GB 5009.229-2025 PDF English (GB 5009.229-2016: Older version)

GB5009.229-2025: PDF in English

GB 5009.229-2025 GB NATIONAL STANDARD OF THE PEOPLE’S REPUBLIC OF CHINA National food safety standard - Determination of acid value in food ISSUED ON. MARCH 16, 2025 IMPLEMENTED ON. SEPTEMBER 16, 2025 Issued by. National Health Commission of the People’s Republic of China; State Administration for Market Regulation. Table of Contents Foreword... 3 1 Scope... 4 First method -- Cold solvent indicator titration method... 4 2 Principle... 4 3 Reagents and materials... 4 4 Instruments and equipment... 6 5 Analysis steps... 6 6 Expression of analysis results... 8 7 Precision... 9 Second method -- Cold solvent automatic potentiometric titration... 9 8 Principle... 9 9 Reagents and materials... 9 10 Instruments and equipment... 10 11 Analysis steps... 10 12 Expression of analysis results... 12 13 Precision... 12 Third method -- Hot ethanol indicator titration method... 12 14 Principle... 12 15 Reagents and materials... 12 16 Instruments and equipment... 13 17 Analysis steps... 13 18 Expression of analysis results... 14 19 Precision... 14 Forth method -- Spectrophotometry... 14 20 Principle... 14 21 Reagents and materials... 14 22 Instruments and equipment... 15 23 Analysis steps... 16 24 Expression of analysis results... 19 25 Precision... 19 26 Others... 19 Annex A Impurity removal and drying and dehydration of oil and fat samples... 21 Annex B Schematic diagram of titration end point determination by automatic potentiometric titration method... 23 National food safety standard - Determination of acid value in food 1 Scope This Standard specifies the determination methods for acid value in food. The first, second and third methods are applicable to the determination of acid value in food [except non-dairy cream, powdered oils and fats, margarine, compound seasonings (mayonnaise, salad dressing, oil-based chili sauce, nut and seed sauce, hot pot base and other semi-solid seasonings)]. The fourth method is applicable to the determination of acid value in non-dairy cream, powdered oils and fats, margarine, compound seasonings (mayonnaise, salad dressing, oil-based chili sauce, nut and seed sauce, hot pot base and other semi-solid seasonings). First method -- Cold solvent indicator titration method 2 Principle Based on the principle of acid-base neutralization reaction, potassium hydroxide or sodium hydroxide standard titration solution is used to neutralize the free fatty acids in the sample solution, and the titration end point is determined by the acid-base indicator. The acid value of the sample is calculated based on the consumption of the standard titration solution. 3 Reagents and materials Unless otherwise specified, the reagents used in this method are analytically pure, and the water is grade 3 water specified in GB/T 6682. 3.1 Reagents 3.1.1 Isopropyl alcohol (C3H8O). 3.1.2 Anhydrous ether (C4H10O). 3.1.3 95 % ethanol (C2H5OH). 3.1.4 Phenolphthalein (C20H14O4, CAS No.. 77-09-8). 4 Instruments and equipment 4.1 Burette. capacity of 10 mL, minimum graduation value of 0.05 mL. 4.2 Burette. capacity of 25 mL or 50 mL, minimum graduation value of 0.1 mL. 4.3 Balance. the sensitivity is 0.01 g and 0.001 g respectively. 4.4 Food grinder or pounder. 4.5 Laboratory oil press. screw press, non-heating type. 4.6 Porcelain mortar. 4.7 Constant temperature water bath. 4.8 Constant temperature blast drying oven. 4.9 Centrifuge. speed ≥ 8000 r/min. 4.10 Rotary evaporator or equivalent equipment. 4.11 Soxhlet extraction device. 5 Analysis steps 5.1 Preparation of samples 5.1.1 Animal and vegetable oils and fats, edible hydrogenated oils, shortening, cocoa butter substitutes At room temperature, liquid samples are fully mixed and then directly sampled for testing. For solid (or semi-solid) samples, take a representative sample and place it in a warm water bath or a constant temperature blast drying oven to heat and melt, mix well and then take the oil and fat for testing. If the oil and fat sample is obviously turbid, emulsified, stratified or precipitated, it shall be treated with impurity removal and dehydration according to Annex A. 5.1.2 Vegetable oils, nuts and seeds Direct pressing method is used for samples susceptible to lipase, such as raw and dried sesame. Take a representative sample, use laboratory oil press to press at room temperature, collect the squeezed material and filter it with filter paper immediately, and then take the oil and fat for determination. Soxhlet extraction method is used for other samples. For samples with shells, peel off the shell first and keep the edible part. Among them, the kernels with green inner membrane (such as pumpkin seeds, melon seeds, etc.) shall also remove the green inner membrane attached to the surface of the kernels (the method of removing the green inner membrane is to spray the surface of the shelled kernels with laboratory water to moisten, rub off the green inner