This standard specifies the determination method of cresol red index in soybean products. The cresol red index can determine the degree of heat treatment of soybean products. The cresol red index can be used to assess whether the soybean products are overcooked. This standard is applicable to soybean products and has certain limitations for non-pure soybean products. GB/T 15403-1994 Determination of cresol red index of soybean products GB/T15403-1994 Standard download decompression password: www.bzxz.net

GB/T15403—1994
National Standard of the People's Republic of China
Determination of cresol red index for Soya bean productswwW.bzxz.Net
GB/T15403—1994
This standard is equivalent to the international standard IS05514-1979 "Soybean products - Determination of cresol red index". Subject content and scope of application
This standard specifies the determination method of cresol red index in soybean products. The size of the cresol red index can determine the degree of heat treatment of soybean products. The cresol red index can be used to evaluate whether the product is overcooked.
This standard is applicable to soybean products and has certain limitations for non-pure soybean products. 2 Reference Standards
GB2905 Determination of Crude Protein in Cereal and Legume Seeds3 Terminology
Cresol Red Index: The number of milligrams of cresol red bound to a soybean product containing 500 mg of crude protein under specified operating conditions.
4 Principle
Cresol red can bind to cationic groups in protein molecules, especially soybean protein molecules. When soybean products are heated to cause protein denaturation, the number of cationic groups increases. Therefore, the amount of cresol red that a certain amount of soybean products can bind, that is, the cresol red index, can evaluate the degree of heat treatment of soybean products, especially whether it has been overheated.
Take a certain amount of ground sample and mix it with the cresol red standard solution. After the specified reaction time, the concentration of residual cresol red in the solution is determined by spectrophotometry, and then compared with the initial concentration of the cresol red standard solution, the cresol red index of the sample can be measured. 5 Reagents
The reagents used in this standard are all analytically pure, and water is distilled water or water of equivalent purity. 5.1 Cresol red standard solution, 0.1g/L
Weigh 0.1g cresol red (HG3-3048), (accurate to 1mg) and dissolve it in 40mL 0.1mol/L sodium hydroxide solution, transfer quantitatively to a 1000mL volumetric flask, add water to about 800mL, add 100mL 1mol/L hydrochloric acid, then dilute with water to the scale and mix well. 5.2 Sodium hydroxide (GB629) solution, 0.02mol/L. 5.3 n-hexane.
6 Instruments and equipment
6.1 Pulverizer: no obvious heat during pulverization (such as ball mill); 6.2 Sieve: sieve hole 0.2mm (80 mesh);
6.3 Analytical balance: cold 0.0001g;
6.4 Pipette: 1mL, 20mL;
6.5 Magnetic stirrer: diameter 120mm;
Centrifuge: 3000r/min and equipped with polyethylene centrifuge tube; 6.7 Oscillator;
Approved by the State Bureau of Technical Supervision on December 30, 1994 and implemented on July 1, 1995
GB/T15403-1994
6.8 Spectrophotometer, or colorimeter with interference filter. For samples with a fat content greater than 10%, use; 6.9 micro-mill or mortar;
6.10 a device for removing solvent under reduced pressure (such as a rotary evaporator). 7 Preparation of the sample
Use a pulverizer (6.1) to crush 5-10 g of the sample so that it all passes through the sieve holes of (6.2). If the fat content of the sample exceeds 10%, add an appropriate amount of n-hexane (5.3) to a micro-mill or mortar (6.9) for crushing or grinding, then discard most of the solvent and evaporate under reduced pressure (6.10) at below 60°C to dryness.
8 Analysis steps
8.1 Determination of crude protein content
Determine the crude protein content (nitrogen content × 6.25) according to the method specified in GB2905. 8.2 Determination of cresol red index
Weigh a certain amount of sample in duplicate (accurate to 0.1 mg) so that the protein content reaches 100.0 mg, and place them in 50 mL conical bottles. Use a pipette (6.4) to add 20.0 mL of cresol red standard solution (5.1) respectively, stir on a magnetic stirrer (6.5) for 30 minutes, then transfer the mixture to a centrifuge tube (6.6) and centrifuge until the supernatant is clear, usually at 3000 r/min for about 20 minutes. Or shake on an oscillator (6.7) for 30 minutes, filter, and discard the primary filtrate. Use a pipette (6.4) to draw 1.0 mL of the supernatant (or filtrate) and place it in another small conical flask. Add 20 mL of sodium hydroxide solution (5.2) and mix. After 5 to 10 minutes, use a spectrophotometer or colorimeter (6.8) at a wavelength of 570 nm, use a colorimetric cell with a light path of 1 cm, and use water as a reference to determine the absorbance A1 of the solution. Use the same method to determine the absorbance A2 of the standard cresol red solution (4.1) diluted under the same conditions. 9 Expression of analytical results
Cresol red index is expressed as the number of milligrams of cresol red bound to every 500 mg of crude protein (nitrogen content × 6.25).
Cresol red index = 4-4×10
Where: Ai—absorbance of the remaining cresol red solution after reaction with protein. A—absorbance of the standard cresol red solution after dilution. If the results between the two samples meet the requirement of 10, take the arithmetic mean and report the result, and keep one decimal place for the final result.
10 Repeatability
When the same analyst uses the same instrument and equipment, the relative difference between the results of two samples or consecutive measurements is no more than 5%.
Additional notes:
This standard is proposed by the Ministry of Agriculture of the People's Republic of China. This standard is under the jurisdiction of the National Technical Committee for Agricultural Analysis Standardization. This standard was drafted by the Analysis and Testing Center of the Chinese Academy of Agricultural Sciences. Approved by the State Bureau of Technical Supervision on December 30, 1994 and implemented on July 1, 1995
GB/T15403-1994
The main drafters of this standard are Chang Biying and Liang Dongsheng. Approved by the State Bureau of Technical Supervision on December 30, 1994 and implemented on July 1, 1995
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