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This standard replaces Section 4.1, GB/T 5009.37-2003 Method for Analysis of Hygienic Standard of Edible Oils, meanwhile, it replaces Section 14.3, GB/T 5009.44-2003 Method for Analysis of Hygienic Standard of Meat and Meat Products, Sections 4.1, 4.2 and 4.3, GB/T 5009.56-2003 Method for Analysis of Hygienic Standard of Pastry, Section 4.1, GB/T 5009.77-2003 Method for Analysis of Hygienic Standard of Edible Hydrogenated Oil and Margarine, GB/T 15689-2008 Oilseeds - Determination of Acidity of Oils, GB/T 14489.3-1993 Method for Determination of Free Fatty Acids Content of Oils in Oilseeds and GB/T 5530-2005 Animal and Vegetable Fats and Oils - Determination of Acid Value and Acidity.
The following main changes have been made with respect to Section 4.1, GB/T 5009.37-2003 (the previous edition).
——The standard name is revised as "National Food Safety Standard - Determination of Acid Value in Foods";
——The application scope of this standard is modified;
——The phenolphthalein indicator titration method is modified as Method I, i.e. cold solvent indicator titration method;
——The automatic potentiometric titration method with cold solvent is added as Method II;
——The hot ethanol indicator titration method is added as Method III;
——The specimen preparation criterion of food sample is added;
——The requirements of sampling weight are added;
——The requirements of precision are modified.
National Food Safety Standard - Determination of Acid Value in Foods
1 Scope
This standard specifies three kinds of determination methods for acid value in various foods - cold solvent indicator titration method (Method I), automatic potentiometric titration method with cold solvent (Method II) and hot ethanol indicator titration method (Method III).
Method I is applicable to edible oil samples that can be fully dissolved into clear solutions by cold solvent at normal temperature; application scope of this method covers 7 categories, i.e., edible vegetable oil (except capsicol), edible animal oil, edible hydrogenated oil, shortening, margarine, non-dairy whipped topping and vegetable oil material.
Method II is applicable to oil samples extracted from edible oil sample and oleaginous food that can be fully dissolved into clear solutions by cold solvent at normal temperature; the application scope of this method covers 19 categories, i.e., edible vegetable oil (including capsicol), edible animal oil, edible hydrogenated oil, shortening, margarine, non-dairy whipped topping, vegetable oil material, fried snack foods, puffed food, roasted nuts, nut foods, pastries, breads, biscuits, fried instant noodles, sauce made from nuts and seeds, animal dried aquatic products, cured meat products and chilli sauce with edible oil added.
Method III is applicable to edible oil samples unable to be fully dissolved into clear solutions by cold solvent at normal temperature; the application scope of this method covers 6 categories, i.e., edible vegetable oil, edible animal oil, edible hydrogenated oil, shortening, margarine and non-dairy whipped topping.
Method I Cold Solvent Indicator Titration Method
2 Theory
Dissolve the oil specimen into sample solution with organic solvent, neutralize and titrate the free fatty acid in sample solution with potassium hydroxide or sodium hydroxide standard titration solution, judge the titration end point according to the corresponding color change of indicator, and calculate the acid value of oil specimen according to the volume of standard titration solution consumed at titration end point.
3 Reagents and Materials
Unless otherwise specified, analytically-pure reagents and Class-III water (defined in GB/T 6682) are adopted for the purpose of this method.
3.1 Reagents
3.1.1 Isopropanol (C3H8O).
3.1.2 Ethyl ether (C4H10O).
3.1.3 Methyl tertlary butyl ether(C5H12O).
3.1.4 95% ethyl alcohol (C2H6O).
3.1.5 Phenolphthalein (C20H14O4); indicator; CAS: 77-09-8.
3.1.6 Thymolphthalein (C28H30O4); indicator; CAS: 125-20-2.
3.1.7 Alkali blue 6B (C37H31N3O4); indicator; CAS: 1324-80-7.
3.1.8 Anhydrous sodium sulfate (Na2SO4), sufficiently dried at 105℃~110℃, and then filled in closed container for cooling and preserving.
3.1.9 Anhydrous diethyl ether (C4H10O).
3.1.10 Petroleum ether, with boiling range of 30℃~60℃.
3.2 Reagent preparation
3.2.1 Potassium hydroxide or sodium hydroxide standard titration aqueous solution, with concentration of 0.1mol/L or 0.5mol/L, prepared and calibrated according to those specified in GB/T 601, and commercially available reagents may also be purchased.
3.2.2 Ethyl ether-isopropanol mixture: ethyl ether + isopropanol=1+1, mutually dissolve and mix 500mL of ethyl ether and 500mL of isopropanol; it shall be prepared immediately before use.
3.2.3 Phenolphthalein indicator: weigh 1g of phenolphthalein, add it into 100mL of 95% ethyl alcohol, stir until it is fully dissolved.
3.2.4 Thymolphthalein indicator: weigh 2g of thymolphthalein, add it into 100mL of 95% ethyl alcohol, stir until it is fully dissolved.
3.2.5 Alkali blue 6B indicator: weigh 2g of alkali blue 6B, add it into 100mL of 95% ethyl alcohol, stir until it is fully dissolved.
4 Apparatuses
4.1 10mL micro burette: with minimum scale of 0.05mL.
