ISO 16931:2009

Overview

ISO 16931:2009 specifies a standardized laboratory method for the determination of polymerized triacylglycerols (PTAGs) in animal and vegetable fats and oils using high-performance size-exclusion chromatography (HPSEC). PTAGs (dimeric and oligomeric triacylglycerols) form during heating and frying; measuring PTAGs is a direct way to assess the thermal deterioration of frying fats. The method applies when PTAGs are at least 3% mass fraction (from peak areas) and can also be applied to fats used in animal feed (with caution regarding extraction effects).

Key topics and technical requirements

• Analytical technique: HPSEC (gel permeation chromatography) with a refractive index (RI) detector.
• Sample preparation: Follow ISO 661 for test-sample preparation; dissolve ~100–300 mg sample in 10 mL tetrahydrofuran (THF), homogenize and filter (0.45 µm nylon) if needed.
• Eluent and reagents: THF (HPLC grade, degassed, water content matched to eluent); toluene also referenced for column storage/changeover; BHT stabilization may be used.
• Columns and conditions: Two columns in series (recommended 2 × 300 mm, styrene–divinylbenzene packing, 5 µm), column temperature controlled at 30–35 °C, typical flow 0.5–1.0 mL/min (example: 0.8 mL/min), injection 20–40 µL.
• Detection and quantification: RI detection with matched detector temperature; internal normalization is used assuming equal response coefficients for eluted components. Calculation: w_PTAGS = (sum of PTAG peak areas / sum of all acylglycerol peak areas) × 100. Report to one decimal place.
• Quality and precision: Annex B provides interlaboratory precision data (repeatability and reproducibility). A guard column is recommended and column efficiency should be ≥ 6 000 theoretical plates for TAGs.
• Safety: THF is hazardous-follow applicable handling and safety regulations.

Applications and users

ISO 16931:2009 is used for:

• Food quality control - monitoring frying oil degradation in restaurants and food processors.
• Analytical laboratories - routine testing of oils and fats for PTAG content by HPLC/HPSEC.
• Oil and fat manufacturers - product quality assessment and shelf-life studies.
• Regulatory and research institutions - standard method for comparative studies and compliance.
• Animal feed testing - determination of polymer content in feed fats (note: extraction method affects results).

Keywords: ISO 16931:2009, HPSEC, polymerized triacylglycerols, PTAGs, frying fats, thermal deterioration, HPLC, refractive index detector.

Related standards

• ISO 661 - Preparation of test sample (fats and oils)
• ISO 5555 - Sampling (recommended)
• ISO 5725 series - Precision (repeatability and reproducibility)
• ISO 6492 - Animal feeding stuffs - Determination of fat content
• IUPAC Method 2.508 - Determination of polymerized triglycerides by HPLC