SAMPLING A N D ANALYSIS OF COMMERCIAL FATS A N D OILS
AOCS Official Method Ca 2c-25 Reapproved 1997
'Moisture and Volatile Matter Air Oven Method
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DEFINITION This method determines the moisture and any other material volatile under the conditions of the test. SCOPE Applicable to animal and vegetable fats, but not to drying or semidrying oils or oils of the coconut group. It is not applicable to fats containing added monoglycerides.
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APPARATUS 1. Air oven-AOCS Specification H 3-45. 2. Aluminum moisture dishes-minimum 30 gauge, approximately 50 x 20 mm, with tight-fitting slip-over covers; Sargent-Welch (20 mL WLS 25725-B, 50 mL WLS 25725-D), or equivalent (see Notes, I). 3. Desiccator-containing an efficient desiccant. Calcium chloride is not satisfactory. See AOCS Specification H 9-87. PREPARATION O F SAMPLE I. Because water tends to settle in samples that have softened or melted. care must be taken to mix sam~lesthoroughly so as to distribute the water uniformiy. Soften with gentle heat (do not melt) and mix thoroughly with an efficient mixer. PROCEDURE I . Weigh accurately 5 g of sample into a tared moisture dish that has been dried and cooled previously in a desiccator.
2. Place in air oven and dry for 30 min at 130 + I "C. Remove from the oven, cool to room temperature in a desiccator and weigh. 3. Repeat Procedure, 2 until the loss in weight does not exceed 0.05% per 30-min drying period. CALCULATIONS 1. Moisture and volatile matter, % = loss in mass, g x 100 mass of sample, g NOTES I . For samples with high moisture and volatile content, the use of lightweight, coverless, disposable weighing dishes is not permitted. Erroneously high results may be obtained due to oil loss from splattering during heating.
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SAMPLING A N D ANALYSIS OF COMMERCIAL FATS A N D OILS
AOCS Official Method Ca 5a-40 Reapproved 1997
CP
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. APPARATUS I . Oil sample bottles-I15 or 230 mL (4 or 8 oz), or 250mL Erlenmeyer flasks.
(a) Free fatty acids as oleic, % = mL of alkali x N x 28.2 mass, g of sample
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 I for the appropriate normality of the sodium hydroxide solution, depending on the expected free fatty acid concentration range in the sample.
(b) Free fatty acids as lauric,% = mL of alkali x N x 20.0 mass, g of sample
Table 1 Free fatty acid range, alcohol volume and strength of alkalia
FFA range (%) Sample (g)
Alcohol (mL) Strength of alkali
(c) Free fatty acids as palmitic, % = mL of alkali x N x 25.6 mass, g of sample 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. 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
"FFA, free fatty acid; N, normality.
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PROCEDURE I . 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 I to determine the sample 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 exp6sed as lauric acid and in palm oil in terms of palmitic acid.
Approximate FFA value (%) R
,
-
-
-
-
0-0.05
0.05-0.1
0.1- 1.0
1.0-2.0
0.007
0.0 10 12.73 0.03
0.046 9.90 0.13 .,
0.073 4.75 0.20
RSD (CV, %) 33.93 R (95%)= 2.8 x SR 0.02
"Values obtained from the AOCS Smalley 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 oilsa
Approximate FFA value (%) R
RSD (CV, 9%) R (95%)= 2.8 x S ,
0.1-1 .O
1 .O-2.0
0.077 14.57 0.22
0.156 9.84 . 0.44
"Values obtained from the AOCS Smalley Laboratory Proficiency Program.
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SAMPLING A N D ANALYSIS O F COMMERCIAL FATS A N D OILS
AOCS Official Method Ca 3a-46 Replacing Ca 3-25 and Ca 3-46
Reapproved 1997
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Insoluble impurities" DEFINITION This method determines dirt, meal and other foreign substances insoluble in kerosene and petroleum ether. SCOPE Applicable to all normal fats and oils. APPARATUS 1. Gooch crucible--prepared with a glass-fiber filter without organic filler (Reeve Angel 934 AH or WhatmanJ GF/C). Wash the filter with y , ~ x , all;l2b& and e h s Dry to constant weight at I0 I k 1"C Cool in a desiccator to room temperature and weigh. J 2. Filter flask of convenient size ahd Gooch crucible v adapter.
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3. Filter through the prepared Gooch crucible with the aid of a vacuum. Wash with five 10-mL portions of hot kerosene, allowing each portion to drain before adding the next. 4. Wash thoroughly with petroleum ether to remove all of the kerosene. Dry the crucible and contents to a constant weight at 101 k 1°C. cool to room temperature in a desiccator and weigh.
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REAGENTS (see Notes, Caution) 1. Petroleum ether-AOCS Specification H 2-41. 2. Kerosene-refined petroleum distillate with a flash point not below 23°C (75°F). as determined by the American Society for Testing and Materials Standard Method D56, using the tag closed tester. The kerosene should be filtered through a Gooch crucible, prepared as in Apparatus, I, before using. PREPARATION O F SAMPLE 1. Samples must be mixed thoroughly. If necessary, soften with gentle heat (do not melt) and mix thoroughly with an efficient mixer.
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PROCEDURE 1. Use the residue from the moisture and volatile matter determination (AOCS Official Methods Ca 2b-38 or Ca 2d-25), or a sample prepared in the same manner (see Notes, I). 2. Add 50 mL of kerosene to the residue.and heat in a water bath to dissolve the fat.
CALCULATIONS 1. Insoluble impurities, % = gain in mass.of crucible x loo mass of sample taken for moistvre NOTES Caution Petroleum ether and kerosene are flammable solvents. A fume hood should be used at all times when working with these solvents. NUMBERED NOTES . I . Samples (e.g., certain feed stocks) with a higher than usual percentage of insoluble impurities may be difficult, if not impossible, to filter. A study among five laboratories indicated that, for such samples, a 2-g subsample (rather than a 5-g subsample as specified in AOCS Ofticial Methods Ca 2b-38 and c a 2d-25) can be used without greatly affecting the precision of the method.
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