparation of test sample (referenced for sample prep)
- ISO 3696 - Water for analytical laboratory use
- ISO 5555 - Recommended sampling (sampling not part of ISO 11702)
- Method equivalence noted to IUPAC method 2.404 and DGF F‑III 2 (91)
Keywords: ISO 11702:2016, sterols, enzymatic determination, animal and vegetable fats and oils, cholesterol oxidase, spectrophotometric assay, total sterol content.
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