4.2 Balance: with sensitivity of 0.001g.
4.3 Thermostat water bath cauldron.
4.4 Thermostatic drying chamber.
4.5 Centrifuger: with maximum rotation speed not less than 8,000r/min.
4.6 Rotary evaporator.
4.7 Soxhlet fat extractor.
4.8 Vegetable oil material pulverizer or grinder.
5 Analysis Steps
5.1 Specimen preparation
5.1.1 Edible oil specimen preparation
If edible oil sample is in clear liquid state at normal temperature, mix it uniformly and sample directly, otherwise, carry out impurity removal and dewatering and drying treatments according to the requirements of Annex A; if edible oil sample is in solid state at normal temperature, prepare according to Annex B; if the sample is emulsified edible oil, prepare according to Annex C.
5.1.2 Vegetable oil material specimen preparation
Pulverize the vegetable oil material into homogeneous fine particles with pulverizer or grinder, vegetable oil materials with high fragility (such as soybean, sunflower seed, cotton seed, rape seed, etc.) shall be pulverized into fine particles with particle size of 0.8mm ~3mm or smaller, and those with low fragility (such as copra, palm kernel, etc.) shall be pulverized into particles with particle size not greater than 6mm. in case heat is generated obviously during pulverization, pulverize according to D.3, Annex D.
Take pulverized fine particles of vegetable oil material and fill them into Soxhlet fat extractor, add an adequate amount of extraction solvent (3.1.9 or 3.1.10), heat and carry out reflux extraction for 4h. Finally, collect all the extracting solutions and combine them into a flask, put the flask into rotary evaporator with the water bath temperature not higher than 45℃, thoroughly evaporate the solvent to dryness through rotating under the negative pressure conditions of 0.08MPa ~ 0.1 MPa, and take the residual liquid oil as the specimen for acid value determination.
If the residual liquid fat is turbid, emulsified, layered or with precipitate, impurity removal and dewatering and drying treatments shall be carried out according to the requirements of Annex A.
5.2 Specimen weighing
Weigh the specimen based on color and estimated acid value of prepared specimen and according to those specified in Table 1.
Table 1 Specimen-weighing Table
Estimated acid value
mg/g Minimum sampling weight of specimen g Concentration of used titrating solution mol/L Specimen weighing accuracy
g
0~1 20 0.1 0.05
1~4 10 0.1 0.02
4~15 2.5 0.1 0.01
15~75 0.5~3.0 0.1 or 0.5 0.001
>75 0.2~1.0 0.5 0.001
Specimen sampling weight and titrating solution concentration shall be such that the consumption volume of titrating solution is within the range of 0.2mL ~10mL (after deducting the blank). If the actual sampling weight of sample is inconsistent with the value corresponding to the sample acid value after inspection, retest shall be carried out according to the requirements of Table 1 after adjusting the sampling weight.
5.3 Specimen determination
Take a 250 mL clean conical flask, weigh the prepared oil specimen with balance according to the requirements of Section 5.2 and express the mass (m) in gram. Add 50mL~100mL of ethyl ether-isopropanol mixture and 3~4 drops of phenolphthalein indicator, sufficiently shake to dissolve the specimen. Carry out manual titration for the specimen solution with scale burette filled with standard titration solution (3.2.1), and it is regarded as the titration end point when the specimen solution takes on reddish color and does not fade obviously within 15s. Immediately stop titrating, and record the volume of standard titration solution (in milliliter) consumed in this titration as V.
As for oil sample with dark color, thymolphthalein indicator or alkali blue 6B indicator may be used to replace phenolphthalein indicator; during titration, it is regarded as the titration end point of thymolphthalein when the color turns to blue and it is regarded as the titration end point of alkali blue 6B indicator when the color turns to red from blue. Only alkali blue 6B indicator can be used in cold solvent indicator method for determining the acid value of rice oil.
5.4 Blank test
Take another 250 mL clean conical flask, and accurately add organic solvent mixture (3.2.2) and indicator (3.2.3, 3.2.4 or 3.2.5) with the same volume and kind as that used in specimen determination in Section 5.3, and shake well. Carry out manual titration with scale burette filled with standard titration solution (3.2.1), and it is regarded as the titration end point when the solution takes on reddish color and does not fade obviously within 15s. Immediately stop titrating, and record the volume of standard titration solution (in milliliter) consumed in this titration as V0.
As for cold solvent indicator titration method, dropwise add several drops of indicator (3.2.3, 3.2.4 or 3.2.5) into prepared specimen dissolving solution (3.2.2), titrate the specimen dissolving solution with standard titration solution (3.2.1) until corresponding color change appears without obvious fading within 15s, and it indicates that the acidity of specimen dissolving solution is just neutralized. Then dissolve the oil specimen by using the specimen dissolving solution with its acidity neutralized, and continue to titrate the specimen solution with the same method until corresponding color appears without obvious fading within 15s, record the volume of the standard titration solution (in milliliter) consumed in this titration as V, and it is unnecessary to carry out blank test, i.e., V0=0.
Foreword i
1 Scope
2 Theory
3 Reagents and Materials
4 Apparatuses
5 Analysis Steps
6 Expression of Analysis Results
7 Precision
8 Theory
9 Reagents and Materials
10 Apparatuses
11 Analysis Steps
12 Expression of Analysis Results
13 Precision
14 Theory
15 Reagents and Materials
16 Apparatuses
17 Analysis Steps
18 Expression of Analysis Results
19 Precision
Annex A Impurity Removal, Drying and Dewatering of Oil Specimen
Annex B Treatment of Solid-state Oil Specimen
Annex C Treatment of Emulsified Oil Specimen
Annex D Sample Pulverization
Annex E Schematic Diagram for Judgment of Titration End Point of Automatic Potentiometric Titration Method
