Food additive - Oxidized starch detection

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A. 1 Safety Reminder

Some reagents used in the inspection methods of this standard are toxic or corrosive, and caution should be exercised during operation! If splashed onto the skin, rinse immediately with water, and in severe cases, seek immediate treatment

A.2 General Provisions

Unless otherwise specified, only reagents confirmed as analytical pure and Grade III water specified in GB/T6682 shall be used in the analysis.

. The standard titration solution, impurity determination standard solution, formulation, and product used in the test method shall be prepared in accordance with the provisions of GB/T601, GB/T602, and GB/T603 unless otherwise specified; When no solvent is specified, the solution used refers to an aqueous solution

A.3 Identification Test

A.3.1 Microscopic Examination

Oxidized starch that has not undergone gelatinization treatment to maintain its particle structure can be directly observed and identified by microscope to determine the shape, size, and characteristics of starch particles.

. Under the polarized light of the microscope, a typical polarized cross can be observed

A.3.2 Iodine staining

Add 1g of the sample to 20mL of water to form a suspension, and add a few drops of iodine solution. The color range should be dark blue to brownish red.

A.3.3 Copper Reduction; Preparation of alkaline copper tartrate test solution

A.3.3.1.1 Solution A: Take 34.66g of copper sulfate (CuSO4 · 5H2O), which should be free from weathering or moisture absorption, and dissolve with water to a constant volume of 500mL. Store this solution in a small sealed container

Solution B: Take 173g of potassium sodium tartrate (KNaC4H4O6 · 4H2O) and 50g of sodium hydroxide, dissolve with water to a constant volume of 500mL. Store this solution in a small alkali resistant container

Mix solution A and solution B in equal volumes to obtain alkaline copper tartrate test solution

A.3.3.2 Analysis Steps

Weigh 2.5g of the sample and place it in a flask. Add 10mL of 0.82mol/L hydrochloric acid solution and 70mL of water, mix well, reflux in a boiling water bath for 3h, and cool.

. Take 0.5mL of cooling solution and add 5mL of hot alkaline copper tartrate test solution to produce a large amount of red sediment

A.3.4 Identification of oxidized starch (not suitable for low degree oxidized potato starch)

A.3.4.1 Principle

Sodium hypochlorite oxidized starch contains a certain carboxyl group and has anionic properties. Can be dyed with positively charged dyes, such as methylene blue

A.3.4.2 Identification Method

50mg of sample should be suspended in 25mL of 1% methylene blue aqueous solution for 5-10 minutes, and stirred at any time.

. After decanting and removing the supernatant, wash the starch with water. If the sample is sodium hypochlorite oxidized starch, the color will be clearly displayed under a microscope. Through testing, oxidized starch can be distinguished from natural or acid treated starch

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