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AOCS Official Method Ca 5a-40
Reapproved 2009
Free Fatty Acids
DEFINITION
This method determines the free fatty acids existing in the sample.
SCOPE
Applicable to all crude and refined vegetable oils, marine oils and animal fats.
SAMPLING AND ANALYSIS OF COMMERCIAL FATS AND OILS
APPARATUS
1. Oil sample bottles—115 or 230 mL (4 or 8 oz), or 250 mL Erlenmeyer flasks.
REAGENTS
1. Ethyl alcohol, 95%—USSD formulas 30 and 3A are permitted (see Notes, 1). The alcohol must give a definite, distinct and
sharp end point with phenolphthalein and must be neutralized with alkali to a faint, but permanent pink color just before
using.
2. Phenolphthalein indicator solution—1% in 95% alcohol.
3. Sodium hydroxide solution—accurately standardized. See AOCS Specification H 12-52. See Table 1 for the appropriate
normality of the sodium hydroxide solution, depending on the expected free fatty acid concentration range in the sample.
PROCEDURE
1. Test samples must be well mixed and entirely liquid before weighing; however, do not heat the sample more than 10°C over
the melting point.
2. Use Table 1 to determine the test portion weight for various ranges of fatty acids. Weigh the designated sample size into an
oil sample bottle or Erlenmeyer flask (see Notes, 2).
3. Add the specified amount of hot neutralized alcohol and 2 mL of indicator.
4. Titrate with standard sodium hydroxide, shaking vigorously until the appearance of the first permanent pink color of the
same intensity as that of the neutralized alcohol before the addition of the sample. The color must persist for 30 seconds.
CALCULATIONS
1. The percentage of free fatty acids in most types of fats and oils is calculated as oleic acid, although in coconut and palm
kernel oils it is frequently expressed as lauric acid and in palm oil in terms of palmitic acid.
(a) Free fatty acids as oleic, % = mL of alkali M 28.2
mass, g of test port
× ×
iion
(b) Freefatty acids as lauric, % =
mL of alkali M 20.0
mass, g of test port
× ×
iion
(c) Free fatty acids as palmitic, % = mL of alkali M 25.6
mass, g of test port
× ×
iion
2. The free fatty acids are frequently expressed in terms of acid value instead of percentage free fatty acids. The acid value is
defined as the number of milligrams of KOH necessary to neutralize 1 g of sample. To convert percentage free fatty acids (as
oleic) to acid value, multiply the percentage free fatty acids by 1.99.
PRECISION
Precision data for refined, bleached and deodorized oils are shown in Table 2. Precision data for crude oils are shown in Table 3.
NOTES
1. Isopropanol, 99%, may be used as an alternate solvent with crude and refined vegetable oils.
2. Cap bottle and shake vigorously for 1 min if oil has been blanketed with carbon dioxide gas.
REFERENCES
See J. Assoc. Off. Anal. Chem. 59:658 (1976) regarding the ruggedness of this method.
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Page 2 of 2
SAMPLING AND ANALYSIS OF COMMERCIAL FATS AND OILS
Ca 5a-40 • Free Fatty Acids
Table 1
Free fatty acid range, alcohol volume and strength of alkalia
FFA range (%) Test portion (g) Alcohol (mL) Strength of alkali
0.00 to 0.2 56.4 ± 0.2 50 0.1 M
0.2 to 1.0 28.2 ± 0.2 50 0.1 M
1.0 to 30.0 7.05 ± 0.05 75 0.25 M
30.0 to 50.0 7.05 ± 0.05 100 0.25 or 1.0 M
50.0 to 100 3.525 ± 0.001 100 1.0 M
aFFA, free fatty acid; N, normality.
Table 2
The average, expected between-laboratory variation (standard deviation of
reproducibility, SR) for the determination of free fatty acids in refined, bleached
and deodorized oilsa
Approximate FFA value (%) 0–0.05 0.05–0.1 0.1–1.0 1.0–2.0
SR 0.007 0.010 0.046 0.073
RSD (CV, %) 33.93 12.73 9.90 4.75
R (95%) = 2.8 × SR 0.02 0.03 0.13 0.20
aValues obtained from the AOCS Laboratory Proficiency Program.
Table 3
The average, expected between-laboratory variation (standard deviation of
reproducibility, SR) for the determination of free fatty acids in crude oils
a
Approximate FFA value (%) 0.1–1.0 1.0–2.0
SR 0.077 0.156
RSD (CV, %) 14.57 9.84
R (95%) = 2.8 × SR 0.22 0.44
aValues obtained from the AOCS Laboratory Proficiency Program.
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