GB 5009.229-2025National food safety standard - Determination of acid value in foods (English PDF)

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).

3.1.5 Thymophthalein (C28H30O4, CAS No.. 125-20-2).

3.1.6 Alkali blue 6B (C37H29N3O3S, CAS No.. 1324-76-1).

3.1.7 Liquid nitrogen (N2). purity > 99.99 %.

3.1.8 Petroleum ether. the boiling range is 30 °C ~ 60 °C.

3.1.9 Anhydrous sodium sulfate (Na2SO4).

3.1.10 Potassium hydroxide (KOH).

3.1.11 Sodium hydroxide (NaOH).

3.2 Preparation of reagents

3.2.1 Cold solvent. mix anhydrous ether and isopropyl alcohol (or 95 % ethanol) in a volume ratio of 1.1.

3.2.2 Phenolphthalein indicator (10 g/L). weigh 1 g of phenolphthalein, dissolve in 95 % ethanol and dilute to 100 mL.

3.2.3 Thymophthalein indicator (20 g/L). weigh 2 g of thymophthalein, dissolve in 95 % ethanol and dilute to 100 mL.

3.2.4 Alkali blue 6B indicator (20 g/L). weigh 2 g of alkali blue 6B, dissolve in 95 % ethanol and dilute to 100 mL.

3.3.1 Potassium hydroxide standard titration solution (

0.5 mol/L and

0.1 mol/L). prepared and calibrated according to the requirements of GB/T 5009.1, or purchase a standard titration solution certified by the state and awarded a standard material certificate.

3.3.2 Potassium hydroxide standard titration solution (

0.05 mol/L). before use, obtained by diluting potassium hydroxide standard titration solution (

0.5 mol/L or

0.1 mol/L), or purchase a standard titration solution certified by the state and awarded a standard material certificate.

3.3.3 Standard sodium hydroxide titration solution (

0.5 mol/L and

0.1 mol/L). prepared and calibrated according to the requirements of GB/T 5009.1 or GB/T 601, or purchase a standard titration solution certified by the state and awarded with a standard material certificate.

3.3.4 Standard sodium hydroxide titration solution (

0.05 mol/L). before use, obtained by diluting sodium hydroxide standard titration solution (

0.5 mol/L or

0.1 mol/L), or purchase a standard titration solution certified by the state and awarded with a standard material certificate.

4.1 Burette. capacity of 10 mL, minimum graduation value of

0.05 mL.

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.

5.1 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. 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.

5.3 Determination of samples Add 50 mL ~ 100 mL of cold solvent to the weighed oil and fat sample, shake the sample gently until it is completely dissolved, add 3 ~ 4 drops of phenolphthalein indicator, and immediately titrate with potassium hydroxide or sodium hydroxide standard titration solution of the concentration specified in Table 1 until the solution turns slightly red and does not fade for 15 s, which is the end point. Perform a blank test at the same time (if the cold solvent is adjusted to neutral with a standard titration solution before the sample is determined, V0 = 0 mL).

9.1 Reagents

9.2 Preparation of reagents Cold solvent. mix anhydrous ether and isopropyl alcohol (or 95 % ethanol) in a volume ratio of 1.1.

9.3 Preparation of standard solutions Same as 3.3.