membrane, and then place the kernels with the green inner membrane removed in a 50 ℃ constant temperature blast drying oven for 45 min to dry). The sample is fully crushed with a food grinder, pounder or porcelain mortar. If the sample is obviously heated during the crushing process, it shall add an appropriate amount of liquid nitrogen and carry out the crushing in a frozen state. After the sample is prepared, it shall immediately pack the crushed sample with a filter paper tube and place it in a Soxhlet extraction device, add anhydrous ether or petroleum ether from the upper end of the condenser tube of the extraction device to two-thirds of the bottle volume, and heat and extract in a water bath for 4 h. Recover the extract in a flask, place it in a rotary evaporator with a water bath temperature not higher than 40 ℃, evaporate the organic solvent under reduced pressure, and use the residue as an oil and fat sample for acid value determination. If the residue is obviously turbid, emulsified, stratified or precipitated, it shall be treated with impurity removal and dehydration according to Annex A. 5.1.3 Other foods containing fats and oils Take the edible part of a representative sample (samples with more water content can be drained with gauze first), and use a food grinder, pounder or porcelain mortar to fully crush the sample (so that the free fat in the sample can be fully extracted by petroleum ether). If the sample is obviously heated during the crushing process, it shall add an appropriate amount of liquid nitrogen and carry out the crushing in a frozen state. Place the crushed sample in a wide-mouth bottle (samples with more water content can be dehydrated by adding an appropriate amount of anhydrous sodium sulfate), add 2 ~ 3 times the volume of petroleum ether, stir and mix, seal and extract for more than 12 h. After stirring, let it stand for a while, filter through a funnel filled with anhydrous sodium sulfate, take the filtrate; in a water bath not higher than 40 ℃, use a rotary evaporator to evaporate the petroleum ether under reduced pressure, and use the residue as an oil and fat sample for acid value determination. If the residue is obviously turbid, emulsified, stratified or precipitated, it shall be treated with impurity removal and dehydration according to Annex A. 5.2 Weighing of samples According to the estimated acid value of the sample, weigh the oil and fat sample according to the sample weight specified in Table 1 and place it in a 250 mL conical flask. According to the estimated acid value of the sample, weigh the oil and fat sample according to the sample weight specified in Table 1 and place it in a 200 mL beaker. 11.3 Determination of samples Add 50 mL ~ 100 mL of cold solvent to the weighed oil and fat sample, then add a polytetrafluoroethylene magnetic stirrer, and place the sample on a magnetic stirrer to stir and dissolve. Then, insert the electrode and burette connected to the automatic potentiometric titrator into the sample solution. Note that the glass bulb of the electrode and the anti-diffusion head of the burette shall be completely immersed below the liquid surface of the sample solution and it shall avoid touching the inner wall of the beaker. Start the automatic potentiometric titrator and titrate with potassium hydroxide or sodium hydroxide standard titration solution. The reference conditions of the automatic potentiometric titrator are as follows. - Minimum liquid addition volume. 0.01 mL ~ 0.06 mL. - Maximum liquid addition volume. 0.1 mL ~ 0.5 mL. - Signal drift. 20 mV ~ 30 mV. - Start the automatic monitoring function to automatically plot the corresponding pH-titration volume change curve and the corresponding first-order differential curve in real time, as shown in Annex B. - End point determination method. The titration end point is the point indicated by the peak of the first-order differential curve caused by the “pH jump” on the “S”- shape pH-titration volume real-time change curve generated when the free fatty acids undergo neutralization reaction (as shown in Figure B.1 in Annex B). After the titration end point, the automatic potentiometric titrator will automatically stop titration, the titration ends, and the volume of the consumed standard titration solution will be automatically displayed. During the titration process, if there are multiple “pH jumps” in the oil and fat sample (such as rice bran oil, etc.), the titration end point is the “pH jump” with the pH at the starting point of the “jump” that is most consistent with or close to the pH range of 7.5 ~ 9.5 (as shown in Figure B.2); if a “direct jump” type pH-titration volume change curve is generated, the titration end point is the peak of the corresponding first-order differential curve (as shown in Figure B.3); if multiple first-order differential peaks are generated on a “pH jump”, the titration end point is the highest peak.......
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