GB/T 5009.37-2003Method for analysis of hygienic standard of edible oils (English PDF)

3.1 Color

3.2 Smell and taste

POUR the specimen into a 150 mL beaker, PLACE it in a water bath, HEAT it to 50 °C, USE a glass rod to stir it rapidly. SMELL its odor, TAKE a small amount of specimen, TASTE it, DESCRIBE it using such wording as normal, scorching, rancid, bitter and spicy.

4.1 Acid value

4.1.1 Principle

Free fatty acid in vegetable oil is titrated by potassium hydroxide standard solution, the milligrams of potassium hydroxide consumed per gram of vegetable oil is known as the acid value.

4.1.2 Reagents

4.1.4 Result calculation

The acid value of the specimen is calculated in accordance with formula (1).

4.2 Peroxide value

4.2.1 Method I -- Titration method

4.2.1.1 Principle

Peroxide is produced in the oxidation of oil, peroxide reacts with the potassium iodine to produce free iodine, which is titrated by sodium thiosulfate solution, the content is calculated.

4.2.1.2 Reagents

4.2.1.3 Analytical procedures

WEIGH 2.00 g ~ 3.00 g of uniformly mixed specimen (filter it if necessary), PLACE it into a 250 mL iodine bottle, ADD 30 mL of chloroform - glacial acetic acid mixed solution, to make the specimen completely dissolved. ADD 1.00 mL of saturated potassium iodide solution, tightly PLUG the bottle, gently SHAKE it for 0.5 min, then PLACE it in the dark for 3 min. TAKE it out, ADD 100 mL of water, SHAKE it uniformly, immediately USE the sodium thiosulfate standard titration solution (0.0020 mol/L) to titrate it; when it becomes light yellow, ADD 1 mL of starch indicator solution, CONTINUE titration until the blue color disappears as the end, TAKE the chloroform - glacial acetic acid solution, potassium iodide solution, water of the same amount, USE the same method to make the reagent blank test.

4.2.1.4 Calculation results

The peroxide value of the specimen is calculated in accordance with the formula (2) and (3).

4.2.1.5 Precision

The absolute difference between two independent determinations obtained under repeatability conditions shall not exceed 10% of the arithmetic mean.

4.2.2 Method II -- Colorimetric method

4.2.2.1 Principles

The specimen is dissolved by chloroform - methanol mixed reagent, the ferrous ion in the specimen is oxidized into the ferric ion, which reacts with the thiocyanate to produce yellow red iron thiocyanate complex. The absorbance is measured at the wavelength 500 nm, which is compared with the standard series for quantification.

4.2.2.2 Reagent

4.2.2.2.1 Hydrochloric acid solution (10 mol/L). accurately MEASURE 83.3 mL of concentrated hydrochloric acid, ADD water to dilute it to 100 mL, MIX it uniformly.

4.2.2.2.7 Iron standard use solution (0.01 g/L). PIPETTE 1.0 mL of iron standard stock solution (1.0 mg/mL) into a 100 mL volumetric flask, ADD the chloroform + methanol (7 + 3) mixed solvent to dilute it to the mark, MIX it uniformly, each milliliter of this solution is equivalent to 10.0 µg of iron.

4.2.2.3 Instruments

4.2.2.3.1 Spectrophotometer.

4.2.2.3.2 10 mL glass colorimetric tube with plug.

4.2.2.4 Analytical procedures

4.4 Free gossypol (applicable to cottonseed oil)

4.4.1 UV spectrophotometry

4.4.1.1 Principles

The free gossypol in the specimen is extracted by acetone, the maximum absorption occurs at 378 nm, the absorption value is proportional to the gossypol content within a certain range, it is compared with the standard series for quantification.

4.4.1.2 Instruments

UV spectrophotometer.

4.4.1.3 Reagents

4.4.1.3.1 Acetone (70%). ADD water to dilute 350 mL of acetone to 500 mL.

4.4.1.3.2 Gossypol standard solution. Accurately WEIGH 0.1000 g of gossypol, PLACE it into a 100 mL volumetric flask, ADD acetone (70%) to dissolve it and dilute it to the mark. Each milligram of this solution is equivalent to 1.0 mg of gossypol.

4.10.2 Mineral oil

TAKE 1 mL of specimen, PLACE it in the conical flask, ADD 1 mL of potassium hydroxide solution (600 g/L) and 25 mL of ethanol, CONNECT the air condensing tube for backflow saponification for about 5 min, SHAKE it during saponification to heat it uniformly. After saponification, ADD 25 mL of boiling water, SHAKE it uniformly, if there is turbid or oil substance precipitation, it is indicated that there is mineral oil which cannot be saponified.

4.10.3 Hemp oil

TAKE 10 µL of specimen and 10 µL of reference hemp oil, respectively, PLACE the specimen onto the silica gel G thin plate, which is about 0.25 mm ~ 0.3 mm in thickness, ACTIVATE it at 105 °C for 30 min. If the oil is too thick, USE 5 times benzene to dilute it, ADD specimen again, the addition amount is about 10 µL ~ 20 µL. The developing agent is benzene, the color developer is fast blue salt B solution (1.5 g/L) (prepare it before use). When the spot, reference color and RF value are equivalent, it is indicated that there is hemp oil. The flax oil, sesame oil, and fast blue B salt are also in red, BUT they have smaller RF value on the thin plate.

4.11 Aflatoxins

OPERATE in accordance with GB/T 5009.22. […]