ISO 18609:2000

Overview

ISO 18609:2000 specifies a laboratory method for determining the unsaponifiable matter content of animal and vegetable fats and oils using a three-stage hexane extraction. The method covers saponification with ethanolic potassium hydroxide, extraction of non-saponifiable components by hexane (or light petroleum), evaporation of solvent and gravimetric determination of the residue after drying. Note: the method is applicable to fats and oils but not to waxes, and it gives results that are systematically lower than the diethyl-ether method in ISO 3596.

Keywords: ISO 18609:2000, unsaponifiable matter, hexane extraction, animal and vegetable fats and oils, fat analysis, quality control

Key topics and technical requirements

• Scope: Determination of unsaponifiable matter in all fats and oils except waxes.
• Principle: Boil sample with ethanolic KOH to saponify; extract unsaponifiables with hexane; evaporate and weigh residue.
• Reagents: Analytical-grade n-hexane (or light petroleum 40–60 °C), ethanolic KOH (≈1 mol/L), ethanol wash solution, phenolphthalein indicator.
• Apparatus: 250 ml round-bottom flask with reflux condenser, 250 ml PTFE-stopcock separating funnels, boiling water bath, oven at 103 ± 2 °C (or vacuum drying).
• Procedure highlights:
  • Use ~5 g test portion; saponify 1 h under reflux.
  • Perform three successive 50 ml hexane extractions; combine extracts.
  • Wash extracts with ethanolic solution until neutral (phenolphthalein).
  • Evaporate solvent, dry residue at 103 °C and weigh to constant mass (repeat drying until mass change <1.5 mg).
  • Two determinations per sample and a reagent blank; blank residue must be ≤1.5 mg.
• Correction: Optional titration to correct for free fatty acids in the residue (using 0.1 mol/L ethanolic KOH) is specified.
• Precision: Collaborative study results show mean unsaponifiable contents 0.15–0.58% (m/m). Repeatability limits ≈0.06% and reproducibility limits ≈0.18% (values vary with matrix).

Applications and users

ISO 18609:2000 is relevant for:

• Quality control and laboratory analysis in edible oil processing and refining
• Food industry laboratories monitoring oil purity and compositional parameters
• Analytical labs performing comparative methods for regulatory or specification testing
• Research groups studying sterols, hydrocarbons and other non-saponifiable lipid fractions

This method supports routine gravimetric analysis of unsaponifiable fractions where hexane extraction is preferred or specified.

Related standards

• ISO 3596 - Unsaponifiable matter by diethyl ether extraction (reference method; produces higher results).
• ISO 661 - Preparation of test sample for fats and oils (normative reference).
• ISO 5555 - Sampling of animal and vegetable fats and oils (recommended sampling practice).

For implementation, laboratories should follow ISO 18609:2000 procedural details and report results with full method and sampling information as specified in the standard.