🍎 Acidity of fats (acid value)
In short
Determination of acid value and acidity in edible fats and oils by alkalimetric titration. The test is performed according to PN-EN ISO 660:2020; Range: 0.05–200 mg KOH/g. The procedure comprises 5 steps (about 18 min in total); it is used for: Quality control of vegetable oils (rapeseed, sunflower, olive), Analysis of animal fats (lard, butter), Monitoring fat rancidity during storage.
At a glance
- Standard: PN-EN ISO 660:2020
- Category: Food Chemistry
- Procedure steps: 5
- Total time of stages: 18 min
- Result: Acid value [mg KOH/g] or % oleic acid
- Range: 0.05–200 mg KOH/g
- Limit (extra virgin olive oil): ≤0.8% oleic acid
Overview
Acid value (AV) defines the amount of mg KOH needed to neutralize free fatty acids in 1 g of fat. Acidity is also expressed as % oleic acid. This parameter is an indicator of fat quality and freshness — increasing AV indicates triacylglycerol hydrolysis (hydrolytic rancidity).
The method involves dissolving the fat sample in a solvent mixture (ethanol/diethyl ether) and titrating free fatty acids with KOH solution using phenolphthalein indicator or potentiometrically.
Method principle
Weighed fat sample (2–20 g) is dissolved in solvent mixture (ethanol/diethyl ether 1:1, neutralized with KOH). Free fatty acids are titrated with standardized KOH solution (0.1 or 0.5 mol/L in ethanol) to phenolphthalein color change (colorless → pink) or to potentiometric endpoint (pH 8.5). AV [mg KOH/g] = (V × c × 56.1) / m.
Applications
- Quality control of vegetable oils (rapeseed, sunflower, olive)
- Analysis of animal fats (lard, butter)
- Monitoring fat rancidity during storage
- Quality control of frying oils (thermal degradation)
- Assessment of fat raw materials in oleochemical industry
Key parameters
| Parameter | Value |
|---|---|
| Result | Acid value [mg KOH/g] or % oleic acid |
| Range | 0.05–200 mg KOH/g |
| Limit (extra virgin olive oil) | ≤0.8% oleic acid |
| Precision (CV) | 1–3% |
| Sample mass | 2–20 g (depending on AV) |
Standard
- Standard number
- PN-EN ISO 660:2020
- Title (PL)
- Tłuszcze i oleje roślinne oraz zwierzęce — Oznaczanie liczby kwasowej i kwasowości
- Title (EN)
- Animal and vegetable fats and oils — Determination of acid value and acidity
Step-by-step procedure
-
Solvent preparation
Mix 50 mL ethanol + 50 mL ether. Add 2–3 drops phenolphthalein. Neutralize with KOH to light pink.
-
Sample weighing
Weigh fat sample (mass depends on expected AV: 20 g for AV<1, 2 g for AV>20) into conical flask.
-
Dissolution
Add 100 mL neutralized solvent. Mix until fat dissolves (heat to 40°C if needed).
-
Titration
Titrate with 0.1 mol/L KOH to persistent pink color (30 s). Record consumption with 0.05 mL accuracy.
-
Calculations
AV = (V × c × 56.1) / m [mg KOH/g]. Acidity [%] = (V × c × 28.2) / m (as oleic acid).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Burette 25 mL (class A) | Brand, DURAN, accuracy 0.05 mL | 200–500 PLN |
| Analytical balance | Mettler Toledo ME204, accuracy 0.1 mg | 5 000–15 000 PLN |
| Conical flasks 250 mL | DURAN Erlenmeyer, wide neck | 15–30 PLN/pc |
| Automatic titrator (optional) | Metrohm 888 Titrando, Mettler Toledo T5 | 15 000–35 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Potassium hydroxide KOH 0.1 mol/L in ethanol | 1310-58-3 | Standardized, for titration |
| Ethanol 96% | 64-17-5 | Solvent, neutralized with KOH |
| Diethyl ether | 60-29-7 | Solvent (1:1 with ethanol), without peroxides! |
| Phenolphthalein 1% | 77-09-8 | Indicator, solution in ethanol |
Health and safety (OHS)
- Diethyl ether — extremely flammable, may form explosive peroxides! Keep away from fire, check expiry date.
- KOH — corrosive, causes burns. Gloves and safety glasses.
- Ethanol — flammable. Fume hood recommended.
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 660:2020 — “Animal and vegetable fats and oils — Determination of acid value and acidity”.
How does this method work?
Weighed fat sample (2–20 g) is dissolved in solvent mixture (ethanol/diethyl ether 1:1, neutralized with KOH). Free fatty acids are titrated with standardized KOH solution (0.
What is the measuring range and accuracy?
Result: Acid value [mg KOH/g] or % oleic acid; Range: 0.05–200 mg KOH/g; Limit (extra virgin olive oil): ≤0.8% oleic acid; Precision (CV): 1–3%.
How long does the test take?
The times given for the individual stages add up to approximately 18 min. The procedure comprises 5 steps.
What equipment is required?
Burette 25 mL (class A), Analytical balance, Conical flasks 250 mL, Automatic titrator (optional). Indicative cost of the core instrument (Burette 25 mL (class A)): 200–500 PLN.
Where is this test used?
Quality control of vegetable oils (rapeseed, sunflower, olive); Analysis of animal fats (lard, butter); Monitoring fat rancidity during storage; Quality control of frying oils (thermal degradation); Assessment of fat raw materials in oleochemical industry.
What safety precautions apply?
Diethyl ether — extremely flammable, may form explosive peroxides! Keep away from fire, check expiry date.; KOH — corrosive, causes burns. Gloves and safety glasses.; Ethanol — flammable. Fume hood recommended.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 660.