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Edible gelatin is widely used as a thickening agent in the food processing industry. If it is frozen, food coloring, fudge, ice cream, cool, yoghurt, frozen food, etc., therefore, the safety of gelatin and people's health is extremely high. close relationship. Bleaching agents such as sulfites and their salts are often added during the production of gelatin. The most important harmful substance in this bleaching agent is sulfur dioxide. The content of sulfur dioxide in gelatin can be effectively measured using an automated Kjeldahl apparatus.
At present, there are two methods for the determination of sulfur dioxide and sulfite in foods under the national standard law: pararosaniline hydrochloride and distillation, and the national standard method for sulfur dioxide in gelatin is all glass distillation. This method requires customizing full glass The instrument, which takes a long time to evaporate, cannot be adapted to the batch sample test in the inspection industry. There are also reports in the literature that the use of direct distillation method to determine the content of sulfur dioxide in gelatin, although the need for complete distillation instrument in the national standard is eliminated, but the distillation efficiency is not significantly improved, and the direct heating method of the heating source temperature is not good control, the absorption of lead acetate polluted environment. In this paper, the Kjeldahl nitrogen analyzer is similar to the distillation method in that the Kjeldahl nitrogen analyzer is used for the determination of sulfur dioxide in gelatin without any configuration change of the instrument, and the distillation time is greatly shortened (<10 min). Good experimental results, method accuracy and accuracy meet the requirements.
Take about 5.0g of gelatin powder in a 100mL beaker, add 50mL of distilled water, make it completely swell, then transfer to automatic Kjeldahl nitrogen distillation tube, and then rinse the beaker with 50mL distilled water a small number of times, the lotion also transferred to distillation In the tube. Install the distillation tube on the Kjeldahl analyzer and turn it completely to seal it. Place 20 mL of hydrogen peroxide absorbing solution (1+9) in the receiving flask and neutralize it to the end point (add 2 drops of methyl red-methylene blue mixed indicator to the hydrogen peroxide solution, the solution is light purple, use the hydroxide When the sodium solution is neutralized to the end point, the color is grass green). The receiving tube was placed in a receiving flask and the lower end was immersed in a hydrogen peroxide solution. Press the acid pump, add 20mL of sulfuric acid (1+4), then turn on the distillation switch and heat distillation. When accepting about 120mL bottle, make the receiving tube leave the liquid surface, and then distilled for 1min, close the distillation switch, rinse the outside of the lower end of the receiving tube with a small amount of distilled water, remove the receiving bottle, add 1 drop of the indicator, use sodium hydroxide standard solution Titrate until the color is grass green, and do not fade within 30s is the end point.
The use of automatic Kjeldahl distillation unit for the determination of sulfur dioxide in gelatin has achieved good results, the instrument can be directly used for testing without any modification (preheat 3 to 5 cycles after start-up), for each sample analyzed Only 5~7min, greatly shorten the distillation time, improve the detection efficiency. This method is simple, accurate, high accuracy, and no significant difference with the all-glass distillation instrument, expanding the scope of application of automatic Kjeldahl nitrogen analyzer, can save the cost of testing for enterprises and institutions. 
April 27, 2024