Food additive - Determination of citric acid fatty acid glycerides

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A. 1 General regulations

Unless otherwise specified in this standard, the purity of the reagents used should be above analytical purity. The standard titration solution used, the standard solution for impurity determination, the formulation, and the product should be prepared in accordance with the provisions of GB/T601, GB/T602, and GB/T603. The experimental water should comply with the provisions of Grade III water in GB/T6682-2008. The solution used in the experiment refers to aqueous solution when no specific solvent is specified for preparation

A.2 Identification test

Insoluble in cold water, dispersible in hot water, soluble in oil, insoluble in cold ethanol.

A.3 Determination of Sulfuric Acid Ash

A.3.1 Analysis Steps

Weigh 2g of the sample, accurate to 0.0001g, and place it in a crucible that has been burned to constant weight at 800 ℃± 25 ℃. Add a small amount of sulfuric acid and slowly heat until the sample is completely evaporated or carbonized. Continue heating until the sulfuric acid vapor escapes, and burn in a high-temperature furnace at 800 ℃± 25 ℃ until constant weight

A.3.2 Result Calculation

Calculate the mass fraction w1 of sulfuric acid ash according to equation (A.1):

Where:

m1- the mass of the crucible and residue after ignition, in grams (g)

m0- Mass of the crucible, in grams (g)

m - The mass of the sample, in grams (g)

A.4 Determination of free glycerol

A.4.1 Reagents and solutions

A.4.1.1  Glacial acetic acid

A.4.1.2; Chloroform

A.4.1.3; Periodic acid solution: Dissolve 5.4g of periodic acid in a mixture of 100mL of water and 1900mL of glacial acetic acid, mix well, and store in a stoppered glass bottle away from light

A.4.1.4; Potassium iodide solution: 150g/L

A.4.1.5; Sodium thiosulfate standard titration solution: c (Na2S2O3)=0.1mol/L

A.4.1.6 Starch indicator solution: 10g/L

A.4.2 Analysis Steps

A.4.2.1 Preparation of Sample Solution

First melt the sample (at a temperature not exceeding its melting point of 10 ℃) and thoroughly mix. Accurately weigh 1g of the mixed sample to the nearest 0.001g, place it in a 100mL volumetric flask, add 50mL of trichloromethane to dissolve it, then add 25mL of water, seal with a stopper, shake vigorously for 30-60s, and then let it stand to separate the trichloromethane from the aqueous phase (if it forms a cloudy state, 3mL or 4mL of glacial acetic acid can be added for demulsification). Use a glass siphon to transfer the aqueous phase to another 100mL volumetric flask. Extract the trichloromethane solution three times with 25mL, 25mL, and 20mL of water, respectively. Concentrate the extracted aqueous phase into the same volumetric flask, add water to a constant volume of 100mL, mix well, and this is the sample solution

A.4.2.2 Determination

Prepare two 500mL iodine measuring flasks and add 50mL periodate solution to each.

. Transfer 50mL of sample solution (A.4.2.1) and place it in one of the iodine measuring bottles. Transfer 50mL of water and place it in another iodine measuring bottle for blank testing. Shake well and let stand for 30 to 90 minutes. Add 20mL of potassium iodide solution to each iodine measuring bottle, carefully shake well, and let stand in a dark place for 1-5 minutes. Add 100mL of water separately and titrate with sodium thiosulfate standard titration solution. During titration, stir with a magnetic stirrer to keep the solution thoroughly mixed. After titrating until the brown color of iodine fades, add 2mL of starch indicator solution separately and continue titrating until the blue color of the solution fades, which is the titration endpoint

A.4.3 Result Calculation

The mass fraction w2 of free glycerol is calculated according to the formula

In the formula:

V0- the volume of the blank titration consumed by the sodium thiosulfate standard titration solution, in milliliters (mL)

V1- The volume of sodium thiosulfate standard titration solution consumed in the titration of the sample aqueous solution, in milliliters (mL)

c - The actual concentration of sodium thiosulfate standard titration solution, in moles per liter (mol/L)

M - Molar mass of glycerol, in grams per mole (g/mol) [M (C3H8O3)=92]

m - mass of the sample, in grams (g)

50/100- Volume ratio of sample solution

1000- Volume conversion factor

4- Conversion factor

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