Overview
ISO 1740:2004 (IDF 6:2004) specifies a reference method for determining the fat acidity of milkfat products and butter. Fat acidity is reported as millimoles of free fatty acids per 100 g of fat and quantifies the amount of alkali needed to neutralize free fatty acids in a test portion. This International Standard defines reagents, apparatus, sampling notes, stepwise laboratory procedure (including preparation, titration, blank and check tests), result calculation and precision limits.
Key topics and technical requirements
- Scope: Applies to milkfat products (anhydrous milkfat, butter oil, ghee) and butter; butter requires fat separation by centrifuging before analysis.
- Principle: Melt/filter fat, dissolve in a solvent mixture, then titrate with a standard tetra-n-butylammonium hydroxide solution using thymol blue as indicator.
- Reagents
- Tetra-n-butylammonium hydroxide standard solution, nominally 0.10 mol/L in propan-2-ol/methanol (3:1).
- Thymol blue indicator in propan-2-ol and a fat solvent (thymol blue solution mixed with light petroleum 60–80 °C boiling range).
- Titrant concentration must be checked by titration against potassium hydrogen phthalate (KHP) before use.
- Apparatus essentials
- Analytical balance (0.01 g), centrifuge (≥350 g) for butter, oven maintained at 50 °C ± 2 °C, burette graduated to 0.02 ml, nitrogen supply free of CO2.
- Procedure highlights
- Melt and filter fat at 50 °C; weigh 5–10 g test portions.
- Dissolve fat in fat solvent (50 ml), titrate under nitrogen to exclude CO2 until a persistent color change (yellow to faint greenish) is observed.
- Perform blank and check tests (using prepared reference fat spiked with known palmitic acid) each series; neutralize solvent if blank is high.
- Expression of results: Calculate fat acidity in mmol/100 g fat to two decimal places; alternative conversions to acid value (mg KOH/g) and % oleic acid are provided.
- Precision: For fat acidity in the range 0.20–2.00 mmol/100 g, repeatability requires that two tests differ by ≤ 0.05 mmol/100 g in 95% of cases.
Applications and users
- Quality control and laboratory analysts in the dairy industry (butter and milkfat producers).
- Regulatory and food safety laboratories verifying product freshness and lipid degradation.
- Research laboratories studying lipid hydrolysis, shelf-life, processing effects or formulation.
- Relevant for product specification, incoming raw material testing, process control and compliance with international dairy standards.
Related standards
- ISO 707 - recommended sampling method for milk and milk products.
- ISO 2446 - reference to Gerber-type centrifuges and centrifugation practice.
- ISO 5725 - methods for determining repeatability and reproducibility of measurements.
Keywords: ISO 1740:2004, fat acidity, milkfat products, butter, reference method, titration, tetra-n-butylammonium hydroxide, thymol blue, dairy quality control.
